bluuebunny/crossref_metadata_2025 huggingface dataset:
Epidermal Growth Factor: Receptors in Human Fibroblasts and Modulation of Action by Cholera Toxin
Authors: Hollenberg Morley D. , Cuatrecasas Pedro
Published: May 2006

Epidermal growth factor (EGF) stimulates both DNA and RNA synthesis in contact-inhibited human fibroblasts. Stimulation of DNA synthesis is observed at concentrations as low as 3 pM, is half-maximal at 70 pM, and is maximal at 300 pM EGF. The action of EGF is similar to that of fetal-calf serum, but is distinguished by the time-course of stimulation and by the ability of serum to stimulate further those cells maximally stimulated by EGF. Cells that synthesize DNA in response to physiological concentrations of EGF (10
-11
to 10
-10
M) are insensitive to physiological concentrations of insulin (10
-11
to 10
-10
M) and respond only minimally to very high concentrations of this hormone (10
-6
M). The biological activity of EGF is paralleled by binding of this peptide to fibroblasts in a specific and saturable manner; the dissociation constant is about 800 pM. The binding of EGF is unaffected by either insulin or cholera toxin. Cholera toxin inhibits the action of both EGF and serum. Suppression of DNA synthesis is observed at 0.02 pM toxin, and is maximal at about 2 pM. Cells treated with cholera toxin at these concentrations appear to be otherwise viable by several criteria. The stimulatory effects of EGF are also inhibited by theophylline and dibutyryl cyclic AMP separately or in combination. These observations indicate that fibroblasts possess receptors for EGF by biological and physicochemical criteria, and suggest that a similar if not identical peptide may be amongst those factors in sera which stimulate cell growth. The possibility is considered that EGF and cholera toxin modulate the ability of a cell to initiate polynucleotide synthesis by way of specific cell-surface interactions which in turn alter the levels of intracellular cyclic AMP.
Linear Electric Field-Induced Shifts in Electron Paramagnetic Resonance: A New Method for Study of the Ligands of Cytochrome P-450
Authors: Peisach J. , Mims W. B.
Published: May 2006

The linear electric field shift in paramagnetic resonance has, for the first time, been observed in frozen solutions. The magnitude of the shift parameters, measured at
g
max
of the electron paramagnetic resonance absorption envelope, has been used to characterize lowspin ferric heme mercaptide complexes where the nonmercaptide ligand was varied. The magnitude of the shift provides a measure of the difference between the crystal field contribution of the mercaptide and nonmercaptide ligands. In low-spin ferric cytochrome P-450 of rat liver, the presence of an electric field shift indicates a deviation from inversion symmetry and proves that the axial ligands to the heme are not the same. From the magnitude of the shift and its dependence upon the angle between applied electric and magnetic fields, it is suggested that the non-axial ligand to the heme has a crystal field contribution greater than imidazole and smaller than guanidine.
A New Elastic Potential Function for Rubbery Materials
Authors: Blatz P. J. , Sharda S. C. , Tschoegl N. W.
Published: May 2006

A new four-parameter elastic potential function is proposed which represents data on the elastic deformation of rubbery materials with the same parameters in various deformation fields up to break.
D-Glyceraldehyde-3-Phosphate Dehydrogenase: Three-Dimensional Structure and Evolutionary Significance
Authors: Buehner Manfred , Ford Geoffrey C. , Moras Dino , Olsen Kenneth W. , Rossmann Michael G.
Published: May 2006

A 3.0-Å resolution electron density map of lobster glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12) was computed. The essentially single isomorphous replacement map was very substantially improved by averaging subunits. NAD binds in an open conformation at sites close to subunit interfaces. The coenzyme binding portion of the enzyme has almost the same fold as the corresponding portion of lactate dehydrogenase (EC 1.1.1.27). The presence of this structure in the five enzymes, analyzed so far, that use nucleotide coenzymes might indicate a fundamental primordial structural element.
Charge Transfer Between Amine and Carbonyl
Authors: Kon H. , Szent-Györgyi A.
Published: May 2006

The transfer of a whole electron in the ground state can be demonstrated by the interaction of
p
-phenylenediamine and glyoxal, which leads to the formation of free radicals.
Normal Production of Erythrocytes by Mouse Marrow Continuous for 73 Months
Authors: Harrison David E.
Published: May 2006

Marrow cell transplants from old and young control donors were carried in genetically anemic

W/W
v

recipients whose anemias were cured by successful transplants. After maximum of 36 months and four serial transplants, marrow cell lines from both old and younger control donors continued to produce erythrocytes normally. The oldest marrow cell lines had produced erythrocytes normally for 73 months.

Normal erythrocyte production was demonstrated by: (
1
) cure of the anemia in

W/W
v

recipients, (
2
) normal rather than delayed recovery rate of cured recipients after severe bleeding, and (
3
) normal rather than ineffective response of cured recipients to erythropoietin. Hemoglobin patterns, tested in cured

W/W
v

recipients after the first transplantation, showed that at least 90% of the circulating erythrocytes were of the donor type even in donor lines that had produced erythrocytes continuously for 45 months and were recovering from severe bleeding. Concentrations of cells capable of forming macroscopic spleen colonies were more than two orders of magnitude higher in

W/W
v

mice cured by old or younger marrow than in uncured

W/W
v

mice. Nevertheless, colony-forming unit concentrations declined slowly with successive transplants, and the decline seemed more pronounced at the fourth transplant in old than in younger cell lines.

The hypothesis is suggested that senescence is caused by declines in function of only a few vital cell types. The system for comparing old and younger marrow cell lines offers a model for experiments to test this hypothesis and to identify the cell types whose decline causes aging.
Relatedness Among Contractile and Membrane Proteins: Evidence for Evolution from Common Ancestral Genes
Authors: Weltman Joel K. , Dowben Robert M.
Published: May 2006

A statistical method for quantifying the relatedness among proteins was used to perform 2926 paired comparisons of amino-acid composition among 77 contractile and membrane-associated proteins from diverse species and sources. Relatedness of amino-acid compositions correlates with homology of amino-acid sequence. A high degree of relatedness was detected among K
+
-dependent membrane ATPase of
Streptococcus faecalis
, coupling factors F
1
and CF
1
from mitochondria and chloroplasts, outer fiber protein of cilia, ciliary dynein, tubulin, various actins, and myosin subfragment S-1. Heavy meromyosin and tropomyosin were related to each other but not to the first group of proteins. Differences in the degree of methylation may account for some differences in physiological function. Because of their diverse sources, the high degree of relatedness among these proteins is more compatible with evolution from common ancestral genes than with convergent evolution. Squid axon filarin, molluscan paramyosin, and bacterial flagellins appear to be unrelated either to each other or to any of the other proteins studied. Existence of persistent homologies among so many diverse proteins implies conservation of genetic information during evolution by utilization of codons for preferred amino-acid sequences in various proteins.
A General Theory of Carcinogenesis
Authors: Comings David E.
Published: May 2006

A general hypothesis of carcinogenesis is proposed consisting of the following features: (
1
) It is suggested that all cells possess multiple structural genes (
Tr
) capable of coding for transforming factors which can release the cell from its normal constraints on growth. (
2
) In adult cells they are suppressed by diploid pairs of regulatory genes and some of the transforming genes are tissue specific. (
3
) The
Tr
loci are temporarily activated at some stage of embryogenesis and possibly during some stage of the cell cycle in adult cells. (
4
) Spontaneous tumors, or tumors induced by chemicals or radiation, arise as the result of a double mutation of any set of regulatory genes releasing the suppression of the corresponding
Tr
genes and leading to transformation of the cell. (
5
) Autosomal dominant hereditary tumors, such as retinoblastoma, are the result of germ-line inheritance of one inactive regulatory gene. Subsequent somatic mutation of the other regulatory gene leads to tumor formation. (
6
) The Philadelphia chromosome produces inactivation of one regulatory gene by position effect. A somatic mutation of the other leads to chronic myelogenous leukemia. (
7
) Oncogenic viruses evolved by the extraction of host
Tr
genes with their conversion to viral transforming genes. As a result, in addition to the above mechanisms, tumors may also be produced by the reintroduction of these genes into susceptible host cells.
Attempt to Immunize Guinea Pigs Against Leukemia by Skin Scarification with Leukemic Cell Suspensions
Authors: Gross Ludwik
Published: May 2006

An attempt was made to immunize “strain 2” guinea pigs by superficial skin scarification with small doses of L2C leukemic cell suspensions. Among 203 scarified guinea pigs, 32 developed progressively growing leukemic tumors at the site of skin scarification. In 35 guinea pigs small intradermal tumors that appeared at the site of scarification regressed spontaneously; however, 15 guinea pigs in which the intradermal tumor regressed later developed generalized leukemia. In addition, 13 other animals developed generalized leukemia, without an apparent local tumor formation at the site of scarification. A total of 60 out of 203 scarified guinea pigs (30%) died from leukemia.

143 Guinea pigs that survived the scarification were challenged by subcutaneous inoculation of massive doses (0.5 ml each of a 10-fold dilution from a 10% extract) of leukemic cell extracts and only 48 (34%) developed leukemia; 95 guinea pigs (66%) resisted the challenge and remained in good health. In a control experiment, 156 untreated “strain 2” guinea pigs were inoculated subcutaneously (0.5 ml each) with L2C leukemic cell suspensions of 10
-2
or 10
-3
dilution, and all but two (99%) developed generalized leukemia.
Early Differentiation of Glucagon-Producing Cells in Embryonic Pancreas: A Possible Developmental Role for Glucagon
Authors: Rall Leslie B. , Pictet Raymond L. , Williams Robert H. , Rutter William J.
Published: May 2006

Glucagon and insulin are first detectable at the onset of rat pancreas organogenesis. Initially, the specific activity of glucagon is approximately 100-fold higher than that of insulin. At this early stage, endocrine storage granules, similar to α granules, are identifiable in electron micrographs. The granule characteristics, as well as the relative hormone levels, suggest that the early population of differentiated endocrine cells is in fact composed of glucagon-producing (A) cells. This high level of glucagon is present in the embryo much earlier than the metabolic processes thought to be controlled by this hormone. Moreover, glucagon-producing cells may be the first endocrine cells to differentiate. Other known endocrine products accumulate later, during the terminal stages of organogenesis. These observations suggest that glucagon may have a regulatory function in early embryogenesis.
Phosphorylation of 5-Bromodeoxycytidine in Cells Infected with Herpes Simplex Virus
Authors: Cooper Geoffrey M.
Published: May 2006

5-Bromodeoxycytidine is phosphorylated to 5-bromodeoxycytidine 5′-monophosphate in extracts of cells infected with herpes simplex virus but not in extracts of uninfected cells. The conversion of 5-bromodeoxycytidine to nucleotides and its utilization for DNA synthesis in uninfected cells occurs by deamination of 5-bromodeoxycytidine to 5-bromodeoxyuridine followed by phosphorylation of 5-bromodeoxyuridine to 5-bromodeoxyuridine 5′-monophosphate. In contrast, in cells infected with herpes simplex virus, 5-bromodeoxycytidine is phosphorylated directly to 5-bromodeoxycytidine 5′-monophosphate, which can then be deaminated to 5-bromodeoxyuridine 5′-monophosphate and incorporated into DNA. These results indicate a difference in the substrate specificity of nucleoside kinases induced by herpes simplex virus and the enzymes present in uninfected cells. It is suggested that this difference in substrate specificity between virus-induced and host-cell enzymes may allow selective chemotherapy of herpes simplex infections with 5-bromo- or 5-iododeoxycytidine.
Identification of the Synthesis of Guanosine Tetraphosphate (MS I) as Insertion of a Pyrophosphoryl Group into the 3′-Position in Guanosine 5′-Diphosphate
Authors: Sy Jose , Lipmann Fritz
Published: May 2006

The phosphate transfer system of Haseltine
et al.
, consisting of a ribosomal wash obtained from a stringent strain of
Escherichia coli
, washed ribosomes, GTP, and ATP, was used to prepare large quantities of guanosine tetra- and pentaphosphates, the magic spot compounds MS I and MS II of Cashel and Gallant. In our hands, the Haseltine
et al.
system yielded predominantly guanosine tetraphosphate, ppGpp. This system was used exclusively in the described experiments, with ATP labeled with
32
P in the β- and γ-positions as donor. The β-label was found to produce a
ppG

p

and the γ-label a
ppGp

.
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Furthermore, [
3
H]GDP + [γ-
32
P]ATP yielded ppGpp in a
3
H:
32
P ratio of 1:1. The results indicate a transfer of the terminal pyrophosphoryl group of ATP as a unit.

The position of the transferred pyrophosphoryl was assayed for by preparation of
pG

from
ppG

p

with Zn
++
-activated inorganic pyrophosphatase from yeast. The

pG

was then assayed with 3′-nucleotidase, which liberated practically all the labeled phosphate. This result indicate that the phosphate transfer from ATP to GDP yields guanosine 5′-diphosphate-3′-diphosphate.
Crossreactive Antigens on Human Cells Infected with Rauscher Leukemia Virus and on Human Acute Leukemia Cells
Authors: Mann Dean L. , Halterman Roger , Leventhal Brigid G.
Published: May 2006

A water-soluble component of membranes of cells from a Burkitt's lymphoma cultured cell line was used to develop an antiserum that detects an antigen(s) on acute leukemia cells. This antiserum did not react with nonlymphoid cultured cell lines except for human embryonic kidney cells infected with the Rauscher murine leukemia virus. Absorption studies demonstrated this antigen to be crossreactive with the antigen detected on the human acute leukemia cells.
The Reverse Turn as a Polypeptide Conformation in Globular Proteins
Authors: Crawford James L. , Lipscomb William N. , Schellman Charlotte G.
Published: May 2006

The reverse turn, involving four consecutive amino acids, as a tertiary conformation in globular proteins is defined in terms of dihedral angles, the C
1
α
...C
4
α
distance and the O
1
...H-N
4
hydrogen bond distance. In seven proteins we find 125 examples of turns, comprising 33% of the amino acids in these proteins, as compared with 34% of the residues forming helices and only 17% forming β-sheets. The amino-acid compositions of turns, helices, and β-sheets are analyzed in some detail. We find Asn and Gly mainly in turns, Pro in turns (and at the beginning of helices), and Glu in helices. In these turns a statistical survey indicates that 19% of Asp residues are in the first position, 33% of Pro residues are in the second position, 24% of Asn residues are in the third position, and 26% of Trp residues are in the fourth position.
Microinjection of Rabbit Hemoglobin Messenger RNA into Amphibian Oocytes and Embryos
Authors: Brachet J. , Huez G. , Hubert E.
Published: May 2006

After microinjection of hemoglobin mRNA from rabbit reticulocytes (9S mRNA) into
Xenopus laevis
oocytes, the cytological structure remains normal. The peroxidase reaction does not show an accumulation of synthesized hemoglobin in the germinal vesicle. Fertilized
Pleurodeles Waltlii
eggs synthesize rabbit hemoglobin after injection of 9S mRNA; hemoglobin synthesis decreases as development progresses. Micromeres and macromeres synthesize equal amounts of hemoglobin, despite the fact that the micromeres contain many more ribosomes. Descendants of injected blastomeres divide more slowly and do not differentiate; they ultimately undergo cytolysis.
Nicotinic Acid as a Ligand Affecting Leghemoglobin Structure and Oxygen Reactivity
Authors: Appleby Cyril A. , Wittenberg Beatrice A. , Wittenberg Jonathan B.
Published: May 2006

A small molecule, hitherto called X, which is present in legume root nodules and ligates reversibly to the monomeric protein, leghemoglobin, with formation of a hemochrome structure, is identified as nicotinic acid. The binding constants at pH 5.3 are
K
= 7.3 × 10
5
M
-1
and
K
= 3.0 × 10
4
M
-1
for combination of nicotinic acid with ferric and ferrous leghemoglobin, respectively. This high affinity binding of ligand requires an unsubstituted pyridine ring nitrogen atom and an ionized carboxyl group in the 3-position of the ring. Binding of nicotinic acid is favored at acid pH and is reflected by diminished apparent affinity of leghemoglobin for oxygen.
Isolation of Substances That Stimulate RNA Synthesis from Red Kidney Bean: Their Activities in Lymphocytes and
Escherichia coli
Authors: Harms-Ringdahl M. , Fedorcsák I. , Ehrenberg L.
Published: May 2006

An extract from red kidney beans (
Phaseolus vulgaris
) was fractionated with respect to RNA synthesis-stimulating activity. The activity of the fractions was tested in chicken-spleen lymphocytes cultured in serum-free medium and in plasmolyzed
E. coli
cells.
Lymphocyte
-stimulating activity was found in a fraction called F III. This fraction contained protein and orcinol-positive carbohydrate. The protein (called F III p) responsible for the observed activity was separated from the contaminating carbohydrate by acid precipitation. F III p appears to belong to the group of well-known mitogens of high molecular weight present in red kidney beans. A
bacteria
-stimulating factor was found in a fraction called F V. This factor strongly stimulated RNA synthesis in the bacterial system, and had a weak stimulating effect in the lymphocyte system. In plasmolyzed
E. coli
cells, F V counteracted the inhibiting effect of rifampicin on RNA synthesis.
Unipotent Groups in Invariant Theory
Authors: Hochschild G. , Mostow G. D.
Published: May 2006

The finite generation of the ring of invariants of a special class of unipotent groups is established—namely, unipotent radicals of parabolic subgroups.
Conversion of Neutral to Alkaline Liver Fructose 1,6-Bisphosphatase: Changes in Molecular Properties of the Enzyme
Authors: Pontremoli S. , Melloni E. , De Flora A. , Horecker B. L.
Published: May 2006

Removal of the NH
2
-terminal region of fructose 1,6-bisphosphatase from rabbit liver by digestion with subtillisin, or changes in conformation in this region of the protein produced by exposure to low concentrations of urea, result in similar changes in catalytic and allosteric properties of the enzyme. These changes include shift of the pH optimum to more alkaline pH, and loss of sensitivity to inhibition by AMP. The conformation changes are monitored by changes in the fluorescence of the single tryptophan residue, which is located near the NH
2
-terminus. Thus, the tryptophan-containing peptide appears to determine the functional properties of the native enzyme.
Burkitt's Tumors Contain Particles Encapsulating RNA-Instructed DNA Polymerase and High Molecular Weight Virus-Related RNA
Authors: Kufe D. , Magrath I. T. , Ziegler J. L. , Spiegelman S.
Published: May 2006

Burkitt's lymphomas, linked by previous studies with the DNA-containing Epstein-Barr virus, contain an RNA related in sequence to that of Rauscher leukemia virus. The present study establishes that the viral-related RNA found in Burkitt's tumors is a 70S component encapsulated with RNA-instructed DNA polymerase in a particle possessing a density characteristic of RNA tumor viruses. Further, the DNA synthesized by the Burkitt particles hybridizes specifically to the RNA of Rauscher leukemia virus. Thus, four features characteristic of a known oncogenic RNA agent are also exhibited by particles found with a high (87%) frequency in Burkitt's tumors. The relation between the RNA particle and the Epstein-Barr virus and their etiological roles remains to be elucidated. However, relevant to these issues is the finding reported here that the presence of Epstein-Barr virus information in nonneoplastic cells does not lead to the production of the RNA particles that have been detected now in three different human neoplasias, including leukemias, breast cancer, and Burkitt's disease.
Preservation of Normal Behavior by Enucleated Cells in Culture
Authors: Goldman Robert D. , Pollack Robert , Hopkins Nancy H.
Published: May 2006

BHK-21 fibroblasts and BSC-1 epithelial cells were enucleated with cytochalasin B. The enucleated cells were trypsinized and replated; their subsequent behavior was monitored by light optical techniques. The results demonstrate that the information necessary for attachment, spreading, shape formation, pinocytosis, contact inhibition, and cell locomotion is present in enucleated cytoplasm.
Pineal Protein Kinase: Effect of Enzymic Phosphorylation on Actinomycin D Binding by, and Template Activity of, Chromatin
Authors: Fontana Joseph A. , Lovenberg Walter
Published: May 2006

The ability of protein kinase from bovinepineal gland to phosphorylate calf-thymus chromatin and thereby to alter the association between chromatin DNA and histones was investigated. Phosphorylation of calf-thymus chromatin by pineal protein kinase results in an apparent decreased binding between the histones and DNA in chromatin, as indicated by (
i
) an increase in actinomycin D-binding sites after phosphorylation and (
ii
) an increase in the template capacity of the calf-thymus chromatin after phosphorylation. F
1
histone and F
3
histone are the major histone classes in the chromatin that are phosphorylated by the protein kinase. These results support the hypothesis that pineal protein kinase may function at the transcriptional level.
Higher-Order Curvature and Local Solvability of
D
θ
Authors: Knapp Robert E.
Published: May 2006

Let
E
and
F
be vector bundles and
D
:
E̱
→
F̱
an operator of order
k
. We associate a sequence of invariants H⃝

(
l
)

(
D
),
l
≥ 0 with
D
which generalize the concept of curvature in a natural way. In the case where
D
=
D
θ
is the differential operator of a connection θ on a vector bundle
E
, H⃝
(1)
(
D
θ
) is the classical curvature. Furthermore, we find an interesting geometric interpretation for H⃝
(2)
(
D
θ
). Finally, given regularity assumptions, we find, with the aid of these invariants, necessary and sufficient conditions for local solvability of
D
θ
.
Coupling Between Bacteriochlorophyll and Membrane Protein Synthesis in
Rhodopseudomonas spheroides
Authors: Takemoto J. , Lascelles J.
Published: May 2006

Bacteriochlorophyll-containing membranes from
Rhodopseudomonas spheroides
contain proteins with estimated molecular weights of 26,000, 22,000, 19,000, and 10,000-6,000 (proteins 9, 10, 11, and 15) when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Proteins 9, 10, and 11 may be associated with the reaction center form of bacteriochlorophyll and protein 15, with the light-harvesting form. These proteins were not detected in membranes from nonpigmented wild-type cells grown with high aeration. Proteins 10, 11, and 15 were not found in mutants with blocks in bacteriochlorophyll synthesis, including strain 8-17, which is blocked at the phytolation step. Protein 9 was found in significantly reduced amounts. Apparently, synthesis of the completed bacteriochlorophyll molecule is required for the occurrence of these proteins in the membrane.

Gel autoradiography was used to follow the synthesis of membrane proteins in mutant H-5, which requires δ-aminolevulinic acid for bacteriochlorophyll synthesis. Incorporation of labeled amino acids into proteins 9 and 15 was curtailed preferentially in cells deprived of δ-aminolevulinic acid.
Cytochalasin B: Effect on Lysosomal Enzyme Release from Human Leukocytes
Authors: Zurier Robert B. , Hoffstein Sylvia , Weissmann Gerald
Published: May 2006

The morphological and biochemical consequences of treatment of human peripheral blood leukocytes with cytochalasin B were studied. Incubation of human polymorphs with cytochalasin B resulted in nuclear and cytoplasmic spreading, but not in spontaneous release of lysosomal enzymes. Cytochalasin B inhibited particle uptake. Consequently, phagocytic vacuoles were not observed; instead, granule contents were discharged directly into the surrounding medium when cytochalasin B-treated cells were challenged with zymosan particles. Cytochalasin B enhanced the release of lysosomal enzymes from human polymorphonuclear leukocytes whether these encountered zymosan particles or immune complexes on a nonphagocytosable Millipore filter. Cytochalasin B-treated leukocytes thus constitute a model system for quantitative study of lysosome fusion. Augmented enzyme release was blocked by prior treatment of cells with pharmacological doses of agents that influence the accumulation of cyclic nucleotides (cyclic nucleotides themselves, prostaglandin E
1
) or by compounds that interfere with microtubule function (e.g., colchicine, vinblastine). These observations suggest that one action of cytochalasin B on phagocytic cells is to remove the normal constraints to merger of granules, either with each other or with the plasma membrane, and that intact microtubule function is required for translocation of lysosomes.
Binding of
13
C-Enriched α-Methyl-D-Glucopyranoside to Concanavalin A as Studied by Carbon Magnetic Resonance
Authors: Brewer C. F. , Sternlicht H. , Marcus D. M. , Grollman A. P.
Published: May 2006

Binding of α-methyl-D-glucopyranoside, uniformly enriched with 14%
13
C, to zinc and manganese derivatives of concanavalin A at pH 5.6 was studied by pulsed Fourier transform carbon magnetic resonance techniques. Spin-lattice relaxation (
T
1
) of the [
13
C]carbons of the sugar was measured in the absence and presence of the two transition metal derivatives of the protein. In the presence of the manganese derivative of concanavalin A, selective relaxation of the sugar carbons was observed. The values for
T
1
reflect different distances between the carbons of the bound sugar and the manganese ion. Calculation of the distance between the manganese ion and each carbon of the sugar permit the 3-dimensional orientation of the bound sugar to be determined relative to the transition metal site in the protein. The results indicate that α-methyl-D-glucopyranoside binds to the protein in the Cl chair conformation with its 3- and 4- carbons closest to the manganese ion at a mean distance of 10 Å.
Na
+
-Selective Ionophoric Material Derived from Electric Organ and Kidney Membranes
Authors: Shamoo Adil E. , Albers R. Wayne
Published: May 2006

Material that increases black lipid-membrane (oxidized cholesterol) conductance has been demonstrated in the acid-soluble fraction of tryptic digests of membrane fractions from Electrophorus electric organ and beef kidney. The conductance change elicited by this material is highly selective for Na
+
. The activity of the material was greatly enhanced by passage through DEAE-cellulose. Activity could be destroyed by further incubation with Pronase. Since conductivity increases exponentially with dose of ionophore, the conductive unit may be an oligomer.
A Physiological Mechanism for Hebb's Postulate of Learning
Authors: Stent Gunther S.
Published: May 2006

Hebb's postulate of learning envisages that activation or inactivation of extant synaptic contacts in plastic neural networks depends on the synchronous impulse activity of pre- and postsynaptic nerve cells. The physiological mechanism proposed here for this process posits that at synapses acting according to Hebb's postulate, the receptors for the neurotransmitter are eliminated from the postsynaptic membrane by the transient reversals of the sign of membrane polarization that occur during action potential impulses in the postsynaptic cell. But, since the release of neurotransmitter drives the membrane potential of the synaptic zone towards a level about half-way between the negative-inside resting potential and the positive-inside action potential, it would follow that the membrane patches surrounding the receptors of a synapse whose activity has contributed to setting off the postsynaptic impulse would be spared the full extent of the noxious polarity reversal. This mechanism can account for a neurophysiologically documented example of the operation of Hebb's postulate, namely the plasticity of the connections between fourth- and fifth-order neurons in the visual cortex of cats.
Comparison of Nucleolar Proteins of Normal Rat Liver and Novikoff Hepatoma Ascites Cells by Two-Dimensional Polyacrylamide Gel Electrophoresis
Authors: Orrick Larry R. , Olson Mark O. J. , Busch Harris
Published: May 2006

A two-dimensional polyacrylamide gel electrophoresis technique is presented for separation of acid-extracted proteins of isolated nucleoli of normal rat liver and Novikoff hepatoma ascites cells. About 100 distinct protein spots were resolved. Comparison of the patterns for normal liver and Novikoff hepatoma revealed nine spots with markedly different intensities in the two patterns. Two spots were found that were unique to the normal liver pattern, and one spot was found that was unique to the hepatoma pattern.
Synchronous Mating in Yeast
Authors: Sena Elissa P. , Radin David N. , Fogel Seymour
Published: May 2006

Homogeneous
a
and α unbudded yeast cells in logarithmic phase, grown in supplemented minimal medium and isolated by zonal gradient centrifugation, are used for mating. When these cells are resuspended in aerated defined medium, highly synchronous mating rapidly occurs. Within 20 min of incubation at 30° early sexual pairing is evident; extensive agglutination is observed by 60 min, and cell fusion and bud initiation in zygotes occurs after 60-140 min. Sorbitol gradient fractionation of mating mixtures taken at various times during incubation allows the isolation of zygotes or unmated cells. Zygote preparations 90-95% purified are obtained in quantities suitable for genetic and biochemical analysis. The mating procedure is predictable and reproducible.
The γ-Glutamyl Cycle in the Choroid Plexus: Its Possible Function in Amino Acid Transport
Authors: Tate Suresh S. , Ross Leonard L. , Meister Alton
Published: May 2006

Various anatomic regions of rabbit brain have been examined for activities of the enzymes of the γ-glutamyl cycle. While these enzyme activities were widely distributed in the brain, they are present in much higher concentrations in the choroid plexus than in other parts of the brain. The activities observed are of about the same order of magnitude as found in the kidney. These observations and other considerations suggest that the γ-glutamyl cycle may play a significant role in the transport of amino acids between blood and cerebrospinal fluid.
Isolation, Structure, and Absolute Configuration of a New Natural Insect Juvenile Hormone from
Manduca sexta
Authors: Judy Kenneth J. , Schooley David A. , Dunham Loren L. , Hall M. S. , Bergot B. John , Siddall John B.
Published: May 2006

Two juvenile hormones are isolated from organ cultures of corpora allata of the tobacco hornworm moth,
Manduca sexta
Johannson, and are purified by high-resolution liquid chromatography. These are identified as methyl (2
E
, 6
E
)-(10
R
)-10,11-epoxy-3,7,11-trimethyl-2,6-dodecadienoate, a new natural hormone, and methyl (2
E
,6
E
) - (10
R
,11
S
) - 10,11 - epoxy - 3,7,11 - trimethyl-2,6-tridecadienoate. [
14
C]Methionine is incorporated only into their methoxycarbonyl group. Details of the
in vitro
techniques and the chemical proof of structures are presented. The significance of the occurrence of a new juvenile hormone and the new techniques used for production, isolation, and identification are discussed.
T7 Early RNAs are Generated by Site-Specific Cleavages
Authors: Dunn John J. , Studier F. William
Published: May 2006

Transcription of T7 DNA by purified
Escherichia coli
RNA polymerase without added factors produces long RNA molecules that begin near the left end of T7 DNA and terminate at the end of the early region. An endonuclease has been isolated from uninfected
E. coli
that cleaves these long RNAs at five specific sites to generate RNA molecules essentially the same as the early T7 RNAs observed
in vivo
. This sizing factor, which may be RNase III, can act during or after RNA synthesis. Synthesis of early RNA chains has been shown to start at three strong initiators, spaced about 150-200 base-pairs apart near the left end of T7 DNA. Thus, the five cleavages by sizing factor generate the five early messenger RNAs of T7 plus three overlapping RNAs from the promoter region. RNA chains that are started at two of the strong initiators begin with A; those started at the third begin with G. A few minor initiators have also been observed, from which only short chains seem to be synthesized. Their locations in T7 DNA have not been mapped. Rho factor does not appear to be needed to generate any of these early T7 RNAs.
Conformations of Diphosphopyridine Coenzymes upon Binding to Dehydrogenases
Authors: Lee Chi-Yu , Eichner Ronald D. , Kaplan Nathan O.
Published: May 2006

The binding of oxidized as well as reduced coenzyme to some dehydrogenases has been studied under different concentration ratios and temperatures by nuclear magnetic resonance spectroscopy. A significant difference in the spectral behavior between DPN
+
and DPNH upon binding is interpreted in terms of fast and slow on-off rates relative to the nuclear magnetic resonance time scale in the binding of these two coenzymes. Significant downfield shifts of DPN
+
were observed upon binding, comparable in magnitude to those expected upon opening (destacking) of the coenzymes in the case of chicken-muscle and lobster-tail lactate dehydrogenase (EC 1.1.1.27) and yeast alchol dehydrogenase (EC 1.1.1.1.). A preliminary survey of several other dehydrogenases is consistent with these findings. In the case of 3-phosphoglyceraldehyde dehydrogenase, there is a possibility that the coenzyme exists in the folded form.
F
-Deformations and
F
-Tractions
Authors: Morse Marston
Published: May 2006

Let

M
n

be a compact, connected topological manifold and
F
a continuous mapping of

M
n

into
R
that is “topologically nondegenerate” in the sense of (Morse, M. (1959)
J. d'Analyse Math.
, 7, 189-208). Let
c
be a value of
F
and set

F
c

= {
p
∈

M
n

|
F
(
p
) ≤
c
}. The topological critical points of
F
on

F
c

are finite in number and can be related to the invariants of the homology groups of

F
c

as in the differentiable case.
F
-Deformations and
F
-tractions make this possible.
F
-Tractions are here defined and replace retracting deformations used in the differentiable case. The final relations will serve as a model for similar relations between critical extremals of Weierstrass integrals on Riemannian manifolds.
Evidence of Inter-organ Amino-Acid Transport by Blood Cells in Humans
Authors: Felig Philip , Wahren John , Räf Lars
Published: May 2006

To evaluate the contribution of blood cellular elements to inter-organ transport of amino acids, net exchange across the leg and splanchnic bed of 17 amino acids was determined in seven healthy postabsorptive subjects by use of both whole blood and plasma for analysis. Arterial-portal venous differences were measured in five additional subjects undergoing elective cholecystectomy. By use of whole blood, significant net release of amino acids was noted from the leg and gut, while a consistent uptake was observed by the splanchnic bed. The output of alanine from the leg and gut and the uptake of this amino acid by the splanchnic bed exceeded that of all other amino acids and accounted for 35-40% of total amino-acid exchange. Transport by way of plasma could not account for total tissue release or uptake of alanine, threonine, serine, glutamine, methionine, leucine, isoleucine, tyrosine, and citrulline. For each of these amino acids, significant tissue exchange was calculated to occur by way of the blood cellular elements, the direction of which generally paralleled the net shifts occurring in plasma. For alanine, 30% of its output from the leg and gut and 22% of its uptake by the splanchnic area occurred by way of blood cells. We conclude that the blood cellular elements, presumably erythrocytes, contribute substantially to the net flux of amino acids from muscle and gut to liver in normal postabsorptive humans. Alanine predominates in the inter-organ transfer of amino acids occurring by way of blood cells as well as plasma.
Development of Auditory Neuronal Responses in Avian Embryos
Authors: Konishi Masakazu
Published: May 2006

Neurons in the cochlear nuclei of duck embryos become responsive to tonal stimuli in an orderly spatial and temporal sequence. Cells responding to lower frequencies are recorded before those responding to higher frequencies. Auditory neurons are spatially arranged according to their characteristic frequencies, indicating a point-by-point projection of the basilar membrane. Areas of the nuclei where the apical segment of the basilar membrane projects become responsive to sound before regions representing more basal segments. These progressive changes with age are accompanied by a gradual rise both in neuronal sensitivity and in frequency range of maximum sensitivity. The development of auditory neural responses is timed to prepare the embryo for the onset of prenatal mother-young communication.
Relationship of Replication and Transcription of Simian Virus 40 DNA
Authors: Cowan Kenneth , Tegtmeyer Peter , Anthony D. D.
Published: May 2006

RNA produced by the Simian Virus 40 (SV40) mutant tsA30 during lytic infection of kidney cells of African green monkeys was examined by RNA-DNA competition-hybridization. This mutant is temperature-sensitive in a function (gene
A
) that regulates synthesis of viral DNA. No detectable difference between mutant RNA synthesized at the permissive temperature (33°) and wild-type viral RNA was found. During continuous infection with the mutant at the restrictive temperature (41°) only early viral RNA was produced. When mutant DNA and late RNA synthesis were initiated at the permissive temperature, a shift to the restrictive temperature rapidly terminated synthesis of viral DNA but not that of late viral RNA. The data indicate that the function of gene
A
is required before synthesis of late viral RNA and that after initiation, the production of late RNA continues without further expression of gene
A
or concomittant viral DNA synthesis.
Interferon: Evidence for Its Glycoprotein Nature
Authors: Dorner F. , Scriba M. , Weil R.
Published: May 2006

In an attempt to understand the structure of rabbit interferon, the possibility of carbohydrate being part of the molecule was tested. Interferon incubated with neuraminidase from
Vibrio cholera
is homogeneous in charge as revealed by isoelectric focusing. Treatment of “asialointerferon” with galactose oxidase (EC 1.1.3.9) from
Dactylium dendroides
and subsequent reduction with tritiated sodium borohydride yields labeled material with unimpaired antiviral activity. Enzymic incorporation of
N
-[
14
C]acetylneuraminic acid into tritiated asialointerferon restores the original charge heterogeneity. The newly generated sialointerferon contains both
3
H and
14
C activity. Asialointerferon is retained by an affinity column containing phytohemagglutinin from
Phaseolus vulgaris
and can be displaced from the adsorbent by a glycoprotein of known structure. It is concluded that rabbit interferon is a glycoprotein containing the terminal oligosaccharide sequence sialic acid → galactose.
Cell Envelope and Shape of
Escherichia coli
K12
Authors: Henning Ulf , Rehn Kurt , Hoehn Barbara
Published: May 2006

Rod-shaped “ghosts” that are free of murein have been isolated from
E. coli
. The shape of these “ghosts” is maintained by a unit membrane soluble in sodium dodecyl sulfate. Ghosts consist of about 20-30% phospholipid (almost exclusively phosphatidylethanolamine) and 50-60% protein; a large fraction of the remaining material is lipopolysaccharide. Sodium dodecyl sulfate-gel electrophoresis reveals 4-5 different bands corresponding to molecular weights between 10,000 and 40,000. Treatment of ghosts with Pronase reduces this number to 3, and the rod shape still is not lost. Results of treatment of ghosts with a crude extract from
Dictyostelium discoideum
have supplied tentative evidence that at least one of these proteins is involved in the maintenance of rod shape. It does not appear too unlikely that these polypeptide chains are the final products of the genetic information specifying cellular shape.
Delayed Removal of N-Terminal Methionine from Nascent Globin Chains in Sickle-Cell Anemia Reticulocytes
Authors: Suzuki Haruo , Itano Harvey A.
Published: May 2006

Synthetic αT1 and βT1, the N-terminal tryptic peptides of α-chain and β-chain of hemoglobin, and MetαT1 and MetβT1, peptides in which N-terminal methionyl residues are peptide-bonded to αT1 and βT1, were prepared by the solid-state method of Merrifield. These synthetic peptides were used to establish conditions for chromatographic purification and analysis. When tryptic digests of nascent globin chains from rabbit and sickle-cell anemia reticulocytes incubated with
35
S- and
3
H-labeled amino acids were analyzed, radioactivity not present in tryptic digests of labeled hemoglobin appeared at the elution positions of MetαT1 and MetβT1. The fraction of nascent chains with N-terminal methionine was higher in sickle-cell anemia reticulocytes than in rabbit reticulocytes. If rate of peptide-chain elongation in polysomes is uniform, nascent human chains must attain a greater length before removal of the initial methionyl residue. Length of nascent chain at time of removal was calculated from two independent sets of data, one obtained from [
35
S]methionine incorporation into MetαT1, MetβT1, αT5, and βT5, and the other obtained from [
3
H]lysine and [
3
H]valine incorporation into MetβT1 and βT1.
Lateral Phase Separations in Membrane Lipids and the Mechanism of Sugar Transport in
Escherichia coli
Authors: Linden C. D. , Wright K. L. , McConnell H. M. , Fox C. F.
Published: May 2006

Changes in slope of Arrhenius plots for transport can, in some instances, be detected at two different temperatures for cells that have a relatively simple fatty-acid composition in the membrane lipids. These characteristic temperatures correlate with the characteristic temperatures that define changes of state in membrane phospholipids as revealed by the paramagnetic resonance of the spin label TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl). The higher of these characteristic temperatures is that at which the formation of solid patches of membrane lipids is first detected. The lower is the end point of the course of lateral phase separations, at which all the membrane lipids are in a solid phase. For cells enriched for elaidic acid, the rate of transport increase by as much as 2-fold as the temperature is
decreased
by less than 1°, at the higher characteristic temperature. At this characteristic temperature, lateral phase separations begin in the membrane phospholipids. This is also the temperature where one predicts a striking increase in the lateral compressibility of the membrane lipids. These data are thus interpreted to indicate that a component of the transport system vertically penetrates one or both monolayer faces of the membrane during transport, or that some other event involving the lateral compression of the phospholipids is important for transport.
Temperature-Induced Variations in the Surface Topology of Cultured Lymphocytes Are Revealed by Scanning Electron Microscopy
Authors: Lin P. S. , Wallach D. F. H. , Tsai S.
Published: May 2006

Temperature-induced variations in the surface morphology of cultured lymphocytes were evaluated by scanning electron microscopy. At 25-37° the cells' surfaces are largely obscured by numerous undulating microvilli of various lengths but uniform diameter. Temperature changes alter the number of microvilli, their lengths, diameters, distribution, branching, and fusing. Typically, chilling to 0-4° markedly reduces the number of microvilli and increases the diameter of the survivors in a reversible process. In contrast, heating the cells to about 45° rapidly and irreversibly transforms the ordinarily smooth membrane surface into one with a “cobblestone” morphology. At the same time most microvilli disappear and the few that remain clump into a cap. The data suggest that the low-temperature effects reflect a change in the physical state of membrane lipids, while the high-temperature alterations represent thermotropic protein transitions.
Developmentally Regulated, Carbohydrate-Binding Protein in
Dictyostelium discoideum
Authors: Rosen Steven D. , Kafka John A. , Simpson David L. , Barondes Samuel H.
Published: May 2006

A carbohydrate-binding protein assayed by its ability to agglutinate formalinized sheep erythrocytes is synthesized between 3 and 9 hr after
Dictyostelium discoideum
cells are deprived of food, as the cells become cohesive. Agglutination of erythrocytes by this protein was inhibited by
N
-acetyl-D-galactosamine, D-galactose, and L-fucose, but other monosaccharides had little or no effect. The protein bound completely to Sepharose 4B, and was isolated in highly purified form by elution with D-galactose. It appears to be present on the surface of cohesive but not vegetative slime-mold cells. The possibility that this protein may mediate intercellular adhesion in
Dictyostelium
is considered.
Mechanism of DNA Replication in
Drosophila
Chromosomes: Structure of Replication Forks and Evidence for Bidirectionality
Authors: Kriegstein Henry J. , Hogness David S.
Published: May 2006

The replicating chromosomal DNA in
Drosophila melanogaster
cleavage nuclei has been visualized in the electron microscope as a serial array of closely spaced replicated regions created by pairs of diverging replication forks. The fine structure of the forks is very similar to that observed for the replication forks of bidirectionally replicating bacteriophage DNAs. However, the mean length of the single-stranded gaps in
Drosophila
forks is less than 200 nucleotide residues, much shorter than the gaps in phage forks. This difference in gap length corresponds to the observed difference in the size of Okazaki fragments from
Drosophila
and phage.
The Kinetics of Hemolytic Plaque Formation
Authors: De Lisi Charles P. , Bell George I.
Published: May 2006

A mathematical analysis of the formation of hemolytic plaques in agar is presented. The results can be used to calculate the rate constant for antigen-antibody association and the distribution of antibody secretion rates. The limitations of the treatment and estimates of the expected errors involved are briefly discussed.
Calf Tendon Procollagen Peptidase: Its Purification and Endopeptidase Mode of Action
Authors: Kohn Leonard D. , Isersky Chaviva , Zupnik James , Lenaers Albert , Lee George , Lapière Charles M.
Published: May 2006

The procollagen peptidase activity of calf tendon has been purified. The enzyme has a high degree of specificity for native procollagen and converts both pro α1 and α2, to α1 and α2, respectively. The purified enzyme is an endopeptidase which excises the amino terminal peptide extensions of the precursor chains
in block
; the molecular size and amino-acid composition of the excised peptides compare favorably with those predicted in previous reports. Antisera to the enzyme and to procollagen have been prepared and have been used to characterize the enzyme, the enzymatically excised peptides, and the enzyme-peptide complex in reaction mixtures.