bluuebunny/crossref_metadata_2025 huggingface dataset:
Conformational Interconversions of the Cyclic Hexapeptide Cyclo(Pro-Gly)
3
Authors: Deber Charles M. , Torchia Dennis A. , Wong Simon C. K. , Blout Elkan R.
Published: May 2006

A cyclic hexapeptide, cyclo(Pro-Gly-Pro-Gly-Pro-Gly), has been synthesized; its solution conformations were examined by 220-MHz nuclear magnetic resonance spectroscopy. The solution structures have been deduced, and shown to vary as a function of solvent polarity. In addition, it has been found that this cyclic peptide binds alkali metal cations. While the predominant conformation of this cyclic peptide is 3-fold symmetric in the apolar solvent methylene chloride, an asymmetric structure is preferred in some polar solvents (water, dimethylsulfoxide). However, addition of alkali metal salts, such as sodium thiocyanate, to dimethylsulfoxide solutions of the peptide shifts the conformational equilibrium in favor of a second type of C
3
-symmetric structure, presumably the result of the formation of a stable peptide-metal ion complex. Nuclear magnetic resonance data suggest that the peptide in methylene chloride solution takes up a conformation containing three
cis
′ Pro C
α
-C=O bonds and three
cis
Gly-Pro peptide bonds; that water and dimethylsulfoxide stabilize a conformer in which one (or two) sets of such bonds of a given Pro-Gly unit have undergone interconversion to
trans′/trans
forms; and that alkali metal cations complex the cyclic peptide in a C
3
-symmetric all-
trans′/trans
structure.
Calcium-like Action of Phenethylbiguanide and Related Compounds: Inhibition of Pyruvate Kinase
Authors: Davidoff Frank , Carr Stephen
Published: May 2006

Pyruvate kinase (EC 2.7.1.40) is inhibited by phenethylbiguanide. The kinetics of inhibition are competitive between biguanide and divalent, but not monovalent, metal cation activators of the enzyme; biguanide inhibition thus resembles inhibition by Ca
++
. Alteration of either the polar or nonpolar portion of the phenethylbiguanide molecule quantitatively reduces its effectiveness as an inhibitor of pyruvate kinase, but the kinetics of inhibition remain qualitatively unchanged. Measurements of [
3
H]phenethylbiguanide binding to the enzyme indicate the presence of a single class of about 12 binding sites per enzyme molecule; binding characteristics are not significantly different in the presence of either monovalent or divalent metal cations. Studies with
45
Ca
++
and
54
Mn
++
demonstrate about 4 metal binding sites per enzyme molecule; phenethylbiguanide displaces these metal cations from the enzyme. Studies with several enzymes, dependent upon divalent metal cations, of both metal-bridge and substrate-bridge classes fail to show significant inhibition except at much higher phenethylbiguanide concentrations.
Amino-Terminal Sequences and Sites of
In Vivo
Acetylation of Trout-Testis Histones III and IIb
2
Authors: Candido E. Peter M. , Dixon Gordon H.
Published: May 2006

The sequences of the first 25 residues of histone III, and the first 22 residues of histone IIb
2
, from trout testis have been determined on an automatic protein sequencer. The amino-terminal sequence of trout-testis histone III is identical to the corresponding region of calfthymus histone III, whereas the trout-testis histone IIb
2
sequence differs from that of calf-thymus histone IIb
2
at several positions in the amino-terminal region. Several
in vivo
sites of acetylation of these trout-testis histones have also been determined, by the same automated procedure. In addition to the two main sites at lysyl residues 14 and 23 acetylated in calf-thymus histone III, a lower degree of acetylation at two other sites, lysyl residues 9 and 18, has been detected. Four sites of acetylation have also been detected in trout-testis histone IIb
2
, at lysyl residues 5, 10, 13, and 18. When the amino-acid sequences around the acetylated lysyl residues of different histones are compared, striking similarities are seen. The methods used in these studies should prove useful in elucidation of the locations of chemically stable modifications in other proteins.
Rapid Lateral Diffusion of Phospholipids in Rabbit Sarcoplasmic Reticulum
Authors: Scandella Carl J. , Devaux Philippe , McConnell Harden M.
Published: May 2006

Phospholipid spin labels incorporated in the sarcoplasmic reticulum from rabbit-skeletal muscle undergo rapid lateral diffusion within the plane of the membrane. The diffusion constant,
D
, is 6×10
-8
cm
2
/sec at 37°. With this diffusion constant, a phospholipid molecule can diffuse a distance of the order of 5000 nm in 1 sec.
Microelectrophoretic Application of Cholinergic Compounds, Protein Oxidizing Agents, and Mercurials to the Chemically Excitable Membrane of the Electroplax
Authors: Castillo J. Del , Bartels E. , Sobrino J. A.
Published: May 2006

Cholinergic compounds, protein oxidizing agents, heavy metal ions, and organic mercurials were microelectrophoretically (or electro-osmotically) applied to the innervated surface of the isolated electroplax of
Electrophorus electricus
. Phasic potential changes, resembling those observed under similar conditions in frog muscle, followed not only pulses of the common cholinergic drugs, but were also elicited by
o
-iodosobenzoate,
p
-chloromercuribenzoate, and Hg
++
ions. These results suggest that cholinergic receptors of both the electroplax and amphibian endplates behave in essentially the same manner. The discrepancies previously observed can be attributed mainly to the different techniques of drug application.
Catalytic Accelerations of 10
12
-Fold by an Enzyme-Like Synthetic Polymer
Authors: Kiefer Helen C. , Congdon Wayne I. , Scarpa Ioannis S. , Klotz Irving M.
Published: May 2006

A synthetic polymer, polyethyleneimine containing dodecyl (C
12
H
25
)-chains for binding sites and imidazole moieties for functional catalytic groups, catalyzes the hydrolysis of phenolic sulfate esters by a two-step mechanism resembling that of the corresponding natural enzyme. Quantitative rate studies give kinetic parameters that show that the polymer (
synzyme
) accelerates the rate 10
12
-fold compared to unbound imidazole, and 10
2
-fold compared to a type IIA aryl sulfatase enzyme.
Negative Control of Protein Synthesis after Infection with Bacteriophage T7
Authors: Schweiger Manfred , Herrlich Peter , Scherzinger Eberhard , Rahmsdorf Hans J.
Published: May 2006

T7 phage induces two negative control mechanisms of protein synthesis: (
a
) Host-gene expression is repressed by a “T7 repressor,” and (
b
) early T7 protein synthesis is inhibited by a late phage protein.

(
a
) The repressor for host enzyme synthesis is an early T7 protein. Its gene is none of the known early genes; it is located promotor-proximal to gene 1. The repressor function of this protein can be demonstrated by DNA-dependent enzyme synthesis
in vitro
.

(
b
) Expression of early phage gene is depressed by a late phage protein or by T7 RNA polymerase. Control takes place on the level of transcription.
Chromatin Structure and the Cell Cycle
Authors: Pederson Thoru
Published: May 2006

Pancreatic DNase I is used to probe the structure of chromatin isolated from synchronized HeLa cells. The degree to which DNA in chromatin is protected from DNase attack varies during the G
1
, S, and G
2
phases of the cell cycle. In addition, the DNase sensitivity of chromatin from contact-inhibited African green monkey kidney cells differs from that of actively dividing, subconfluent cultures. These cell cycle-dependent chromatin changes were observed consistently at all enzyme concentrations (5000-fold range) and incubation times (15 min-2 hr) tested. The results indicate that the degree of complexing between DNA and chromosomal proteins changes during interphase, and they suggest that the chromosome coiling cycle of visible mitosis may extend in more subtle form over the entire cell cycle.
Somatic Mutational Transients: Models of Response to Acute and Distributed Doses of Radiation Applied to Growing Plants
Authors: Sand Seaward A.
Published: May 2006

After limited exposures of whole plants to gamma radiation, the induced-mutation frequency, measured in somatic tissue of successively blooming flowers, is a transient function of time. Quantitative interpretation of the data is aided by construction of a cell-generation model. Seven theoretical models are designed to represent interaction between the cell-generation model and seven different modes of application of the radiation treatment. The models provide a structure for integration of the mutational contributions from different floral primordia. These different contributions are distributed over the array of mature flowers by the quantitative relationships of each model. A mathematical expression for the average response of a model can be equated to the average observed response and solved for the implied mutation rate per cell per roentgen.
Activation of C-Type RNA Virus Markers in Mouse Uterine Tissue
Authors: Fowler A. K. , Reed C. D. , Todaro G. J. , Hellman A.
Published: May 2006

Synthetic estrogenic compounds, both steroidal and nonsteroidal, and radiation activate markers of C-type virus information in mouse uterine tissue. Both the group-specific viral antigen and the RNA-directed DNA polymerase can be detected within 4 days after stimulation. These observations strengthen the concept of host-modified control mechanisms for expression of C-type virus markers.
The Mode of Segregation of the Bacterial Cell Membrane
Authors: Green Elizabeth Weaver , Schaechter Moselio
Published: May 2006

The distribution of phospholipids from labeled parental membranes to progeny cells was studied by autoradiography and a minicell system. The minicell experiments showed that, during growth, the parental membrane is diluted at the same rate in cells and in minicells, which indicates that ends of cells are not different from the cylindrical portions with regard to the distribution of parental molecules. The same result was obtained after labeling heme-containing proteins with δ-aminolevulinic acid. The autoradiographic experiments indicate that the membrane segregates in about 250 subunits 4 × 10
4
nm
2
in size. These subunits appear to be conserved during growth.
Synthesis of a Brain-Specific Protein (S100 Protein) in a Homologous Cell-Free System Programmed with Cerebral Polysomal Messenger RNA
Authors: Zomzely-Neurath Claire , York Curtis , Moore Blake W.
Published: May 2006

Polyribosomes, carrying nascent polypeptide chains, were prepared from whole brain, cortex, and hindbrain-medullary white matter of young adult rats. In a homologous cell-free system, a brain-specific protein (S100 protein) was identified in the mixture of polypeptides released from the polyribosomes during incubation for 1 hr at 37°.
De novo
synthesis of the S100 protein was achieved in a reconstituted cerebral cell-free system containing polysome-derived mRNA and 40S + 60S subunits. The radioactively labeled S100 protein synthesized
in vitro
was identified by precipitation with antibody to S100 after addition of purified S100 as a carrier, and migration of the solubilized precipitate on acrylamide gels in the presence of sodium dodecyl sulfate.
In vitro
synthesis of the S100 protein did not occur in analogous cell-free systems derived from hepatic tissue or in a heterologous system containing liver polyribosomes and cerebral enzymes.
Extensive Symmetrical Transcription of Simian Virus 40 DNA in Virus-Yielding Cells
Authors: Aloni Yosef
Published: May 2006

Rapidly labeled RNA was extracted from monkey cells after infection with Simian Virus 40 (SV40) and exposure to short pulses of [
5
-
3
H]uridine late in infection. When this RNA was self-annealed, it became resistant to digestion with ribonuclease. The fraction of RNA that resisted the ribonuclease treatment decreased with increased labeling time, or when a short pulse of radioactivity was followed by incubation with unlabeled uridine and actinomycin D. The RNase-resistant RNA was isolated by chromatography on Sephadex G-100 and shown to be double-stranded by its susceptibility to ribonuclease as a function of salt concentration and temperature. This behavior was not due to RNA-DNA hybrid formation, since deoxyribonuclease had no effect upon the double-stranded molecules, even after their denaturation. The relation of the double-stranded RNA to SV40 was demonstrated by the hybridization of about 50% (corrected value, >90%) of the separated RNA strands with component I of SV40 DNA from plaque-purified virus. After self-annealing in formamide at low temperature, about 10% of the rapidly labeled, viral RNA sedimented at 13 S. This value corresponds in size to about 60% of the SV40 DNA.

These observations indicate that late in infection of monkey cells, SV40 DNA is transcribed symmetrically over a considerable portion of its length, and that subsequently some sequences from one or both of the RNA strands are degraded.
The Spectrum of Cobalt Bovine Procarboxypeptidase A, an Index of Catalytic Function
Authors: Behnke W. David , Vallee Bert L.
Published: May 2006

The spectra of functionally essential, chromophoric metal atoms of metalloenzymes are thought to reflect catalytic potential [Vallee and Williams (1968)
Proc. Nat. Acad. Sci. USA
59, 498]. The spectra of cobalt procarboxypeptidase and their perturbations by substrates and inhibitors are virtually the same as those of cobalt carboxypeptidase; both are consistent with a distorted tetrahedral geometry about the cobalt atom, suggesting irregular coordination geometries and low symmetries of metal-binding sites. We have, therefore, examined the enzymatic properties of cobalt procarboxypeptidase and found that it catalyzes the hydrolysis of a series of haloacylated amino acids at rates equal to or greater than those of native zinc carboxypeptidase. These observations demonstrate the existence both of the catalytic and of the binding sites for haloacylated amino acids of the zymogen, even before activation. Hence, the magnitude of conformational changes at the catalytic site thought to accompany its activation must be very small, no matter what their magnitude might be elsewhere in the molecule. The data support the entatic state hypothesis and suggest that it may profitably guide the exploration of catalytic potential of metalloproteins and metal-protein complexes.
Polypeptide Chain Initiation and Stepwise Elongation with
Artemia
Ribosomes and Factors
Authors: McCroskey Ralph P. , Zasloff Michael , Ochoa Severo
Published: May 2006

The supernatant initiation factor from
Artemia salina
embryos promotes, besides the AUG-dependent binding of fMet-tRNA
f
, the poly(U)-dependent binding of
N
-acetylPhe-tRNA to 40S ribosomal subunits; the bound
N
-acylaminoacyl-tRNA reacts directly with puromycin upon addition of 60S subunits. Both the binding reaction and the synthesis of
N
-acylaminoacyl-puromycin occur in the absence of GTP or other ribonucleoside triphosphates. To a smaller extent, the factor also mediates the 40S ribosomal binding of Met-tRNA
f
and Phe-tRNA; in this case, the bound aminoacyl-tRNA is less reactive with puromycin. After the poly(U)- and supernatant factor-dependent binding of
N
-acetylPhe-tRNA to 40S subunits at low Mg
2+
concentration, binding of a second aminoacyl-tRNA (Phe-tRNA), with ensuing formation of the first peptide bond, is dependent upon the addition of the 60S subunit, elongation factor EF-1, and GTP. Further growth of the polypeptide chain requires translocation and is, therefore, dependent upon the addition of elongation factor EF-2. As with the
Escherichia coli
system, once requirements for translation of the third codon have been met, no further additions are necessary for elongation of a peptide chain.
Differences in the Binding of Fluorescent Concanavalin A to the Surface Membrane of Normal and Transformed Cells
Authors: Shoham Jacob , Sachs Leo
Published: May 2006

The binding of fluorescein-conjugated Concanavalin A to the cell surface has been studied in normal and transformed cells in interphase and mitosis. Binding to the cell surface was in the form of an incomplete ring of fluorescence, and the binding was inhibited by α-methyl-D-mannopyranoside. All the cells were fluorescent when treated with 25-250 μg/ml of fluorescent Concanavalin A. With 10 μg, the cells were all fluorescent after 30 min of binding, but after 0.5-5 min with 10 μg or 30 min with 1 or 2.5 μg, transformed interphase cells showed a higher percentage of cells with surface fluorescence than did normal interphase cells. Trypsinized normal and transformed interphase cells showed the same fluorescence. Binding with 2.5 μg at 4° instead of at 24°, gave a higher percentage of fluorescent cells with trypsinized than with untrypsinized transformed cells. Mitotic normal cells were similar to transformed interphase cells, whereas mitotic transformed cells were intermediate between normal and transformed interphase cells. The results indicate that the use of low concentrations of fluorescent Concanavalin A can show differences in surface fluorescence between normal and transformed, interphase and mitotic, and trypsinized and untrypsinized cells. It is suggested that the observed differences in fluorescence can be explained by differences in affinity of the lectin binding sites and/or differences in the clustering of sites.
Method for Correlation of Proton Magnetic Resonance Assignments in Different Solvents: Conformational Transition of Oxytocin and Lysine Vasopressin from Dimethylsulfoxide to Water
Authors: Glickson J. D. , Urry D. W. , Walter Roderich
Published: May 2006

The peptide amide, primary carboxamide, and aromatic proton resonances were assigned to specific hydrogens of oxytocin and lysine vasopressin (Lys-VP) in water at 23° at pH 2.5 and 4.2, respectively. We started with the spectral assignments of oxytocin and Lys-VP determined in deuterated dimethylsulfoxide (Me
2
SO) and monitored the course of each of these resonances as the proportion of water to Me
2
SO was gradually increased. Changes in each of the two hormones in chemical shifts and in some coupling constants indicate that conformational alterations occur in both oxytocin and Lys-VP during the solvent transition from Me
2
SO to water. This study is a specific application of a general method for correlating spectral assignments in different solvents and for monitoring conformational changes accompanying solvent transitions. Application of this technique requires only that the solvent components be miscible over the entire transitional range, that spectral changes of the solute be simple enough to follow, and that the associated structural changes of the solute be “rapid on the proton magnetic resonance time-scale.”
Selective Increase in Lymphocyte Interferon Response to Vaccinia Antigen after Revaccination
Authors: Epstein Lois B. , Stevens David A. , Merigan Thomas C.
Published: May 2006

Viral antigen prepared by heat inactivation of vaccinia virus stimulated production of interferon in association with transformation of sensitized human lymphocytes
in vitro
. Involvement of a macrophage-lymphocyte interaction in production of interferon stimulated by viral antigen was found in which macrophage greatly augmented the amount of interferon produced by lymphocytes. Reimmunization with live vaccinia virus resulted in a selective increase in the ability of lymphocytes to produce interferon in the presence of viral antigen 4-7 weeks later without a corresponding increase in the degree of already significant lymphocyte transformation. There was no correlation between the extent of lymphocyte transformation and the amount of interferon produced. The augmented interferon response after reimmunization described in this study may be a significant component of the protective effect of immunization with vaccinia against disease occurring after exposure to small-pox.
Self-Association of Gene-32 Protein of Bacteriophage T4
Authors: Carroll Robert B. , Neet Kenneth E. , Goldthwait David A.
Published: May 2006

The self-association of gene-32 protein has been studied by sedimentation equilibrium centrifugation and polyacrylamide gel electrophoresis, in order to better understand its role in DNA replication and genetic recombination. The monomer molecular weight of gene-32 protein is 38,000 in guanidine hydrochloride and 34,000 in sodium dodecyl sulfate, in agreement with the results of Alberts and coworkers. Stable dimers of gene-32 protein occur under various conditions, among which are high ionic strength and pH 10. The occurrence of stable dimers under some conditions and higher aggregates under others indicates there are two types of protein-protein interactions occurring in gene-32 protein self-association. The association that occurs above about 0.1 mg/ml concentration of protein produces at least decamers.

A model for the DNA replication fork is postulated that requires the two different interactions that occur in gene-32 protein aggregation. In the model, gene-32 protein holds the two strands of the DNA duplex in a conformation that prevents their reannealing and, therefore, facilitates replication and recombination.
Changes in Alkaline Ribonuclease Activity During Compensatory Renal Growth
Authors: Rosso Pedro , Diggs James , Winick Myron
Published: May 2006

Unilateral nephrectomy in rats produces an increase in ribonuclease activity in both nuclear and cytoplasmic fractions of the contralateral kidney. The timing of this increase and the changes in the proportion of free activity to protein-bound activity are different in each fraction. A peak in inhibitor-bound ribonuclease, suggesting a higher amount of inhibitor, was found in the cytoplasmic fraction before the increase in RNA/DNA ratio. Ninety-six hours after the operation, ribonuclease was still significantly increased in both the nuclear and cytoplasmic fractions. The inhibitor-bound activity was increased in proportion to cellular RNA, maintaining a ribonuclease activity per μg of RNA similar to the controls.
Self-Complementarity of Terminal Sequences Within Plus or Minus Strands of Adenovirus-Associated Virus DNA
Authors: Koczot Frank J. , Carter Barrie J. , Garon Claude F. , Rose James A.
Published: May 2006

At least 70% of plus or minus strands of adenovirus-associated virus DNA contain self-complementary sequences at or near their termini. Self-annealing of these sequences generates circular molecules that are closed by duplex, hydrogen-bonded segments. The self-annealed segments are sensitive to exonuclease III and have a thermal stability comparable to that of double-stranded DNA molecules. Length measurements of double-stranded adenovirus-associated virus DNA molecules show a bimodal distribution, with the larger component being 10% shorter than SV40 DNA.

The presence of self-complementary terminal sequences in single-stranded molecules of viral DNA has been observed previously only with DNA from adenoviruses. It is thus especially notable that adenovirus-associated virus replication is unconditionally dependent on a helper adenovirus. A possible role for terminal self-complementary sequences in viral DNA replication is suggested.
Experimental Differential Light-Scattering Correction to the Circular Dichroism of Bacteriophage T2
Authors: Dorman Burton P. , Maestre Marcos F.
Published: May 2006

Experimental techniques are presented that can be used to assay and correct for differential light scattering effects in circular dichroism spectra of biological macrostructures. The assay is based upon use of variable detector geometries that collect light over large solid angles. Disrupted T2 virus suspensions and purified T2 phage DNA exhibit geometry-independent spectra; the spectrum of intact T2 virus is highly sensitive to detection geometry. On the basis of spectra obtained after light-scattering correction, the structure of T2 DNA in the phage particle is assigned to the C form. We conclude that: (
i
) The measured circular dichroism of a light-scattering specimen may be highly sensitive to light-detection geometry of the instrument. This effect is indicative of differential scattering intensity for left and right circularly polarized light. (
ii
) Some optically active particles, although they scatter light intensely, exhibit circular dichroism that is independent of detection geometry and, therefore, apparently uninfluenced by differential light scattering. We infer that whether differential light scattering arises may depend upon the presence or absence of ordered asymmetry in the organization of the scattering particle. (
iii
) The circular dichroism of any light-scattering specimen should be measured again in apparatus designed for differential light-scattering correction as a prerequisite to meaningful structural conclusions. (
iv
) Differential scattering effects in circular dichroism may be potentially useful as a probe for large-order organization of the scattering particle.
Structural Characteristics of Some Murine RNA Tumor Viruses Studied by Lactoperoxidase Iodination
Authors: Witte Owen N. , Weissman Irving L. , Kaplan Henry S.
Published: May 2006

Iodination by the noninvasive enzymatic lactoperoxidase technique has been used to study the enzyme-accessible and enzyme-inaccessible proteins of three oncorna viruses (radiation leukemia virus, Moloney leukemia virus, and mouse mammary tumor virus).

The number and relative molecular weight of proteins associated with virion preparations purified on sucrose gradients were characterized by scans of Coomassie blue-stained bands after dodecyl sulfate-polyacrylamide gel electrophoresis. Gel scans from the leukemia viruses are similar, each showing six distinct major protein bands on stained gels. The mammary tumor virus proteins by this analysis are not similar to those of the leukemia viruses.

Enzymatic iodination of intact virion preparations led to the solitary labeling of one of the major proteins of each virus—the 80,000-dalton protein of the leukemia viruses and the 52,500-dalton protein of the mammary tumor virus. These are tentatively positioned as surface (enzyme-accessible) moieties in the virions. Disruption of each virus with a nonionic nonionic detergent before enzymatic iodination led to the labeling of the remaining stainable bands. The four lower molecular weight bands of the leukemia viruses are tentatively positioned as internal (enzyme-inaccessible) components.
Alteration of Ribosomal Protein S4 by Mutation Linked to Kasugamycin-Resistance in
Escherichia coli
Authors: Zimmermann Robert A. , Ikeya Yoshiko , Sparling P. Frederick
Published: May 2006

An alteration in the chromatographic mobility of 30S ribosomal protein S4 from two kasugamycin-resistant (
ksgA
) strains of
E. coli
was observed. The locus determining this alteration frequently cotransduced with
ksgA
but could be separated from it by transduction and conjugation. Since the structural gene for protein S4 is thought to lie some 30 min from
ksgA
on the
E. coli
chromosome, the product of the newly-identified gene may modify protein S4. We propose to designate this gene
ramB
.

Reconstitution of 30S subunits from RNA and protein components of
ksgA ramB
and
ksgA
+
ramB
+
strains demonstrated that ribosomal resistance to kasugamycin was due to altered 16S RNA and not to altered protein S4. The altered 16S RNA was undermethylated, and a methylating enzyme that acts on 16S RNA from
ksgA
strains was present in
ksgA
+
but not in
ksgA
strains.
Surface Circulation of Lakes and Nearly Land-Locked Seas
Authors: Emery K. O. , Csanady G. T.
Published: May 2006

The pattern of surface circulation has been mapped for more than 40 lakes, marginal seas, estuaries, and lagoons. All are within the northern hemisphere, and all except one are known to have a counterclockwise pattern. This consistent pattern is attributed to the drag of wind blowing across the bodies of water. Warmer surface water is displaced to the right-hand shore zone (facing downwind), where it produces greater surface turbulence and, thus, greater wind drag. This effect leads to counterclockwise water circulation regardless of the direction and, within limits, the duration of the wind.
Observations on the pH Dependence of the Glutaminase Activity of a Glutamine Amidotransferase, Carbamylphosphate Synthetase
Authors: Trotta Paul P. , Wellner Vaira P. , Pinkus Lawrence M. , Meister Alton
Published: May 2006

Glutamine-dependent carbamylphosphate synthetase (
Escherichia coli
) is composed of a heavy subunit (molecular weight about 130,000) and a light subunit (molecular weight about 42,000), which can be separated with retention of catalytic activities. The separated heavy subunit can catalyze activation of CO
2
by ATP and synthesis of carbamylphosphate from ammonia (but not from glutamine). The only catalytic activity exhibited by the separated light subunit is the ability to hydrolyze glutamine; the separated heavy subunit does not exhibit glutaminase activity. The pH-activity curve of the glutaminase activity of native carbamylphosphate synthetase exhibits maxima at about pH 4.2 and 9.5, while the glutaminase activity of the separated light subunit exhibits only a single optimum at about pH 6.7. When the light and heavy subunits are recombined, the two pH optima characteristic of native enzyme are restored. Glutaminase activities of native enzyme at both pH optima are similarly inhibited by the glutamine analog, L-2-amino-4-oxo-5-chloropentanoic acid, and also by dithiothreitol. Storage of native enzyme at pH 9 abolishes the glutaminase optimum at acid pH, but greatly increases the activity at alkaline pH. Treatment of native enzyme with
N
-ethylmaleimide increases the glutaminase activity dramatically and converts the pH profile to one that closely resembles that of the isolated light subunit. The data indicate that the same active site is involved in hydrolysis of glutamine at both acid and alkaline values of pH, and that this property of the enzyme depends upon interactions between the heavy and light subunits of native enzyme. The double-optima behavior of native enzyme seems to be related to participation of different catalytic groups of the enzyme which affect the maximum velocity rather than the binding of substrate. The findings offer additional evidence for occurrence of significant interactions between the subunits of carbamylphosphate synthetase, and may have significance in relation to other glutamine amidotransferases, including glutaminases.
Enhancement by Interferon of the Expression of Surface Antigens on Murine Leukemia L 1210 Cells
Authors: Lindahl Pernilla , Leary Patricia , Gresser Ion
Published: May 2006

Preparations of mouse interferon enhanced the expression of surface antigens of murine leukemia L 1210 cells, as determined by their alloantibody-absorbing capacity. The factor responsible for the enhancement of surface antigen expression could not be dissociated from the antiviral activity of interferon by standard physicochemical means. Likewise, interferon did not increase the antibody-absorbing capacity of an interferon-resistant subline of L 1210 cells. We conclude that interferon treatment of L 1210 cells is accompanied by modifications of the cell surface.
Methionine Transfer Ribonucleic Acids of Avian Myeloblastosis Virus
Authors: Elder Kay T. , Smith Alan E.
Published: May 2006

Chick-embryo cells contain four isoaccepting species of methionine transfer RNA (I-IV). One species (I) is the initiator, tRNA

f

Met
, and the others (II, III, and IV) are the donors of internal methionyl residues (tRNA

m

Met
). Over 85% of the tRNA
Met
in purified avian myeloblastosis virus consists of one tRNA

m

Met
species, which resembles host-cell tRNA
Met
IV with respect to chromatographic properties on RPC-5, electrophoretic mobility of the terminal methionyl-oligonucleotide, and activity in cell-free protein synthesis in response to synthetic and natural messenger RNAs. Thus, tRNA
Met
IV of avian myeloblastosis virus is structurally indistinguishable from the corresponding host-cell species, and, although not involved in initiation of viral protein synthesis, is able to function in peptide-chain elongation.
Proton-Coupled Accumulation of Galactoside in
Streptococcus lactis
7962
Authors: Kashket E. R. , Wilson T. H.
Published: May 2006

When cells of the anaerobe
Streptococcus lactis
7962 are deprived of their normal fermentable energy source, active transport of galactosides is completely abolished although the membrane carriers are still capable of facilitating the equilibration of sugars across the cell membrane. In these nonmetabolizing cells it was possible to test the Mitchell hypothesis of obligatory coupling of proton movement with sugar transport. This hypothesis was supported by alkalinization of the medium observed when thiomethylgalactoside was added to a lightly buffered suspension of
S. lactis
cells. Conversely, addition of protons resulted in active transport of thiomethylgalactoside. Accumulation of thiomethylgalactoside to a concentration more than 20-times that in the external medium was induced by suddenly exposing cells to a medium at pH 6; no accumulation of thiomethylgalactoside was observed with cells exposed to pH 8.

Active transport of thiomethylgalactoside occurred in the absence of energy metabolism when
S. lactis
cells were treated with valinomycin. This ionophore allowed intracellular K
+
to flow out, thus imposing a membrane potential (inside negative). This potential resulted in a proton uptake and an associated active transport of galactoside. The membrane potential was measured from the distribution ratio (inside/outside) of K
+
in the presence of valinomycin. The pH gradient was measured from the distribution ratio of [
14
C]methylamine. The protonmotive force, calculated from the membrane potential and the pH gradient, was found to be directly related to the accumulation of galactoside, in accordance with the chemiosmotic hypothesis.
Interaction of Nerve Growth Factor with Surface Membranes: Biological Competence of Insolubilized Nerve Growth Factor
Authors: Frazier William A. , Boyd Linda Forrest , Bradshaw Ralph A.
Published: May 2006

Nerve growth factor was insolubilized by covalent attachment to Sepharose beads. Nerve growth factor-Sepharose was biologically active in both the neurite outgrowth assay for nerve growth factor and in preserving responsive neurons
in vitro
. Modification of the bioassay to detect solubilized activity of nerve growth factor and histological examination of ganglia treated with nerve growth factor-Sepharose revealed that nerve growth factor-Sepharose prepared by reaction in 6 M guanidine hydrochloride released negligible amounts of solubilized nerve growth factor activity. These observations extend the previously noted correlations on the structure and function of nerve growth factor and insulin to include the primary action of these two proteins. Thus nerve growth factor, like insulin, appears to express its biological activity by first binding to a receptor on the surface membrane of responsive cells.
Programming of Cells for Death under Defined Experimental Conditions: Relevance to the Tumor Problem
Authors: Basile Dominick V. , Wood Henry N. , Braun Armin C.
Published: May 2006

An attempt was made in this study to determine more precisely the nature of the factors that are involved in the programming of cells for a form of terminal cellular differentiation that results in death. These studies demonstrated that both the cytokinesins, which are potent inhibitors of plant and animal adenosine 3′:5′-cyclic monophosphate phosphodiesterases, and 8-bromoadenosine 3′:5′-cyclic monophosphate, which is a stable, biologically active form of adenosine 3′:5′-cyclic monophosphate, are highly effective in encouraging differentiation of parenchyma cells into tracheary elements with accompanying death. Since adenosine 3′:5′-cyclic monophosphate and theophylline when used together were also effective, the results reported here suggest that adenosine 3′:5′-cyclic monophosphate is somehow importantly involved in the conversion of parenchyma cells into tracheary elements in this system. The possible significance to the tumor problem generally of the programming of cells for terminal differentiation, with or without resulting death, is discussed.
Adenosine-Mediated Elevation of Cyclic 3′:5′-Adenosine Monophosphate Concentrations in Cultured Mouse Neuroblastoma Cells
Authors: Blume Arthur J. , Dalton C. , Sheppard H.
Published: May 2006

Adenosine causes an increase in the concentration of cyclic AMP in mouse neuroblastoma cells. The amount of increase observed in intracellular cyclic AMP levels due to exogenous adenosine depends greatly on the concentration of a specific cyclic AMP phosphodiesterase inhibitor, 4-(-3-butoxy-4-methoxybenzyl)-2-imidazolidinone. Unstimulated concentrations of cyclic AMP were 29-40 pmol/mg of protein, and concentrations after addition of 0.2 mM adenosine were usually twice as high. The presence of 0.7 mM inhibitor along with 0.2 mM adenosine caused an increase in cyclic AMP levels up to 1000-2000 pmol/mg of protein. In the presence of 0.7 mM inhibitor, 2 μM adenosine gives a half-maximal cyclic AMP elevation. Theophylline blocked the elevation of cyclic AMP concentrations caused by exogenous adenosine. The data show that the cyclic AMP system of mouse neuroblastoma has the necessary receptor components to respond positively to exogenous adenosine. The results presented support a direct effect of adenosine, mediated through its control of intracellular levels, on neuronal elements of the nervous system.
Plasma Membranes from Cultured Muscle Cells: Isolation Procedure and Separation of Putative Plasma-Membrane Marker Enzymes
Authors: Schimmel Steven D. , Kent Claudia , Bischoff Richard , Vagelos P. Roy
Published: May 2006

Partially purified plasma membranes were obtained from chick-embryo muscle cells grown in tissue culture. The purification procedure involved homogenization in buffered isotonic sucrose followed by differential and sucrose density gradient centrifugations. The activities of five plasma-membrane markers, as well as microsomal and mitochondrial markers, were followed throughout the purification. When cultures were labeled with [
125
I]α-bungarotoxin, which binds to the surface of cultured muscle cells, the distributions of bound α-bungarotoxin and Na
+
,K
+
-ATPase (EC 3.6.1.3) activity were nearly identical. The activities of these two plasma-membrane markers were maximal in the upper two fractions of the sucrose density gradient and were purified 5- to 7-fold with respect to total particulate protein. These fractions contained 20-30% of the Na
+
,K
+
-ATPase activity and bound α-bungarotoxin, 4% of the microsomal marker TPNH-dependent cytochrome
c
reductase, 0.2% of the mitochondrial marker succinate-dependent cytochrome
c
reductase, 2.7% of the cellular RNA, and 0.02% of the DNA. The activity of the commonly used plasma-membrane marker, 5′-nucleotidase (EC 3.1.3.5), was low in the upper two sucrose gradient fractions and was maximal in a more dense fraction. The distributions of the other two plasma-membrane markers, leucyl β-naphthylamidase and phosphodiesterase I, were intermediate between Na
+
,K
+
-ATPase and 5′-nucleotidase. The distributions of all markers were similar in preparations from cultures containing mononucleated myogenic cells, multinucleated myotubes, fibroblasts, or all three cell types. Modification of the procedure to include homogenization in the absence of sucrose resulted in a 3.4-fold purification of the membranes containing 5′-nucleotidase, which were shifted to a lower density.
Breakdown of HeLa Cell DNA Mediated by Vaccinia Virus
Authors: Parkhurst J. Rodney , Peterson A. R. , Heidelberger Charles
Published: May 2006

Breakdown of HeLa cell DNA begins within 90 min after infection with vaccinia virus at a multiplicity of infection of 2-plaque-forming units per cell, and ends about 7.5 hr after infection. HeLa cell DNA is degraded to a uniform size of 1 to 2 × 10
7
daltons, as judged by alkaline sucrose sedimentation analysis. The rate of host-cell DNA degradation by vaccinia virus increased directly with the multiplicity of infection. Sedimentation patterns in neutral and alkaline sucrose gradients of viral DNA from infected cells, as well as from partially purified virions, indicated that two size classes of DNA were present. Class 1 DNA sediments like T4 DNA in neutral gradients and has a molecular weight twice that of T4 DNA in alkaline gradients. Class II DNA sediments as a molecule of lower molecular weight than T4 DNA in both types of gradients. Infection of prelabeled HeLa cells with vaccinia virus did not result either in formation of trichloroacetic acid-soluble radioactivity or, upon purification of the virions, radioactivity associated with class I DNA, indicating that vaccinia virus does not reutilize HeLa cell DNA.
Regulation of Glucose Synthesis in Hormone-Sensitive Isolated Rat Hepatocytes
Authors: Zahlten Rainer N. , Stratman Frederick W. , Lardy Henry A.
Published: May 2006

A simplified procedure was developed for isolation of intact, hormone-sensitive liver cells in a high and reproducible yield. These cells produce glucose from various precursors at rates comparable to those achieved in isolated perfused liver. Glucagon enhanced glucose synthesis from pyruvate, dihydroxyacetone, fructose, or xylitol more effectively at low than at high substrate concentration. At high pyruvate concentrations (>2 mM), glucagon or adenosine 3′:5′-cyclic monophosphate (0.1 mM) exerts a curious inhibition of gluconeogenesis that can be reverted to stimulation on addition of ethanol. It is suggested that glucagon and cyclic AMP inhibit pyruvate dehydrogenase and thus limit the supply of reducing equivalents needed for glucose formation. Supporting evidence for hormonal control of pyruvate dehydrogenase in isolated liver cells is provided by the fact that glucagon decreases and insulin increases decarboxylation of [
1
-
14
C]pyruvate. Calcium salts (1.3 mM) enhance glucose formation from pyruvate but greatly enhance the inhibition exerted by the divalent cationophore, A23187. Inhibition by glucagon of glucose synthesis from pyruvate is additive with the effects of A23187 + Ca
++
. However, with dihydroxyacetone as substrate, glucagon partially reverses the inhibition exerted by A23187 + Ca
++
. The results are consistent with glucagon effecting an inhibition of pyruvate dehydrogenase and a stimulation of hexosediphosphatase activities.
Homology Between Type-C Viruses of Various Species as Determined by Molecular Hybridization
Authors: Benveniste Raoul E. , Todaro George J.
Published: May 2006

Two strains of feline leukemia virus, two endogenous feline type-C viruses (RD/CCC group), several endogenous and laboratory strains of murine “leukemia” virus, two rat viruses, two primate viruses (woolly monkey and gibbon ape), as well as hamster, pig, and avian type-C viruses were examined for their relatedness to one another by molecular hybridization. The extent of nucleic-acid homology was determined by hybridization of the various viral RNAs to a [
3
H]DNA product synthesized from each virus. Among the murine type-C viruses (Rauscher, Kirsten, AT-124, and endogenous BALB/c virus) a high degree of homology is observed, although the viruses are not identical. The two primate viruses are also closely related to one another. The feline, rat, hamster, and pig endogenous viruses can be readily distinguished from one another and from the murine and primate viruses since their DNA products share very little or no nucleic-acid homology. However, the murine and primate type-C virus groups possess a surprising degree of relatedness. Feline type-C viruses fall into two distinct groups, the feline leukemia virus group and the RD-114/CCC group, with little detectable nucleic-acid homology between them. Infection of feline or rat cells with type-C virus results in production of the endogenous type-C virus of the species along with the infecting virus.
Mutations Affecting
N
-Acetylglucosaminidase in
Dictyostelium discoideum
Authors: Dimond Randall L. , Brenner Michael , Loomis William F.
Published: May 2006

A procedure for screening several thousand clones for alterations in a specific gene product was apapplied to mutagenized cultures of
Dictyostelium discoideum
. Six strains were recovered which had less
N
-acetylglucosaminidase (EC 3.2.1.30) than the wild type. In addition, we isolated four strains in which the enzyme was temperature-sensitive. The enzyme from one of these strains had an altered substrate affinity.

N
-Acetylglucosaminidase is present at a low level in cells grown on bacteria and increases up to 10-fold during the aggregation stage of development. The enzyme appears to be essential to maintain migrating pseudoplasmodia of normal size, as shown by the fact that all of the mutant strains which accumulate very little
N
-acetyl-glucosaminidase formed only small migrating pseudoplasmodia containing less than 10% the number of cells found in the wild-type pseudoplasmodia. The small pseudoplasmodia migrated at less than a third the rate of wild-type pseudoplasmodia and ultimately formed diminutive fruiting bodies.
N
-Acetylglucosaminidase thus appears to be a developmental enzyme that functions during the migration stage.
Light-Induced Phase Shifts of Circadian Leaf Movements of
Phaseolus:
Comparison with the Effects of Potassium and of Ethyl Alcohol
Authors: Bünning Erwin , Moser Ilse
Published: May 2006

Leaves of
Phaseolus coccineus
were exposed to high concentrations of KCl (0.1-0.3 M) for periods of 4-5 hr, or to ethyl alcohol (5-30%) for periods of 2 hr. The treatment started at various phases of the free-running circadian rhythm in continuous light. Whereas the K
+
pulses induced only advance phase shifts, i.e., shortening of the periods, the alcohol pulses caused stronger advances and also slight delays, i.e., lengthening of the periods. These delays became stronger with lower concentrations of alcohol (1.7%) applied for a longer time. The lengthening effect by alcohol supplied continuously depends on the intensity of light. The rather high intensity of 3500 lux, resulting in very long free-running periods of about 29 hr, inhibits a further strong lengthening by alcohol. The phases reacting with advances to K
+
and to alcohol are about the same phases that respond to light pulses with advances. The advances are reached at earlier phases of the circadian cycle when the concentration of alcohol or the strength of the light pulse is increased. The phases that respond with advances are those which, according to earlier publications, are within the energy-independent part of the cycle. The phases responding with delays belong to the energy-requiring part of the cycle. Consequently, it is suggested that advances are due to accelerated membrane depolarization and delays are due to stabilizing effects on membranes.
Scanning Transmission Electron microscope Studies of Deep-Frozen Unfixed Muscle Correlated with Spatial Localization of Intracellular Elements by Fluorescent X-Ray Analysis
Authors: Bacaner Marvin , Broadhurst John , Hutchinson Thomas , Lilley John
Published: May 2006

Thin sections of deep-frozen unfixed muscle were studied in a scanning electron microscope modified for transmission imaging and equipped with a “cryostage” for vacuum compatibility of hydrated tissue. With an energy-dispersive x-ray analysis system, intracellular atomic species in the scan beam path were identified by their fluorescent x-rays and spatially localized in correlation with the electron optical image of the microstructure. Marked differences are noted between the ultrastructure of deep-frozen hydrated muscle and that of fixed dehydrated muscle. In frozen muscle, myofibrils appear to be composed of previously undescribed longitudinal structures between 400-1000 Å wide (“macromyofilaments”). The usual myofilaments, mitochondria, and sarcoplasmic reticulum were not seen unless the tissue was “fixed” before examination. Fluorescent x-ray analysis of the spatial location of constituent elements clearly identified all elements heavier than Na. Intracellular Cl was relatively higher than expected.