bluuebunny/crossref_metadata_2025 huggingface dataset:
Nerve Membrane Excitation without Threshold
Authors: Cole Kenneth S. , Guttman Rita , Bezanilla Francisco
Published: May 2006

Evidence is presented to show that for a squid axon membrane the potential response,
V
, is a smoothly continuous function of a stimulating current,
I
. This makes it unlikely that an all-or-none or sharp transition phenomenon is a major factor in the processes by which ions cross the normal squid axon membrane and, probably, other excitable membranes.

Spatially uniform
V
and
I
were first produced in the squid axon with internal and external electrode arrangements and later by isolating a short length of axon between external pools of sucrose. Under these simplified conditions, direct experiments and calculations based on the Hodgkin-Huxley empirical conductances agree in showing that the maximum response,
R
, is a continuous, single-valued function of the effect of the stimulus,
S
. The maximum value of Δ
R
/Δ
S
decreased steadily as the temperatures were increased from 25° to 38°C. Uncontrolled fluctuations prevented direct observations of Δ
R
/Δ
S
below 15°C where calculations showed that it rose rapidly as the temperature decreased. Since the conductances are experimental parameters and since Δ
R
/Δ
S
as calculated from them remained finite and continuous event at 6.3°C, this is experimental evidence against an all-or-none threshold excitation.

However there is an all-or-none threshold for the initiation and propagation of an impulse along an axon where
V
and
I
are functions of both time and distance.
CONGO RED DICHROISM WITH DISPERSED AMYLOID FIBRILS, AN EXTRINSIC COTTON EFFECT
Authors: Benditt E. P. , Eriksen N. , Berglund C.
Published: May 2006

The spectral absorption, optical rotatory dispresion, and circular dichroism associated with interaction of Congo red dye with partly purified suspensions of amyloid fibril fragments were examined. A set of phenomena consistent with a Cotton effect was found. A nearly identical set of phenomena was obtained with poly-L-lysine in its α-helical form. The dichroism seen when Congo red binds to amyloid substance in tissue sections can also be interpreted as a Cotton effect. This suggests that some special conformation, presumably in protein, is present in a major constituent of amyloid. This conformation is not present in gamma globulin, Bence-Jones protein, albumin, fibrinogen, or other proteins tested so far. These and other optical properties of amyloid substance can be used to compare amyloid deposits in different human cases and in different species. Extension of the use of polarization microscopy with other dyes that bind to other substances in tissue sections should permit more exquisite probing of the conformation of important macromolecules
in situ
in cells and tissues than has hitherto been possible.
APPLICATION OF
129
I MOSSBAUER EFFECT TO BIOLOGICAL SYSTEMS: STUDIES WITH HEME MODELS
Authors: Pasternak M. , Debrunner Peter G. , DePasquali G. , Hager Lowell P. , Yeoman L.
Published: May 2006

The Mossbauer effect associated with
129
I,
125
Te, and
57
Fe has been applied to investigate structural properties of the axial ligands in ferric-high spin hematoheme-I, hematoheme-Te, and hematoheme-histidine-iodide. The magnitude and sign of the
129
I quadrupole coupling constant (
e
2
qQ
) and the isomer shift, as deduced from the Mossbauer effect spectra, are consistent with an axial,
s-p
hybridized bond of overwhelming σ-character. Identical coupling constant (
e
2
qQ
(
127
I) = -1826 ± 3 MHz) were measured for both heme-I and hematoheme-histidine-iodide. Implications of this result to the nature of ferric-high spin heme-histidine complexing are discussed. A stable heme
125
Te species formed in the electron-capture decay of heme-
125
I is observed, and structural properties of this singly bonded telluride ligand are discussed.
A Protein Binding Assay for Adenosine 3′:5′-Cyclic Monophosphate
Authors: Gilman Alfred G.
Published: May 2006

A simple and sensitive assay for adenosine 3′:5′-cyclic monophosphate (cAMP) has been developed that is based on competition for protein binding of the nucleotide, presumably to a cAMP-dependent protein kinase. The nucleotide-protein complex is adsorbed on a cellulose ester filter. Assay conditions are such that a binding constant approaching 10
-9
M is obtained, and the assay is thus sensitive to 0.05-0.10 pmol of cAMP.
Neurohypophyseal Hormone-Sensitive Adenyl Cyclase of Toad Urinary Bladder
Authors: Bär Hans-Peter , Hechter Oscar , Schwartz Irving L. , Walter Roderich
Published: May 2006

An adenyl cyclase preparation derived from epithelial cells of the urinary bladder of the toad,
Bufo marinus
, is described. This cyclase preparation is specifically stimulated by neurohypophyseal hormones and various synthetic analogs which evoke a hydroosmotic response in the intact bladder. The relative stimulatory effects of these compounds have been compared on the cyclase preparation and in the intact bladder. The peptide concentrations required for half-maximal stimulation (affinity) in the cell-free and intact systems were parallel; however the magnitude of stimulation produced by saturating concentrations of peptides did not correlate. Furthermore, it was found that peptide analogs which inhibit the hydroosmotic effect of [8-arginine]-vasopressin on the intact bladder also inhibit the stimulation of the toad bladder cyclase preparation by vasopressin. Prostaglandin E
1
, mercaptans, and disulfides, which inhibit the hormone-induced hydroosmotic response of the intact bladder, did not antagonize the stimulation of the toad bladder cyclase preparation by vasopressin.
Fluorescent Probe Environment and the Structural and Charge Changes in Energy Coupling of Mitochondrial Membranes
Authors: Chance Britton
Published: May 2006

The use of fluorescent probes to give continuous readouts of the structural states of mitochondrial membranes during energy coupling seems a logical extension of their use in the study of protein structural changes. A clear correlation of the probes' fluorescence characteristics with the acquisition of energy coupling can be demonstrated in fragmented and natural membrane using 1-anilinonaphthalene-8-sulfonate (ANS) and ethidium bromide respectively. The present contribution attempts to bring together contemporary viewpoints of this and other laboratories and the recent experimental data and give some detailed information on probe environment and on the structural or charge changes occurring upon energization.

The energy-dependent region of the membrane is located at an aqueous interface between an outer layer of proteins (presumably cytochromes) and the membrane permeability barrier; the aromatic portion of ANS appears to be located in the lipid phase and the sulfonic acid group in the aqueous phase. The aqueous phase is probably a structured water region near paramagnetic membrane components such as cytochrome. Membrane energization arising from altered redox potential changes of cytochromes (
b
T
) is communicated to the water structure through altered structural states of the hemoproteins, causing a decreased volume of the structured water region and increased interaction with the paramagnetic components in the energized state. Attendant alterations of protonic equilibria of membrane components induce both local and transmembrane changes in charge distribution, with consequent movements of ions, including the probe molecules themselves.
Coboglobins: Oxygen-Carrying Cobalt-Reconstituted Hemoglobin and Myoglobin
Authors: Hoffman B. M. , Petering D. H.
Published: May 2006

In this work we show that it is possible to prepare and study a cobalt-substituted hemoglobin—a coboglobin (Cb).—and that this reconstituted metalloprotein exhibits reversible oxygen binding. The effect of the protein environment on Co(II)-protoporphyrin IX is directly observed by esr measurements on deoxy- and oxy-Cb and by oxygen uptake measurements, all of which may be compared with similar measurements on the free metalloporphyrin. Reversing our point of view, we compare oxygen binding to Cb with that of hemoglobin, and thus investigate the relationship of the metal atom and metaloxygen binding to such characteristics of the nature proteins as cooperative oxygen uptake.
Replication and Repair of DNA in Cells of
Escherichia coli
Treated with Toluene
Authors: Moses Robb E. , Richardson Charles C.
Published: May 2006

DNA synthesis has been studied in
Escherichia coli
cells made permeable to nucleotides by treatment with toluene. Replicative synthesis, as distinguished from repair synthesis, occurs at a rate comparable to that observed
in vivo
; it is dependent on the presence of all four deoxyribonucleoside triphosphates, but does not require exogenous DNA; and it is stimulated by ATP. Furthermore, replicative synthesis can be abolished at the restrictive temperature in DNA temperature-sensitive mutants.
N
-ethylmaleimide completely inhibits this type of synthesis, whereas it does not inhibit repair synthesis. Repair synthesis further differs from replicative synthesis in the following points: it does not require ATP; it persists at the restrictive temperature in DNA temperature-sensitive mutants; it can be induced by endogenous or exogenous nuclease activity; and its demonstration requires a Pol
+
strain.
Messenger Characteristics of Nascent Bacteriophage RNA
Authors: Robertson Hugh D. , Lodish Harvey F.
Published: May 2006

The proteins initiated
in vitro
by nascent bacteriophage f2 RNA strands attached to isolated replicating structures have been analyzed. The observations confirm that coat protein is the major product initiated and completed. Nascent strands direct the initiation of viral maturation protein in amounts similar to the maximum levels observed
in vivo
; this synthesis is independent of translation of the coat protein gene. However, only a fraction of these maturation protein molecules initiated
in vitro
is completed. Nascent RNA molecules also direct the initiation of appreciable amounts of viral RNA polymerase protein, very little of which is completed. Certain constraints on the
in vitro
translation of the polymerase gene from single-stranded RNA appear to be relaxed in the nascent strands, as indicated by the reduced effect of a polar amber mutation in the coat cistron upon polymerase protein initiation from nascent RNA.
Role of Heterogeneity of the Solvation Site in Electronic Spectra in Solution
Authors: Galley William C. , Purkey Robert M.
Published: May 2006

The emission spectra of polar aromatic molecules in rigid, polar solution are shown to depend on the exciting wavelength. Occurrence of the phenomenon depends on both the excited-state lifetime of the chromophore and the degree of rigidity of the medium. The results are interpreted in terms of a model which stresses the contribution of micro-environmental heterogeneity to electronic absorption and emission spectra.
Ribosomal Proteins, XII. Number of Proteins in Small and Large Ribosomal Subunits of
Escherichia coli
as Determined by Two-Dimensional Gel Electrophoresis
Authors: Kaltschmidt E. , Wittmann H. G.
Published: May 2006

Two-dimensional gel electrophoresis separates all of the component proteins of the ribosomal subunits of
Escherichia coli
. This method shows 21 proteins in the 30S, and 34 proteins in the 50S, subunit.
Valine-Specific tRNA-like Structure in Turnip Yellow Mosaic Virus RNA
Authors: Yot Pierre , Pinck Monique , Haenni Anne-Lise , Duranton Henri M. , Chapeville François
Published: May 2006

The 3′ terminal nucleotide of turnip yellow mosaic virus (TYMV) RNA (23-25 S) may be esterified with valine in the presence of ATP and an enzyme preparation from
Escherichia coli
. The nucleotide composition near the valine-binding site is different for TYMV RNA and tRNA
Val
from cabbage, as shown by comparison of the valine adducts of nucleotides labeled with radioactive valine in T
1
RNase digests. Consequently, host tRNA
Val
is not involved in the observed charging of TYMV RNA with valine. The TYMV RNA appears to have a tRNA-like structure, at or near its 3′ end, that is recognized by three different enzymes which specifically catalyze reactions involving tRNA.
Superposition of Excitatory and Inhibitory Influences in the Retina of
Limulus:
Effect of Delayed Inhibition
Authors: Ratliff Floyd , Knight B. W. , Milkman Norman
Published: May 2006

In an optic nerve fiber of the compound eye of the horseshoe crab,
Limulus
, the time course of a train of nerve impulses discharged in response to illumination reflects the interplay of excitatory and inhibitory influences. Responses to sinusoidally modulated excitation and inhibition, as a function of frequency, were measured separately and in combination. A simple linear superposition of the separate frequency responses properly accounts for the composite frequency response for both synchronous and asynchronous modulation of the excitatory and inhibitory influences. In general, the effect on the frequency response of increasing the delay of the inhibitory influence is progressively to shift the maximum amplitude to lower frequencies and gradually to produce pronounced maxima and minima in both the amplitude and phase.
A Virus Associated with SR-Spirochetes of
Drosophila nebulosa
Authors: Oishi K. , Poulson D. F.
Published: May 2006

A virus is associated with a strain of transovarially-transmitted SR-spirochetes, NSR, of
Drosophila
. This virus, designated spv-1, is able to infect and to multiply in another strain of SR-spirochetes, WSR, thereby eliminating the SR condition from the host flies. Spv-1 contains DNA, has a buoyant density of 1.480 in CsCl, and is spherical in shape, measuring 50-60 nm in diameter.
RNA-Dependent DNA Polymerase Activity in Five RNA Viruses: Divalent Cation Requirements
Authors: Scolnick E. , Rands E. , Aaronson S. A. , Todaro G. J.
Published: May 2006

The RNA-dependent DNA polymerase(s) in murine leukemia, murine mammary tumor, and avian myeloblastosis viruses require maganese for optimal activity. The transcription of added synthetic polyribonucleotides is greatly enhanced when manganese is used in place of magnesium. A soluble RNA-dependent DNA polymerase activity has been released from murine leukemia particles in the presence of manganese and high detergent concentrations. Two RNA viruses, visna virus of sheep and a primate syncytial virus, not known to have tumor-producing ability, also contain the polymerase.
DNA-Induced Transformation in
Drosophila:
Evidence for Transmission without Integration
Authors: Fox Allen S. , Duggleby William F. , Gelbart William M. , Yoon Sei Byung
Published: May 2006

A key feature of the exosome model of transformation in
Drosophila melanogaster
is that the DNA segments responsible for the phenomenon are not integrated into the linear structure of the chromosomes. This feature is confirmed by the failure to find whole-body transformants in a series of large-scale experiments, and by the absence of evidence for integration under conditions favoring genetic exchange between chromosomes and introduced DNA.
Messenger and Heterogeneous Nuclear RNA in HeLa Cells: Differential Inhibition by Cordycepin
Authors: Penman S. , Rosbash M. , Penman M.
Published: May 2006

Cordycepin (3′-deoxyadenosine) suppresses the labeling of messenger RNA in HeLa cells. The drug has no effect on either the labeling of nuclear heterogeneous RNA or on the transport of messenger RNA into the cytoplasm. The results suggest that messenger RNA and nuclear heterogeneous RNA are synthesized separately, and that the transcription of messenger RNA is inhibited by the drug.
Magnets Interfere with Pigeon Homing
Authors: Keeton William T.
Published: May 2006

Magnets glued to the backs of experienced pigeons often resulted in disorientation when the birds were released from distances of 17-31 miles (27-50 km) under total overcast, whereas no such disorientation occurred during similar releases under clear skies. The magnets did, however, often cause disorientation when first-flight birds were released under sun, and there was some indication of disturbance to experienced pigeons released under sun at longer distances.
Expression of Differentiated Functions in Hepatoma Cell Hybrids, I. Tyrosine Aminotransferase in Hepatoma-Fibroblast Hybrids
Authors: Schneider Jerry A. , Weiss Mary C.
Published: May 2006

The inducible enzyme tyrosine aminotransferase (TAT) has been investigated in hybrids between rat hepatoma cells and mouse fibroblasts. In the latter the TAT baseline activity is low, and in the presence of steroids does not change. By contrast, the hepatoma cells have high TAT activity, and this activity increases by a factor of 4-6 in the presence of steroids. The hybrid cells, like the fibroblasts, have low TAT activity and are not inducible. Heat inactivation curves demonstrate that the hybrid cells contain both parental forms of TAT, and therefore contain the parental genes specifying the enzyme. The presence in the hybrids of detectable rat TAT and the total absence of its inducibility suggest that a second gene is involved in the regulation of TAT inducibility, and that this gene is not expressed in the hybrids.
A Thrombin-Sensitive Protein of Human Platelet Membranes
Authors: Baenziger Nancy Lewis , Brodie G. N. , Majerus Philip W.
Published: May 2006

The action of thrombin on intact human platelets has been studied with the aid of polyacrylamide gel electrophoresis in sodium dodecylsulfate. A single major membrane protein band with a molecular weight of 190,000 disappears after thrombin treatment, while a new membrane protein with a molecular weight of 107,000 appears. This may represent hydrolysis of the thrombin-sensitive protein. When platelets are disrupted or when the thrombin-sensitive protein is solubilized from membranes prior to thrombin treatment, no hydrolysis occurs. The effect of thrombin on the platelet membrane protein is complete within 2 min which suggests that hydrolysis of this membrane protein may trigger the physiological effects of thrombin on platelets.
Synthesis of a Biologically Active N-Terminal Tetratriacontapeptide of Parathyroid Hormone
Authors: Potts J. T. , Tregear G. W. , Keutmann H. T. , Niall H. D. , Sauer R. , Deftos L. J. , Dawson B. F. , Hogan M. L. , Aurbach G. D.
Published: May 2006

Determination of the amino acid sequence of bovine parathyroid hormone has led to the synthesis of a tetratriacontapeptide corresponding to the amino-terminal 1-34 residues of the native molecule. The specific biological effects of this synthetic peptide on bone and kidney are qualitatively identical to those of the native hormone in classical bioassays
in vivo
and in several systems
in vitro
. Potency of the synthetic peptide equals or exceeds that of a biologically active fragment of comparable size isolated from the native hormone; the synthetic and natural peptides show complete immunological cross-reactivity. Thus, essential requirements for the physiological actions of the peptide on both skeletal and renal tissue are contained within the 34 amino-terminal amino acids. The potency of the synthetic peptide, relative to that of the native (84-amino acid) polypeptide, is greater
in vitro
than
in vivo
; this suggests that the carboxyl terminal two-thirds of the native hormone may protect the circulating polypeptide from rapid metabolic degradation.
Aurintricarboxylic Acid: Inhibitor of Initiation of Protein Synthesis
Authors: Stewart Margaret L. , Grollman Arthur P. , Huang Mou-Tuan
Published: May 2006

Aurintricarboxylic acid prevents the attachment of bacteriophage messenger RNA to ribosomes. As a consequence, initiation of protein synthesis in cell-free extracts prepared from
Escherichia coli
or rabbit reticulocytes is inhibited at concentrations of dye that do not prevent chain extension. Its properties can be distinguished from other agents that inhibit protein synthesis, including sodium fluoride, cycloheximide, and pactamycin.
Glial Cell Function: Uptake of Transmitter Substances
Authors: Henn Fritz A. , Hamberger Anders
Published: May 2006

Rabbit-brain fractions enriched in neuronal cell bodies and in glial cells accumulated norepinephrine, serotonin, dopamine, and γ-aminobutyric acid, substances believed to serve as neurotransmitters in the central nervous system. Both neurons and glia were able to concentrate the monoamine transmitters about 4-fold from a medium containing 0.1-1 μM concentrations. However, the glial-cell fraction concentrated aminobutyrate over a 100-fold from the medium, in contrast to the neuronal fraction, which concentrated this amino acid only 4-fold. The uptake of aminobutyrate by glial cells was 30-50% of that of synaptosome preparations. Its uptake in all fractions was temperature sensitive, sensitive to metabolic inhibitors, and exhibited

K
m

values of 0.72 μM for the neuronal fraction, 0.42 μM for the synaptosomal fraction, and 0.27 μM for the glial-cell fraction. These results are interpreted as evidence that the glial cell is involved in limiting the extracellular build-up of substances that might trigger synaptic transmission by removing any transmitters that may diffuse out of the synaptic cleft during the transmission of impulses. The possible function of the enormous ability of glia and synaptosomes to accumulate aminobutyrate is discussed in light of the actions and distribution of this substance in the central nervous system.
Compartmentalization of Spermine and Spermidine in the Herpes Simplex Virion
Authors: Gibson Wade , Roizman Bernard
Published: May 2006

Enveloped particles of herpes simplex virus produced in human cells in culture contained spermidine and spermine, in a molar ratio of 1.6 ± 0.2. The spermine present within the nucleocapsid is sufficient to neutralize at least 40% of the viral DNA. Disruption of the envelope with nonionic detergent and urea resulted in the selective loss of spermidine. Exogenous ornithine can function as a precursor to host and viral polyamines only before infection.
A Possible Role for RNA Polymerase in the Initiation of M13 DNA Synthesis
Authors: Brutlag Douglas , Schekman Randy , Kornberg Arthur
Published: May 2006

The conversion of single-stranded DNA of bacteriophage M13 to the double-stranded replicative form in
Escherichia coli
is blocked by rifampicin, an antibiotic that specifically inhibits the host-cell RNA polymerase. Chloramphenicol, an inhibitor of protein synthesis, does not block this conversion. The next stage in phage DNA replication, multiplication of the doublestranded forms, is also inhibited by rifampicin; chloramphenicol, although inhibitory, has a much smaller effect. An
E. coli
mutant whose RNA polymerase is resistant to rifampicin action does not show inhibition of M13 DNA replication by rifampicin. These findings indicate that a specific rifampicin-RNA polymerase interaction is responsible for blocking new DNA synthesis. It now seems plausible that RNA polymerase has some direct role in the initiation of DNA replication, perhaps by forming a primer RNA that serves for covalent attachment of the deoxyribonucleotide that starts the new DNA chain.
A Complex Between Initiation Factor IF2, Guanosine Triphosphate, and fMet-tRNA
f
: An Intermediate in Initiation Complex Formation
Authors: Lockwood Arthur H. , Chakraborty Prasanta R. , Maitra Umadas
Published: May 2006

Evidence is presented that suggests the formation of a complex between polypeptide chain-initiation factor IF 2, GTP, and fMet-tRNA
f
. This complex transfers both fMet-tRNA
f
and GTP to 30S ribosomal subunits in the presence of ApUpG and initiation factor IF 1. The resultant 30S initiation complex reacts with 50S subunits to form a 70S initiation complex. fMet-tRNA
f
in this 70S complex reacts with puromycin to form fMet-puromycin. These results suggest that [IF 2, GTP, fMet-tRNA
f
] is an intermediate in the initiation of protein synthesis in
Escherichia coli
.
Stimulation of Glucose Transport in Cultures of Density-Inhibited Chick Embryo Cells
Authors: Sefton Bartholomew M. , Rubin Harry
Published: May 2006

The rate of glucose transport in sparse, rapidly growing chick-embryo fibroblasts is much greater than that in density-inhibited cells. The addition of fresh chicken serum or trypsin to the medium of density-inhibited cells causes a large increase in the rate of glucose transport that is detectable 15 min after addition. The increase in glucose transport precedes the increase in DNA synthesis by 5-6 hr. Only small changes in rates of transport are seen with nucleosides or a nonmetabolizable amino acid. The increase in glucose transport requires protein synthesis but not RNA or DNA synthesis.
Regulation of Methionine Biosynthesis in
Escherichia coli:
Mapping of the
metJ
Locus and Properties of a
metJ
+
/
metJ
-
Diploid
Authors: Su Ching-Hsiang , Greene Ronald C.
Published: May 2006

MetJ
-
mutants of
Escherichia coli
have elevated nonrepressible levels of the enzymes of methionine biosynthesis and
S
-adenosylmethionine synthetase (ATP:L-methionine
S
-adenosyltransferase, EC 2.5.1.6). In
E. coli
, as in
Salmonella typhimurium
, the
metJ
locus is close to
metB
(95% cotransduction of
metB
and
metJ
markers), but in
E. coli
the order is reversed, with
metJ
mapping clockwise to
metB
. A stable merodiploid, heterozygous for
metJ
, is subject to repression by methionine. Thus,
metJ
functions via a diffusible product.
MetJ
could either be a regulatory locus or could code for an enzyme required for the synthesis of a methionine metabolite that functions in the control system.
Heme Binding and Transport—A Spectrophotometric Study of Plasma Glycoglobulin Hemochromogens
Authors: Drabkin David L.
Published: May 2006

A hitherto unreported phenomenon is the immediate production of the spectrum of ferrohemochromogens (in the presence of sodium dithionite) upon the addition
in vitro
of hydroxyhemin (pH 7.6-7.8) to the plasmas or sera, as well as to certain Cohn plasma protein fractions, of all mammalian species thus far examined. This distinctive reaction is characteristic of a coordination complex with heme iron, and is ascribed to a remarkable affinity for heme of certain plasma glycoglobulins, which include hemopexin. Spectrophotometry has permitted estimations of the specific heme-binding capacity (as ferrohemochromogen) of the plasmas, the rate of removal from plasma of injected heme, and the production of bile pigments therefrom. The study leads to a new proposal of the cooperative roles of the glycoglobulin hemochromogens and hematin-albumin in heme transport and bile pigment production.
Organelles in Neuroplasmic (“Axonal”) Flow: Neurofilaments
Authors: Weiss Paul A. , Mayr Robert
Published: May 2006

The electronmicroscopically conspicuous “neurofilaments” in axons manifest a marked constancy of mutual distance at all levels of a nerve fiber regardless of the wide variation of cross-sectional area along the course of a single axon or between different axons. The filaments conform to the rheological flow patterns of the axonal flow and must be viewed as discontinuous, metastable, and transitory linear assemblies of subunits present in the axonal matrix. The grid-like distribution of the filaments in the matrix suggests properties akin to those of liquid crystals of heterogeneous composition.
Assignments in the Carbon-13 Nuclear Magnetic Resonance Spectra of Vitamin B
12
, Coenzyme B
12
, and Other Corrinoids: Application of Partially-Relaxed Fourier Transform Spectroscopy
Authors: Doddrell David , Allerhand Adam
Published: May 2006

High-resolution Fourier transform NMR at 15.08 MHz was used to observe the proton-decoupled natural-abundance
13
C spectra of aqueous solutions of cobinamide dicyanide (0.067 M), cyanocobalamin (0.024 M), dicyanocobalamin (0.14 M), and coenzyme B
12
(0.038 M). Assignments were made with the aid of chemical shift comparisons, off-resonance single-frequency proton decoupling, partially-relaxed Fourier transform spectra, and splittings arising from
13
C-
31
P coupling.

As expected, the
13
C spectra of the coronoids were appreciably more informative than the corresponding proton spectra. Nearly all the lines in the
13
C spectra of the corrinoids were well-resolved single-carbon resonances, in spite of the structural complexity.

Partially relaxed
13
C Fourier transform NMR spectra, which yield spin-lattice relaxation times of each resolved resonance, were found to be a very useful addition to the arsenal of NMR techniques.
Species-Specific and Interspecific Antigenic Determinants Associated with the Structural Protein of Feline C-Type Virus
Authors: Oroszlan S. , Huebner R. J. , Gilden R. V.
Published: May 2006

The group-specific protein of feline leukemia viruses has been isolated by isoelectric focusing. This protein has a molecular weight, calculated from sodium dodecyl sulfate-acrylamide gel electrophoresis, of 25,000 and forms a resolved band in such gels when disrupted virions are analyzed. This protein contains both species-specific antigenic determinants, as well as interspecific cross-reactive determinants, as an integral part of its structure.
Crystallization and Preliminary Structural Analysis of Dihydrolipoyl Transsuccinylase, the Core of the 2-Oxoglutarate Dehydrogenase Complex
Authors: Derosier David J. , Oliver Robert M. , Reed Lester J.
Published: May 2006

Dihydrolipoyl transsuccinylase, one of the three enzymes comprising the
Escherichia coli
2-oxoglutarate dehydrogenase (EC 1.2.4.2) complex, has been crystallized. Studies by x-ray diffraction and electron microscopy establish that the transsuccinylase has octahedral (432) symmetry, i.e., it consists of 24 subunits that are structurally identical.
Pressure-Induced Dissociation of Sedimenting Ribosomes: Effect on Sedimentation Patterns
Authors: Infante Anthony A. , Baierlein Ralph
Published: May 2006

Anomalous sedimentation patterns arise when free ribosomes from sea urchin eggs are centrifuged at high speeds. Pressure-induced dissociation of the ribosomes during sedimentation can explain the peculiar behavior; the assumption of such dissociation also yields estimates of the equilibrium constant (as a function of KCl concentration) and the change in molecular volume (500 ± 100 ml/mol) in the reaction: subunits ⇄ ribosome. Such dissociation during centrifugation may explain many experiments in which apparent reduced sedimentation coefficients for ribosomes, and increased coefficients for the subunits, have been ascribed to conformational changes.
A Transition to a Compact Form of DNA in Polymer Solutions
Authors: Lerman L. S.
Published: May 2006

In the presence of over-threshold concentrations of simple neutral polymers and salts, DNA undergoes a cooperative change in its solution structure. Sedimentation studies at low DNA concentrations show that phage DNA molecules collapse into particles approaching the compactness of the contents of phage heads. The interaction between DNA and polymers is thought to be nonspecifically replusive.
A Radioimmunoassay for Human Prolactin
Authors: Hwang P. , Guyda H. , Friesen H.
Published: May 2006

A radioimmunoassay for primate prolactin has been developed, with [
131
I] monkey prolactin, and antibodies to monkey or human prolactin. The assay is specific for prolactin; human growth hormone, and human and monkey placental lactogen show no significant crossreaction. The assay is sensitive enough to measure prolactin concentrations in the sera of most humans studied. The concentration of prolactin in the serum of normal children and adults of either sex was usually below 30 ng/ml, while very high concentrations (up to 500 ng/ml) were observed in newborn infants. The serum prolactin concentration during the menstrual cycle showed no definite increase in the luteal phase. Of 24 patients with galactorrhea, 20 had prolactin concentrations above 30 ng/ml; the highest value observed was 1500 ng/ml. In contrast, 12 of 13 patients with acromegaly had concentrations within the normal range. During pregnancy, the concentration of prolactin in serum rose progressively from an average of 30 ng/ml in the first trimester to 200 ng/ml at term. Postpartum, prolactin concentrations fell to normal levels after 1-2 weeks. Suckling was a potent stimulus to prolactin release, increasing its concentration in serum some 10- to 20-fold.
Natural Hybridization between the Cholla Cactus Species
Opuntia spinosior
and
Opuntia versicolor
Authors: Grant Verne , Grant Karen A.
Published: May 2006

The sexually reproducing cholla cactus species,
Opuntia spinosior
and
O. versicolor
, hybridize naturally in Arizona to produce hybrid swarms and segregating introgressive populations with a high degree of individual variation. The pattern of variation in these hybrid populations can be compared with that in populations derived from crossing of
O. spinosior
and
O. fulgida
, where the hybrids reproduce vegetatively rather than by seeds. The latter hybrid combination, in marked contrast to the former, results in clonal colonies with little or no observable individual variation.
Heterogeneity of Tubulin Subunits
Authors: Feit Howard , Slusarek Lidia , Shelanski Michael L.
Published: May 2006

Tubulin, the subunit protein of microtubules, is a dimer that sediments at 6 S and has a molecular weight of 110,000. Using high resolution polyacrylamide gel electrophoresis, we have demonstrated the presence of two peptide chains, of molecular weight 56,000 and 53,000, in tubulin purified from brain. Two peptide chains of similar molecular weight were identified in each of the A- and B-tubulins isolated from flagella of sea urchin sperm. In all cases, the protein concentrations in the bands were equal. Each of the subunits ran as a single band when eluted from the gel and electrophoresed again in the same type of gel. Chromatography of purified brain tubulin on DEAE-Sephadex columns gave only a single peak containing both subunits in equal amounts.

Cyanogen bromide peptides were prepared from each of the bands after elution from polyacrylamide gel. While certain of the peptides appear to be common to both subunits, substantial differences exist between them. The tubulin dimer is composed of two nonidentical subunits.
Clock Mutants of
Drosophila melanogaster
Authors: Konopka Ronald J. , Benzer Seymour
Published: May 2006

Three mutants have been isolated in which the normal 24-hour rhythm is drastically changed. One mutant is arrhythmic; another has a period of 19 hr; a third has a period of 28 hr. Both the eclosion rhythm of a population and the locomotor activity of individual flies are affected. All these mutations appear to involve the same functional gene on the X chromosome.
Establishment and Maintenance of Repression by Bacteriophage Lambda: The Role of the
c
I,
c
II, and
c
III Proteins
Authors: Echols Harrison , Green Linda
Published: May 2006

To define the events necessary for the establishment and maintenance of repression in a λ-infected cell, we have studied the requirements for efficient synthesis of the
c
I protein (“λ-repressor”). Three classes of λ mutants defective in the establishment of repression are also defective in the appearance of
c
I protein activity at the normal time. Two of these mutational classes (
c
II
-
and
c
III
-
) probably result from inactivation of λ-specified proteins, but the third class (
c
y
-
) may involve a structural defect. We conclude that at least three regulatory elements are likely to be required for the normal turn-on of
c
I protein synthesis in an infected nonlysogenic cell:
c
II and
c
III proteins and an “active” y-region of λ DNA. From these and other results, the complete role of
c
II and
c
III proteins in the establishment of repression may involve a bifunctional regulatory activity: positive regulation of the
c
I gene and negative regulation of late genes. A possible molecular model for
c
II and
c
III action is discussed. Since the
c
II and
c
III genes are repressed by the
c
I protein under conditions of stable lysogeny, a separate mechanism is required for the maintenance of
c
I protein synthesis. After infection of a lysogen by
c
II
-
phage, the rate of increase of
c
I protein activity is substantially greater than after infection of a nonlysogen. From these and other results, the
c
I protein may also have a bifunctional regulatory activity: positive regulation of the
c
I gene and negative regulation of early lytic genes.
Potassium: Effect on DNA Synthesis and Multiplication of Baby-Hamster Kidney Cells
Authors: Orr C. W. , Yoshikawa-Fukada M. , Ebert J. D.
Published: May 2006

The relations between DNA synthesis, cell multiplication, and external potassium concentration have been investigated in cultured baby-hamster kidney cells. When the potassium concentration was raised from 8 mM to 114 mM by equimolar replacement of sodium, DNA synthesis and cell multiplication were almost completely inhibited. This inhibition was reversible even after 72 hr of incubation in medium with a high concentration of potassium. There is a consistent difference between the cultured cells and polyoma virus-transformed cells in response to high-potassium medium, a higher-potassium concentration being required to inhibit multiplication of polyoma virus-transformed cells to the same extent as that of the nontransformed cells.
Prostaglandin E
1
Effects on Adenosine 3′:5′-Cyclic Monophosphate Concentration and Phosphodiesterase Activity in Fibroblasts
Authors: Maganiello Vincent , Vaughan Martha
Published: May 2006

Incubation of L-929 and L-2071 fibroblasts with prostaglandin E
1
(PGE
1
) caused a rapid increase in the cyclic AMP content of these cells. A maximal effect was produced with 0.2 μg PGE
1
per ml. At a concentration of 4 μg/ml, PGE
2
was almost equally effective, but PGF
2α
and PGA
2
were much less so. 2.6 μM epinephrine, 0.4 mM serotonin, and 0.2% ethanol were without effect. In L-929 cells, cyclic AMP concentrations remained elevated for 2-5 hr, and then declined, although even after a 24-hr incubation the medium contained PGE
1
in a concentration sufficient to increase maximally the cyclic AMP content of cells not previously exposed to this compound. A second addition of PGE
1
after 5 or 24 hr did not produce another increase in the concentration of cyclic AMP. After incubation with PGE
1
for 24 hr, cyclic AMP phosphodiesterase activity, assayed with 0.56 μM substrate, was increased 30-100%; the activity rose further between 24 and 48 hr. It is suggested that the increase in phosphodiesterase activity that appears to be a consequence of prolonged elevation of cyclic AMP concentration may account at least in part for the apparent “refractoriness” to PGE
1
that develops after incubation for several hours with this compound.
Electron Paramagnetic Resonance of Single Crystal Oxycobaltmyoglobin and Deoxycobaltmyoglobin
Authors: Chien James C. W. , Dickinson L. Charles
Published: May 2006

Single crystals of oxycobaltmyoglobin and deoxycobaltmyoglobin have been prepared and found to be isomorphous. The paramagnetic resonance spectra of deoxycobaltmyoglobin yield
g
xx
= 2.33
0
,
g
yy
= 2.32
3
,
g
zz
= 2.02
8
with the z-axis parallel to the “heme” normal. The A
Co
and g tensors share the same principal axes with|
A
Co
∥| = 79 G and|
A
Co
[unk]| = 6 G. A value of
A
N
= 17.5 G was also obtained for the ε-N atom of the F8 histidine. There are two paramagnetic species in oxycobaltmyoglobin having apparently identical g-tensors (
g
ξξ = 2.08
3
,
g
ηη = 2.00
6
, and
g
ζζ = 1.98
9
) but different A
Co
-tensors. Furthermore, g values A
Co
do not share the same principal axes. The
A
Co
-values for one of the species are (
A
xx
= 16.7 G,
A
yy
= 5.95 G, A
zz
= 9.3 G), they are all 40% larger for the other species. The two species are oriented 90° to each other in the crystal. The results from electron paramagnetic resonance studies are consistent with a π-bounded structure for
Co
MbO
2
.
Biochemical Method for Inserting New Genetic Information into DNA of Simian Virus 40: Circular SV40 DNA Molecules Containing Lambda Phage Genes and the Galactose Operon of
Escherichia coli
Authors: Jackson David A. , Symons Robert H. , Berg Paul
Published: May 2006

We have developed methods for covalently joining duplex DNA molecules to one another and have used these techniques to construct circular dimers of SV40 DNA and to insert a DNA segment containing lambda phage genes and the galactose operon of
E. coli
into SV40 DNA. The method involves: (
a
) converting circular SV40 DNA to a linear form, (
b
) adding single-stranded homodeoxypolymeric extensions of defined composition and length to the 3′ ends of one of the DNA strands with the enzyme terminal deoxynucleotidyl transferase (
c
) adding complementary homodeoxypolymeric extensions to the other DNA strand, (
d
) annealing the two DNA molecules to form a circular duplex structure, and (
e
) filling the gaps and sealing nicks in this structure with
E. coli
DNA polymerase and DNA ligase to form a covalently closed-circular DNA molecule.
DNA Modification Methylase Activity of
Escherichia coli
Restriction Endonucleases K and P
Authors: Haberman Allan , Heywood Janet , Meselson Matthew
Published: May 2006

The highly purified restriction endonucleases of
E. coli
K and coliphage P1 transfer methyl groups from
S
-adenosylmethionine to adenine residues of unmodified DNA. Incubation of unmodified DNA with endonucleases K or P and
S
-adenosylmethionine renders the DNA resistant to restriction. The enzymes, therefore, have both restriction endonuclease and modification methylase activities.
Cleavage of DNA by R
1
Restriction Endonuclease Generates Cohesive Ends
Authors: Mertz Janet E. , Davis Ronald W.
Published: May 2006

R
1
restriction endonuclease cleaves duplex DNA at a specific sequence, probably 6 nucleotide pairs in length, by making two single-strand staggered cleavages, generating 5′-phosphoryl and 3′-hydroxyl termini. The single-strand ends produced at each break have identical and complementary sequences of 4 or 6 nucleotides in length. Therefore, the cleavage site possesses a 2-fold rotational axis of symmetry perpendicular to the helix axis. The ends of full-length linear SV40 DNA, generated by R
1
endonuclease cleavage, can be joined by
Escherichia coli
ligase to regenerate duplex, fully infectious, covalently-closed circular molecules. It was further found that
all
R
1
endonuclease-generated ends are identical and complementary. Therefore, any two DNA molecules with R
1
sites can be “recombined” at their restriction sites by the sequential action of R
1
endonuclease and DNA ligase to generate hybrid DNA molecules.
Synthesis of Proteochondroitin Sulfate by Normal, Nanomelic, and 5-Bromodeoxyuridine-Treated Chondrocytes in Cell Culture
Authors: Palmoski M. J. , Goetinck P. F.
Published: May 2006

Chondrocytes grown in cell culture from micromelic chick sterna and 5-bromodeoxyuridine-treated normal cells showed reduced incorporation of sulfate into hyaluronidase-sensitive material as compared to normal chondrocytes. Proteochondroitin sulfate synthesized by normal embryonic chick chondrocytes in cell culture was heterogeneous on chromatography. The major chromatographic component was specifically inhibited in normal chondrocytes treated with 5-bromodeoxyuridine, and this component was absent in nanomelic chondrocytes.
Enhancement of Hexose Entry into Chick Fibroblasts by Starvation: Differential Effect on Galactose and Glucose
Authors: Martineau Roland , Kohlbacher Mary , Shaw Stephen N. , Amos Harold
Published: May 2006

Glucose entry, as measured by 5-min uptake into the acid-soluble fraction, is enhanced 15-30 times by long-term (12-24 hr) hexose starvation of chick fibroblasts. The rate of galactose accumulation in the cells increases only 5 times under the same conditions of starvation. Several carbon and energy sources that were tested for their effect on this “derepression” can be classified as: (
i
) those resembling glucose in blocking the “stimulation,” (
ii
) those permitting full “derepression”; and (
iii
) those partially preventing the enhanced entry. Inhibitors of protein synthesis block enhancement under conditions otherwise conducive to it. We conclude that the glucose and galactose carrier systems are not identical, based largely on the asymmetric “repression” observed when glucose and galactose are compared as “repressors.”
A Comparison of Fe
4
S
4
Clusters in High-Potential Iron Protein and in Ferredoxin
Authors: Carter C. W. , Kraut J. , Freer S. T. , Alden R. A. , Sieker L. C. , Adman E. , Jensen L. H.
Published: May 2006

The structures of both oxidized (HP
ox
) and reduced (HP
red
) high-potential iron protein and of oxidized ferredoxin (Fd
ox
) have been partially refined at 2.0-Å resolution by methods similar to those applied to the protein rubredoxin [Watenpaugh, K. D., Sieker, L. C., Herriott, J. R. & Jensen, L. H. (1971)
Cold Spring Harbor Symp. Quant. Biol.
36, 359-367]. Average bond lengths and angles in the HP
red
and Fd
ox
Fe
4
S
4
*
clusters are the same to within the root-mean square (rms) deviation of each mean value. A preliminary comparison of the two HiPIP oxidation states indicates that the HP
ox
cluster is geometrically similar to the HP
red
cluster, but that it is smaller by 0.1-0.2 Å in certain dimensions. The HiPIP and ferredoxin cluster geometry is also nearly identical to that reported recently for a synthetic analog [Herskovitz, T., Averill, B. A., Holm, R. A., Ibers, J. A., Phillips, W. D. & Weither, J. F. (1972)
Proc. Nat. Acad. Sci.
USA 69, 2437-2441]. An apparent paradox presented by the large difference between the HiPIP and ferredoxin electrode potentials can be resolved by the assumption that the Fe
4
S
4
*
cluster has not two but
three
oxidation states. The fully oxidized (HP
ox
) and fully reduced (Fd
red
) clusters are paramagnetic, and the intermediate state is spin-paired [Tsibris, J. C. M. and Woody, R. W. (1970)
Coord. Chem. Rev.
5, 417-458]. This hypothesis is supported by structural and spectroscopic evidence that the “paired-spin” state exists in both HP
red
and Fd
ox
.
Isolation and Characterization of Myosin from Cloned Mouse Fibroblasts
Authors: Adelstein Robert S. , Conti Mary Anne , Johnson George S. , Pastan Ira , Pollard Thomas D.
Published: May 2006

Myosin has been isolated from cloned mouse fibroblasts, line L-929. Fibroblast myosin: (
i
) binds to rabbit muscle actin and is dissociated from it by ATP, (
ii
) has an ATPase activity that is suppressed by Mg
2+
in 0.6 M KCl and is activated by rabbit muscle actin in the presence of Mg
2+
in 14 mM KCl, (
iii
) forms thin bipolar aggregates in 0.1 M KCl when viewed in the electron microscope, (
iv
) possesses a heavy chain with the same mobility as muscle myosin (molecular weight 200,000) in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In these respects, fibroblast myosin appears to be similar to muscle myosin in structure and function.
Isolation of a Mutant of
Salmonella typhimurium
Dependent on D-Arabinose-5-phosphate for Growth and Synthesis of 3-Deoxy-D-mannoctulosonate (Ketodeoxyoctonate)
Authors: Rick P. D. , Osborn M. J.
Published: May 2006

A new type of auxotrophic mutant of
Salmonella typhimurium
has been isolated that is defective in the synthesis of the 3-deoxy-D-mannooctulosonate (ketodeoxyoctonate) region of the lipopolysaccharide and requires D-arabinose-5-phosphate for growth. Genetic and biochemical evidence indicated that the mutant defect was due to an altered ketodeoxyoctonate-8-phosphate synthetase with an apparent

K
m

for D-arabinose-5-phosphate 35-fold higher than that of the parental enzyme. As a result of this enzymatic lesion, the mutant strain was dependent on exogenous D-arabinose-5-phosphate both for growth and for synthesis of a complete lipopolysaccharide.
Ethidium Bromide as a Cooperative Effector of a DNA Structure
Authors: Pohl Fritz M. , Jovin Thomas M. , Baehr W. , Holbrook J. J.
Published: May 2006

A salt-induced cooperative conformational transition of a synthetic DNA, poly(dG-dC), is reversed by addition of ethidium bromide. Binding of the dye at high salt concentrations is highly cooperative. Circular dichroism spectra of the complex and the kinetic data support a model for this cooperative binding that is formally equivalent to the “allosteric” one proposed for oligomeric proteins by Monod
et al.
Thus, double-helical DNA of at least one defined sequence can undergo a cooperative conformational change in solution, with simple salts and drug molecules as antagonistic effectors. Such transitions may be involved in regulatory phenomena operating directly at the level of nucleic acid structure.