bluuebunny/crossref_metadata_2025 huggingface dataset:
The Elastomeric Rack in Biology
Authors: Eyring Henry , Johnson Frank H.
Published: May 2006

A model designated “The elastomeric rack” is discussed with reference to the mechanism of enzyme catalysis and the necessity of large protein molecules in the process. This model, which represents an extension of the earlier “Rack mechanism,” stems from experimental evidence demonstrating large volume changes of activation or of reaction accompanying various biochemical reactions and more complicated physiological processes. For reasons discussed, the volume changes, as revealed through the influence of increased hydrostatic pressure on reaction rates and equilibria, prove that there are large conformational changes in the protein which, because of numerous cross links in a complex network, lead to additive stress on the substrate-enzyme complex, and thereby to increased reactivity. The manner in which the model serves to account for the influence of changes in the environment (temperature, pressure, chemical composition, electrical fields) on the activity of the protein catalyst, and the modifying action of particular inhibitory or activating substances, alone or in combination, is briefly discussed. The bearing of various considerations on protein denaturation, excitation of nerve, contraction of muscle, specific precipitation, and the divers physiological processes in living cells, including mutation, cancer, and the degenerative diseases of aging, is also briefly discussed.
Molecular Probes of Spermatozoan Structures
Authors: Edelman Gerald M. , Millette Clarke F.
Published: May 2006

Several methods have been devised for the isolation and labeling of structural components of spermatozoa. Rodent spermatozoa were cleaved rapidly and specifically at the junction of the heads and tails by treatment with various proteases, and the separate components were isolated by density-gradient centrifugation. Treatment with reducing agents released the mitochondrial membranes from the midpiece, exposing the underlying tail structures.

Mouse spermatozoa were found to contain about 10
7
sites per cell that bind concanavalin A; most of the sites appear to be on the head, for fluorescein-labeled conjugates of concanavalin A were bound mainly to the acrosomal region. Binding of concanavalin A resulted in rapid agglutination of spermatozoa; mixed agglutinates could be formed with somatic cells, as well as with spermatozoa of other species. Fluorescent probes (naphthalenesulfonic acids) bound to the sperm plasma-membrane and caused an immediate loss of motility. In contrast, ethidium bromide bound to the nuclear structures, but did not cause immediate immobilization. These isolation and probing procedures should facilitate detailed chemical analysis of the major components of mammalian spermatozoa.
In Vitro
Reassembly of Shell-Like Particles from Disrupted Polyoma Virus
Authors: Friedmann T.
Published: May 2006

When purified polyoma virus is exposed to 0.01 M dithiothreitol in the presence of 0.2 M Na
2
CO
3
-NaHCO
3
(pH 10.6) at 0-4°C, the capsids are rapidly disrupted to protein subunits of capsomere size, as judged by density gradient centrifugation, sedimentation equilibrium centrifugation, and electron microscopy. Hemagglutination activity and infectivity of disrupted virus are reduced to below detectable amounts. Removal of the disruption reagents by dialysis at 4°C against 0.05 M Tris-0.14 M NaCl-1 mM EDTA and 0.1 mM 2-mercaptoethanol (pH 8.0) results in a time-dependent reappearance of up to 17% of the starting hemagglutination titer, under optimum conditions of ionic strength, pH, temperature, and virus protein concentration. The recovered hemagglutination activity is found in glycerol gradients associated with a 100S DNA-protein complex consisting mostly of linear aggregates of capsomeres. When the linear complex is treated with pancreatic DNase, the complex is converted into spherical particles, of approximately virus size, that sediment at 140 S (with aggregates at 180 S), as well as on the cushion of half-saturated CsCl at the bottom of the gradients. All reassembled particles are not infectious and have markedly reduced DNA to protein ratios.
Geographic Distribution and Light-Dependent Behavior in
Drosophila
Authors: Grossfield Joe
Published: May 2006

Drosophila
species fall into three classes with respect to the effect of light on their reproductive behavior: Class I, species that mate equally well in light or darkness; Class II, those merely inhibited by darkness; Class III, species whose mating is blocked by darkness. Species in the three classes also differ in the extent of their geographic distribution, with Class I including widely distributed and cosmopolitan species and Class III those that are endemic. Class II species have an intermediate distribution pattern. The behavioral differences among species reflects the degree to which courtship information is locked-in on unique visual stimuli, as well as indicating differences in the underlying genetic architecture of flexible versus specialized forms. It may be anticipated that most species of
Drosophila
will be found light dependent. Similar organizational differences in other forms relying on visual courtship stimuli may be reflected in correlation between distribution and behavioral reliance on a single sensory input. Dependence on a single sensory input offers a unique variety of methods for biological control of species that requires a particular sensory system for information transfer.
Flicker Responses in Monkey Lateral Geniculate Nucleus and Human Perception of Flicker
Authors: Spekreijse H. , Norren D. Van , Berg T. J. T. P. Van Den
Published: May 2006

An analysis was made of the impulse discharge patterns—evoked by sinusoidal luminance modulation—of single cells in the lateral geniculate nucleus of the macaque monkey. The goal was to determine whether a correspondence could be observed between flicker detection by human subjects in psychophysical experiments and electrophysiological measurements of discharge patterns of single cells of the lateral geniculate nucleus. We found that the average discharge patterns of single cells exhibited the following behavior when mean retinal illumination was changed: In the low-frequency region (less than about 10 Hz) the response strength (impulses/sec) is independent of the mean luminance, in accordance with Weber's law; in the high-frequency region (above about 10 Hz) the response depends on the absolute modulation amplitude, in accordance with the Ferry-Porter law. Therefore the main features of human critical flicker frequency data are already present in the cellular (lateral geniculate nucleus) response of the macaque monkey. However, the steepness of high frequency fall-off in the response characteristics of these cells is much less than the corresponding fall-off in the human critical-flicker-frequency curves.
Role of 5S RNA in the Functions of 50S Ribosomal Subunits
Authors: Erdmann V. A. , Fahnestock S. , Higo K. , Nomura M.
Published: May 2006

50S ribosomal subunits from
Bacillus stearothermophilus
can be reconstituted from their dissociated components, namely a 5S RNA-free protein fraction, a 5S RNA-free 23S ribosomal RNA fraction, and purified 5S RNA. The biological activity of reconstituted particles in polypeptide synthesis is dependent on the presence of 5S RNA. In the absence of 5S RNA, particles are produced that have greatly reduced activity in (
a
) polypeptide synthesis directed by synthetic, as well as natural, messenger RNA, (
b
) peptidyl transferase assay, (
c
) [
3
H]UAA binding dependent on peptide chain termination factor R1, (
d
) G factor-dependent [
3
H]GTP binding, and (
e
) codon-directed tRNA binding assayed in the presence of 30S subunits. Thus, 5S RNA is an essential 50S ribosomal component.
Procollagen Peptidase: An Enzyme Excising the Coordination Peptides of Procollagen
Authors: Lapière Charles M. , Lenaers Albert , Kohn Leonard D.
Published: May 2006

A heritable connective tissue disorder of cattle, dermatosparaxis, is characterized by an extreme fragility of the skin and the presence of additional peptides at the N-terminal extremities of the collagen α chains, p-α
1
and p-α
2
.

The existence of an enzyme activity is demonstrated in normal connective tissues that is capable of cleaving these additional N-terminal peptides from dermatosparaxic collagen. The activity is demonstratable with dermatosparaxic collagen in solution, as well as with reconstituted dermatosparaxic collagen fibrils polymerized
in vitro
. It has a pH optimum of about 7.0 and is inhibited by EDTA and mercaptoethanol. Differences in

K
m

and

V
max

values exist depending on the substrate utilized, i.e., p-α
1
or p-α
2
; and the presence of additional amounts of one substrate, p-α
1
, alters the concentration requirement for the second substrate, p-α
2
. The product of the excision reaction with p-α
1
as substrate is an equimolar amount of normal α
1
monomer; the product when p-α
2
is substrate is an equimolar amount of normal α
2
monomer.

The enzyme is present in normal calf skin, tendon, aorta, cartilage, and lung; it can be demonstrated in the skin of rats and humans. The enzyme activity is absent in dermatosparaxic connective tissues, thus suggesting that dermatosparaxis is caused by the absence of a normal enzyme function rather than by the production of an abnormal collagen.
Hypothalamic Alpha- and Beta-Adrenergic Systems Regulate Both Thirst and Hunger in the Rat
Authors: Leibowitz Sarah Fryer
Published: May 2006

Adrenergic and adrenolytic drugs were injected directly into the hypothalamus of the rat brain through permanently implanted cannulas and were found to have reliable effects on water consumption in water-satiated and water-deprived subjects. The beta-adrenergic agonist stimulated thirst, and the beta-adrenergic blocker suppressed thirst. Conversely, the alpha-adrenergic agonist suppressed thirst, and the alpha-adrenergic blocker enhanced thirst. These results demonstrate the existence of a hypothalamic beta-adrenergic “thirst” system which opposes a hypothalamic alpha-adrenergic “water-satiety” system. In view of our earlier results demonstrating the existence in the hypothalamus of an alpha-adrenergic “hunger” system which opposes a beta-adrenergic “food-satiety” system, we suggest that a reciprocal inhibitory relationship between these adrenergic hunger- and thirst-regulating systems provides a neurochemical explanation for the ability of organisms to maintain food and water consumption at a constant ratio. In the regulation of both hunger and thirst, the central cholinergic system mimics the hypothalamic beta-adrenergic system and opposes the hypothalamic alpha-adrenergic system.
Amino Acid Sequences of Two Mouse Immunoglobulin Lambda Chains
Authors: Appella Ettore
Published: May 2006

The amino acid sequences of the lambda chains of two mouse immunoglobulins have been determined. No variations were found between these proteins. The results are compatible with earlier fingerprinting analysis of the two chains, where no differences in the tryptic peptides could be demonstrated. The lack of sequence variations could be the result either of a peculiarly restricted expression of the lambda variable-region genome in the BALB/c myelomas or a small number of germ-line genes involved in the biosynthesis of light chains of the lambda type.
Regulatory Properties of an Inorganic Pyrophosphatase from the Photosynthetic Bacterium
Rhodospirillum rubrum
Authors: Klemme Jobst-Heinrich , Gest Howard
Published: May 2006

In
Rhodospirillum rubrum
, inorganic pyrophosphatase activity is observed in both the cytoplasmic and membrane fractions. The soluble enzyme accounts for about 80% of the total activity in crude extracts, and is the subject of this report. Zn
2+
is required for both activity and stability of the enzyme, which has a molecular weight of approximately 90,000 (gel-filtration determinations). The substrate is MgP
2
O
7
2-
, and free pyrophosphate (P
2
O
7
4-
) is a strong inhibitor. Kinetic experiments indicate homotropic interactions between substrate-binding sites; these interactions are influenced by Mg
2+
, which is an activator. At low concentrations of Zn
2+
, the pyrophosphatase is inhibited by NADH, NADPH, and MgATP; 50% inhibition occurs at 0.4-0.7 mM. These effects are reversed by high concentrations of Zn
2+
(10
-4
-10
-3
M). The nucleotides appear to inhibit activity of the “native” enzyme through an effect on Zn
2+
binding. The
R. rubrum
enzyme seems to be the first known example of a bacterial inorganic pyrophosphatase subject to allosteric regulation.
Inducers of Interferon Inhibit the Mitotic Response of Liver Cells to Partial Hepatectomy
Authors: Jahiel Rene I. , Taylor David , Rainford Norbert , Hirschberg Stephen E. , Kroman Rayna
Published: May 2006

Partially hepatectomized mice were injected with inducers of interferon, and the mitotic activity of liver cells was measured. The inducers were polyriboinosinic·polyribocytidylic acid, poly(I·C), Newcastle disease virus, and statolon. Each inhibited the mitosis of liver cells. Poly(I·C) was effective in doses as low as 1 μg per mouse. Polyriboinosinic acid, poly(I), had no inhibitory effect. These results extend the spectrum of action of inducers of interferon to inhibition of mitotic division of an aneoplastic, nonaneuploid mammalian cell.
The Writhing Number of a Space Curve
Authors: Fuller F. Brock
Published: May 2006

A geometric invariant of a space curve, the writhing number, is defined and studied. For the central curve of a twisted cord the writhing number measures the extent to which coiling of the central curve has relieved local twisting of the cord. This study originated in response to questions that arise in the study of supercoiled double-stranded DNA rings.
Ferritin-Conjugated Plant Agglutinins as Specific Saccharide Stains for Electron Microscopy: Application to Saccharides Bound to Cell Membranes
Authors: Nicolson Garth L. , Singer S. J.
Published: May 2006

An electron microscopic stain for specific saccharides was prepared by the conjugation of ferritin to concanavalin A, a plant agglutinin that specifically binds to oligosaccharides containing terminal
d
-glucose,
d
-mannose, or sterically related sugar residues. A technique was developed to allow topological visualization of erythrocyte and other membranes by means of transmission electron microscopy, and the distribution of the binding sites for ferritin-concanavalin A on such membrane preparations was determined. The conjugate was found to bind specifically to the outer, but not the inner, surface of erythrocyte membranes. The number of conjugate molecules bound per unit area of the membrane was larger for rabbit than for human erythrocytes.
Effect of Colicin E3 upon the 30S Ribosomal Subunit of
Escherichia coli
Authors: Senior B. W. , Holland I. B.
Published: May 2006

The properties of 30S ribosomal subunits from untreated and from colicin E3-treated (E3-30S) bacteria have been compared. Polyacrylamide gel electrophoresis of ribosomal proteins revealed no difference, but several studies indicated that the 16S RNA from E3-30S particles was modified. E3-16S RNA showed slightly increased resistance to heat-induced degradation and had a reduced (15 S) sedimentation coefficient on sucrose gradients. Fingerprint analyses of E3-16S RNA revealed that the 3′-terminus of the molecule had been deleted. It was concluded that a primary effect of colicin E3 is the activation of a highly specific RNase that degrades 30S ribosomal RNA
in situ
, and that the resulting fragment(s) are probably retained within the 30S particle.
A Unique Synaptosomal Fraction, Which Accumulates Glutamic and Aspartic Acids, in Brain Tissue
Authors: Wofsey Alan R. , Kuhar Michael J. , Snyder Solomon H.
Published: May 2006

Subcellular fractionation of rat cerebral cortical slices on sucrose density gradients provides evidence for the existence of a unique synaptosomal fraction (enriched in pinched-off nerve endings) that selectively accumulates glutamic and aspartic acids. The particles in this fraction sediment to a less dense portion of sucrose gradients than do particles that accumulate aromatic, basic, and neutral (large and small) amino acids. Particles that store gamma-aminobutyric acid are even less dense than those that contain exogenous glutamic and aspartic acids. The distribution of endogenous glutamic acid encompasses both that of exogenous glutamic acid and that of the neutral and basic amino acids. These findings provide neurochemical support for the suggestion that glutamic and/or aspartic acid has a specialized synaptic function, perhaps as a neurotransmitter, in the mammalian brain.
In Vitro
Synthesis of Deoxynucleotide Kinase Programmed by Bacteriophage T4-RNA
Authors: Sakiyama Shigeru , Buchanan John M.
Published: May 2006

RNA extracted from T4 phage-infected
Escherichia coli
cells can direct the synthesis of phage-specific deoxynucleotide kinase in a cell-free system from uninfected
E. coli
. The maximum messenger activity is obtained 8 min after infection at 37°C and decreases there-after. The main activity of this messenger RNA has a sedimentation coefficient of about 15 S on a sucrose density gradient. The conditions necessary for the appearance of enzyme activity
in vitro
are the same as those required for
de novo
synthesis of protein. RNA from cells infected with a T4
amber
mutant incapable of inducing the kinase
in vivo
lacks the ability to direct the synthesis of enzyme
in vitro
.
Structure of Concanavalin A at 4.25-Ångström Resolution
Authors: Hardman Karl D. , Wood Mical K. , Schiffer Marianne , Edmundson Allen B. , Ainsworth Calinton F.
Published: May 2006

An electron density map produced by x-ray diffraction analysis of concanavalin A has been calculated to 4.25 Å from data of three isomorphous heavy atom derivatives. The crystals are orthorhombic, with unit-cell dimensions of 63.1, 87.0, and 89.2 Å for
a, b
, and
c
, respectively. The space group is I222, with eight asymmetric units per unit cell. The crystal asymmetric unit contains 27,000 daltons of protein and reflects the chemically unique component (protomer) within the oligomer. Separate chemical studies indicate that the protomer consists of two different polypeptide chains. Four protomers cluster around the intersection of three mutually perpendicular two-fold rotation axes to form a molecule of 108,000 daltons. The molecule can also be subdivided into two-protomer units of 54,000 daltons. Within the two-protomer unit, there are significantly more contacts joining the protomers than there are
between
adjacent two-protomer units that form the total molecule. These results provide a possible explanation for disagreement in molecular weights obtained in previous ultracentrifugal studies.
Regulation of Formation and Proposed Structure of the Factor Inhibiting the Release of Melanocyte-Stimulating Hormone
Authors: Celis María E. , Taleisnik S. , Walter Roderich
Published: May 2006

Microsomal preparations from the stalk median eminence of female rats are shown to contain an enzymic activity that is responsible for the formation of MSH-release-inhibiting factor (MSH-R-IF). The amount of this activity remains constant throughout the estrous cycle. The corresponding mitochondrial preparations from the stalk median eminence contain another enzymic principle, estrous cycle-dependent, which competes with the enzyme present in the microsomal preparation for the same “substrate”, and can thereby prevent the formation of MSH-R-IF.

Several neurohypophyseal hormones, analogs, and peptide intermediates have been tested for their intrinsic MSH-R-IF activity and for their ability to be transformed into MSH-R-IF by incubation with microsomal preparations of stalk median eminence from male rats; it is concluded that the enzyme responsible for the formation of MSH-R-IF is an exopeptidase and that the release-inhibiting factor itself is a tripeptide. Oxytocin is converted by the incubation to
L
-prolyl-
L
-leucylglycinamide; nanogram amounts of this tripeptide inhibit the release of MSH from the pituitary both
in vivo
and
in vitro
.
Stereological Measurements of Cardiac Ultrastructures Implicated in Excitation-Contraction Coupling
Authors: Page Ernest , McCallister L. P. , Power B.
Published: May 2006

Electron micrographs of osmium-fixed left ventricles from 200-g female rats were analyzed by stereological techniques. By the use of equations developed by H. Sitte it was possible to determine volume fractions of organelles and absolute membrane areas per unit cell volume for cellular membrane systems implicated in excitation-contraction coupling. The fractions of cell volume were: mitochondria 0.34, myofibrils 0.481, T-system 0.012, total sarcotubules 0.035, other 0.13. The membrane areas per unit cell volume (μm
2
/μm
3
) were: external sarcolemma 0.27, external sarcolemma + T-system 0.34, total sarcotubules 1.3. Diads made up 0.08 of sarcotubular volume and 0.12 of sarcotubular membrane area. 0.14 of the external sarcolemmal membrane area was involved in diadic complexes with underlying subsarcolemmal cisterns.
Soluble Complexes between Steroid Hormones and Target-Tissue Receptors Bind Specifically to Target-Tissue Chromatin
Authors: Steggles A. W. , Spelsberg T. C. , Glasser S. R. , O'Malley B. W.
Published: May 2006

Cytoplasmic fractions containing steroid hormone receptor were prepared from rat prostate and uterine tissues, incubated first with [
3
H]dihydrotestosterone or [
3
H]estradiol, and then with their respective target and non-target tissue chromatins. Only prostate and testis chromatin bound the dihydrotestosterone-receptor complex from prostate cytosol extensively. Similarly, uterine chromatin bound more estradiol-receptor complex from uterus than did liver, spleen, or lung chromatin. Complexes between dihydrotestosterone or estradiol with cytosols prepared from liver and spleen bound less extensively, and similarly, to all chromatins. Analogous results are described for the [
3
H]progesterone-receptor complex from chick oviduct cytosol binding to oviduct chromatin. These studies suggest that the chromatin of all steroid hormone target tissues may contain “acceptor sites” for their respective hormone-receptor complexes, and are thus programmed to receive the complex as it is transferred into the nucleus from the cytoplasm of the cell.
Nature and Self-Regulated Synthesis of the Repressor of the
hut
Operons in
Salmonella typhimurium
Authors: Smith Gerald R. , Magasanik Boris
Published: May 2006

The enzymes mediating histidine utilization, coded by the
hut
genes, in
Salmonella typhimurium
are synthesized from two closely-linked operons. Results presented in this paper show that these operons are regulated by a single repressor protein. The
hutC
gene, coding for this repressor, is part of one of the operons. Since this same operon is sensitive to the repressor, the repressor apparently represses its own synthesis.
Lipopolysaccharide and Aldoheptose Biosynthesis in Transketolase Mutants of
Salmonella typhimurium
Authors: Eidels L. , Osborn M. J.
Published: May 2006

Genetic and biochemical evidence that sedoheptulose-7-phosphate is an obligatory precursor of the L-glycero-D-mannoheptose residues of the lipopolysaccharide of
Salmonella
was obtained by isolation and characterization of transketolase-negative mutants of
Salmonella typhimurium
. These mutants, which are defective in synthesis of sedoheptulose-7-phosphate, were found to produce an incomplete heptose-deficient lipopolysaccharide, and were also sensitive to bile salts, a characteristic property of heptose-deficient mutants. Phenotypic repair of the defect in lipopolysaccharide synthesis was obtained by addition of exogenous sedoheptulose-7-phosphate to growing cultures of the mutant strains. Characterization of revertants isolated either as transketolase-positive or heptose-positive provided further evidence that the heptose deficiency resulted from mutation at the transketolase locus. On the basis of these findings a possible pathway for conversion of sedoheptulose-7-phosphate to L-glycero-D-mannoheptose is proposed.
Proteins from Plant Cell Walls Inhibit Polygalacturonases Secreted by Plant Pathogens
Authors: Albersheim Peter , Anderson Anne J.
Published: May 2006

Proteins extracted from the cell walls of Red Kidney bean hypocotyls, tomato stems, and suspension-cultured sycamore cells can completely inhibit the activity of the polygalacturonases (polygalacturonide hydrolases, EC 3.2.1.15) secreted by the fungal plant pathogens
Colletotrichum lindemuthianum, Fusarium oxysporum
, and
Sclerotium rolfsii
. The inhibitor of the
C. lindemuthianum
polygalacturonase, purified 560-fold from bean hypocotyl extracts, is 40 times as effective an inhibitor of the
C. lindemuthianum
polygalacturonase as of the
F. oxysporum
polygalacturonase, and does not demonstrably inhibit the
S. rolfsii
polygalacturonase. A crude hypocotyl extract that completely inhibits the three polygalacturonases does not inhibit
C. lindemuthianum
-secreted cellulase, xylanase, α-galactosidase, α-arabinofuranosidase, or α-galacturonosidase. The purified bean hypocotyl protein combines with the
C. lindemuthianum
polygalacturonase to form a complex with a dissociation constant of 2 × 10
-9
M or less. The physical properties of these inhibitors are similar to those of phytohemagglutinins and of the plant glycoproteins capable of agglutinating transformed animal cells.
Control of Plasmid Replication in
Escherichia coli:
Correlation of the Membrane Site of DNA Replication with the Bacterial Segregation Unit
Authors: Korn D. , Thomas M.
Published: May 2006

The fate of parental λ genomes after superinfection of homoimmune lysogenic cells was studied. The data confirm a previous observation that in the presence of the λ repressor, superinfecting λ DNA does not become associated with replication sites on the bacterial cell membrane. Under these conditions, the nonreplicating, superinfecting phage genomes do not become associated with the bacterial segregation unit. These results support the concept that the attachment of DNA to the bacterial membrane at specific sites is involved in the control of both chromosome replication and segregation, as predicted by the replicon hypothesis.
The Control of Morphogenesis: An Enzymatic Mechanism for the Initiation of Septum Formation in Yeast
Authors: Cabib Enrico , Farkas Vladimir
Published: May 2006

Previous work with yeast has indicated that chitin is the specific component of the septum between mother and daughter cell. Experiments with synchronized cells show that chitin synthesis is initiated at a precise time in the cell cycle. Newly discovered features of the chitin synthetase system suggest how this specificity in location and timing can be achieved. The particulate chitin synthetase is shown to exist almost entirely in an inactive or zymogen state. The zymogen can be converted into an active form either by an enzyme (activating factor) present in yeast or by trypsin. The activating factor is found in a particulate fraction, but can be solubilized by mild sonic oscillation. A heat-stable protein, previously isolated from yeast and believed to inhibit chitin synthetase, has now been found to act as an inhibitor of the activating factor to which it binds very tightly. It is proposed that chitin synthetase, in the zymogen form, is uniformly distributed on the cytoplasmic membrane. At the time of septum initiation, vesicles carrying the activating factor would be directed to specific sites and bring about the localized conversion of the zymogen into the active form. A molecular model is thus introduced for processes of morphological change and differentiation.
Cell Fractionation and Arrangement on Fibers, Beads, and Surfaces
Authors: Edelman G. M. , Rutishauser U. , Millette C. F.
Published: May 2006

A new method, fiber fractionation, has been used to isolate and separate cells. The cells are adsorbed to fibers covalently coupled to molecules such as antigens, antibodies, and lectins which can bind specifically to cell-surface components. The cells are then removed mechanically by plucking the taut fibers. Alternatively, competitive inhibitors of binding may be used to remove the cells at a lesser rate. Successful fractionations have been achieved by varying the degree of derivatization of the fibers by the lectin concanavalin A. Lymphoid cells have been separated by the use of different antigens coupled to the fibers. The method may also be used for specific fixation and manipulation of viable cell populations in culture. In addition to fibers, beads and surfaces have been specifically derivatized and used to achieve different geometrical arrangements of the cells.
Characterization of the J Chain from Polymeric Immunoglobulins
Authors: Morrison Sherie L. , Koshland Marian Elliott
Published: May 2006

The J chains isolated from polymeric IgA and IgM were shown to be distinct from the other immunoglobulin subunits, including the secretory component, both on the basis of amino-acid content and antigenic determinants. By the same criteria, the J chains were found to be indistinguishable from each other whether they were derived from pentamer IgM, polydisperse myeloma IgA, or dimer colostral IgA. The only differences were observed in (
a
) the extent of disulfide bond cleavage required for J chain release from the different polymers, and (
b
) the three-dimensional arrangement of J chains in the different polymers. These data support the hypothesis that the same J chain joins the monomeric units of IgA and IgM to form their respective polymeric molecules.
Adenosine Triphosphatase Associated with Adenosine Triphosphate-Dependent Deoxyribonuclease
Authors: Nobrega F. G. , Rola F. H. , Pasetto-Nobrega M. , Oishi M.
Published: May 2006

An ATPase activity that is completely dependent on DNA is associated with the ATP-dependent DNase (
recB-recC
enzyme) purified from
Escherichia coli
. There is a strong correlation between the ATPase and the DNase activities under various assay conditions. With
E. coli
DNA as substrate, 8-9 molecules of ATP are hydrolyzed to ADP and inorganic phosphate for every phosphodiester bond hydrolyzed by the DNase. The possible functional relationship of the ATPase and DNase activities is discussed.
Growth Inhibition of Sympathetic Cells by Some Adrenergic Blocking Agents
Authors: Angeletti Pietro U. , Levi-Montalcini Rita
Published: May 2006

Treatment of newborn mice and rats with the adrenergic blocking agents, guanethidine and bretylium tosylate, results in massive destruction of immature sympathetic nerve cells. A growth inhibition of the same cells is caused by reserpine. Similarities and differences between the effects elicited by these three ganglion blocking agents and a dopamine analog, 6-hydroxydopamine, are discussed.
Intermolecular Interaction Effects in the Amide I Vibrations of β Polypeptides
Authors: Krimm S. , Abe Yasuaki
Published: May 2006

Previous perturbation treatments of the Amide I vibrations of β polypeptides are inconsistent with a detailed normal coordinate analysis of crystalline polyglycine I. This analysis indicates that the
D
10
interaction constant is essentially zero, rather than the large value (about 20 cm
-1
) required by the earlier application of the perturbation theory. It is suggested that the previously neglected
D
11
term should be included in the perturbation expression, and it is shown that the physical origin of such a term can be accounted for by transition dipole coupling. This mechanism is shown to give a reasonable explanation of splittings of the C=O stretching vibrations in hydrogenbonded carboxylic acid dimers. Its application to β polypeptides provides a satisfactory interpretation of splittings in the Amide I modes.
Distribution of Saccharide Residues on Membrane Fragments from a Myeloma-Cell Homogenate: Its Implications for Membrane Biogenesis
Authors: Hirano Hiroshi , Parkhouse Brenda , Nicolson Garth L. , Lennox Edwin S. , Singer S. J.
Published: May 2006

Ferritin conjugates of two plant agglutinins, concanavalin A and ricin, have been used as specific electron microscopic stains for covalently-bound saccharide residues on membrane fragments from a myeloma-cell homogenate. The results indicate that different saccharide residues are uniformly localized to a single surface of each membrane fragment. In particular, the ferritin-concanavalin A conjugate binds exclusively to the cisternal side of membrane fragments of the rough endoplasmic reticulum. If it is postulated that the biogenesis of eukaryotic plasma membranes involves an assembly-line process from precursor intracellular membranes, these observed asymmetric distributions of saccharides on cell membranes can be explained.
Nucleic Acid Hybridization with RNA Immobilized on Filter Paper
Authors: Saxinger W. C. , Ponnamperuma C. , Gillespie D.
Published: May 2006

RNA has been immobilized in a manner suitable for use in molecular hybridization experiments with dissolved RNA or DNA by a nonaqueous solid-phase reaction with carbonyldiimidazole and RNA “dry coated” on cellulose or, preferably, on previously activated phosphocellulose filters. Immobilization of RNA does not appear to alter its chemical character or cause it to acquire affinity for unspecific RNA or DNA. The versatility and efficiency of this method make it potentially attractive for use in routine analytical or preparative hybridization experiments, among other applications.
A Molecular Basis for Learning and Memory
Authors: Kosower Edward M.
Published: May 2006

Three stages in memory (electrical, short-term and long-term) are reviewed. The short computing time of organized neural systems favors synapses as loci for storage of memory. Transfer of neuronal excitation depends upon transfer of transmitter, involving the steps: vesicle attachment to presynaptic vesicle-release sites, contraction at dithiolate structures of these sites, exocytosis of transmitter, movement of transmitter across synaptic cleft, and reception at postsynaptic sites. Disulfide formation from dithiolates (calcium dithiolate salt) occurs during excitation and can represent a short-term alteration in properties of vesicle-release sites and, thus, short-term memory. Repair by one mechanism of the altered vesicle-release sites through reduction of the disulfide bond returns the system to its original state or, by a second mechanism, enlarges the presynaptic area covered by these sites. Such enlargement is a stable, permanent mode: long-term memory. Suitable concentrations of transmitter at postsynaptic receptor sites lead to mobilization of additional receptor sites through polymerization of monomeric receptor units. Postsynaptic expansion constitutes a metastable long-term storage, readily reconstituted under appropriate stimuli. Reverberations at the electrical stage of memory are suggested as a necessary link to the chemical stage of memory. These ideas constitute the elements of a molecular theory of learning and memory.
Degradation of DNA RNA Hybrids by Ribonuclease H and DNA Polymerases of Cellular and Viral Origin
Authors: Keller Walter , Crouch Robert
Published: May 2006

Ribonuclease H from human KB cells, chick embryos, calf thymus, avian myeloblastosis virus, and Rous associated virus specifically degrades the RNA of DNA·RNA hybrids, producing mono- and oligoribonucleotides terminated in 5′-phosphates. The cellular RNase H is an endonuclease, whereas the viral enzyme appears to be an exonuclease. Viral DNA polymerase and RNase H copurify through all separation steps. Therefore, RNase H activity is an intrinsic part of the viral DNA polymerase. DNA·RNA hybrids are also degraded by nucleases associated with cellular DNA polymerases and by exonuclease III. However, these nucleases differ from RNase H in their ability to degrade
both
strands of DNA·RNA hybrids.
Enzymic Depolymerization of Macromolecular Heparin as a Factor in Control of Lipoprotein Lipase Activity
Authors: Horner Alan A.
Published: May 2006

Macromolecular heparin from rat skin shows poor lipoprotein lipase-releasing activity
in vivo
and is a potent inhibitor of rat-heart lipoprotein lipase
in vitro
. Rat-skin heparin is depolymerized by incubation with the 100,000 ×
g
supernatant from a sonicated homogenate of rat small intestine. The depolymerized products, fractionated by gel filtration, range from inhibitors to activators of lipoprotein lipase as molecular size decreases. Depolymerized rat heparin in the same molecular size range as commercial heparin from pig intestinal mucosa has about two-thirds the activity of the commercial preparation, both
in vivo
and
in vitro
.
The Thiol Group in the Catalytic Chains of Aspartate Transcarbamoylase
Authors: Evans David R. , McMurray Cecil H. , Lipscomb William N.
Published: May 2006

The allosteric enzyme aspartate transcarbamoylase (EC 2.1.3.2) was previously shown to consist of two functionally distinct types of polypeptide chains. X-ray diffraction and chemical studies showed that there are six copies of both catalytic (C) and regulatory (R) chains, and that the intact molecular complex (C
6
R
6
) has D
3
symmetry. Organomercurials react preferentially with the four thiol groups on each R chain, dissociating the molecular complex. We show that 2-chloromercuri-4-nitrophenol reacts specifically and rapidly with the single C-chain thiol, which is believed to be near the catalytic site. This reaction inactivates the enzyme in solution and does not dissociate the molecular complex. Spectrophotometric titration and mercury analysis indicates that six molecules of this mercurial are firmly bound to the enzyme (R
6
C
6
), and crystallographic studies establish that only six sites, related by D
3
symmetry, are modified.

The known low reactivity of this C-chain thiol with other sulfhydryl reagents, the unusual structural requirements in the reaction with 2-chloromercuri-4-nitrophenol, and the spectral properties of the resulting derivative provide insight into the environment of this thiol. Probably, at least one positively charged group of the enzyme is nearby, and the environment of this thiol is at least partially hydrophobic.
Partial Duplication in the “Hinge” Region of IgA
1
Myeloma Proteins
Authors: Frangione Blas , Wolfenstein-Todel Carlota
Published: May 2006

The aminoacid sequence of the “hinge” region of two human IgA
1
myeloma proteins was found to be identical. A 30-residue fragment contains 3 cysteines, 12 prolines, and carbohydrate, and the sequence of a small segment of the hinge region is repeated at least twice. Since a deletion of 12-13 residues was found in the same region of an IgA
2
myeloma protein, it is possible that IgA
1
molecules are the result of the insertion of a partially duplicated gene segment in the immunoglobulin genes.
Amino-Acid Sequence of Rabbit Skeletal Tropomyosin and Its Coiled-Coil Structure
Authors: Sodek J. , Hodges R. S. , Smillie L. B. , Jurasek L.
Published: May 2006

A tentative amino-acid sequence for the COOH-terminal half of rabbit skeletal tropomyosin is reported. These studies confirm our previous conclusions that this tropomyosin consists of several different but similar polypeptide chains. In the sequence, nonpolar residues occur in two series at intervals of seven residues. Amino-acid residues in series I are three residues on the NH
2
-terminal side of, and four residues on the COOH-terminal side of, residues in series II. The presence of occasional charged or ambivalent residues in the positions of series I or II does not lead to a disruption of this long-range pattern. The majority of residues located between the nonpolar residues are charged or polar amino acids. Two highly similar or identical α-helices with the reported sequence can be packed together in parallel in a coiled-coil structure. These may be in register or staggered by seven residues or some multiple of it. The observation that groups of small hydrophobic side chains appear to alternate with groups of bulky side chains suggests that a staggered arrangement of the two α-helices would maximize the regularity and hydrophobic interactions of the coiled-coil. Model building considerations show that this would occur with a stagger of 14 residues. Such an arrangement could account for the end-to-end aggregation of tropomyosin in solution, and in crystal and tactoid filaments. However, a structure in which the two polypeptides are in register cannot be ruled out.
Degradation of Abnormal Proteins in
Escherichia coli
Authors: Goldberg Alfred L.
Published: May 2006

Evidence is presented that
E. coli
contains a mechanism for selective degradation of abnormal proteins. Unfinished polypeptides containing puromycin, proteins containing frequent errors in translation, such as those synthesized by strains containing a
ram
mutation or a missense suppressor, and proteins containing amino-acid analogs were degraded more rapidly than were normal cell proteins. The degradation of analog- or puromycin-containing proteins appears to be an energy-dependent process. Unlike normal proteins, such proteins were degraded at similar rates by growing and by nongrowing cells.
Parasexual Recombination in
Dictyostelium discoideum:
Selection of Stable Diploid Heterozygotes and Stable Haploid Segregants
Authors: Katz E. R. , Sussman M.
Published: May 2006

Haploid strains of
Dictyostelium discoideum
bearing temperature-sensitive mutations have been used to select stable diploid, heterozygotic clones, which arise at low frequency (about 10
-5
). Segregants arise from such diploids at low frequency (about 10
-3
). The diploids were heterozygous for resistance to cycloheximide and were phenotypically sensitive to the drug. Growth of the diploid cells in the presence of cycloheximide automatically selected those segregants bearing the resistant allele, and facilitated examination of the assortment of unselected markers. The combination of the two selective methods provides a workable system of genetic analysis in this species. We have used this method to locate six markers on three different linkage groups.
Bacteriophage T7 DNA Replication: A Linear Replicating Intermediate
Authors: Wolfson John , Dressler David , Magazin Marilyn
Published: May 2006

The T7 chromosome in the first round of replication is a Y-shaped DNA rod. Thus, it differs from previously observed bacterial and viral replicating chromosomes that are circular.
Evidence for Translation of Viral-Specific RNA in Cells of a Mouse Mammary Carcinoma
Authors: Axel R. , Schlom J. , Spiegelman S.
Published: May 2006

A procedure is described permitting the detection of viral-specific RNA in a mouse mammary tumor. The method involves molecular hybridization with radioactively labeled DNA complementary to the RNA of the mouse mammary-tumor virus. RNA homologous to that of the mammary agent has been found in both the nuclear and polyribosomal fractions of tumor cells. The results imply that the oncogenic information is serving as messenger RNA that directs the synthesis of proteins required for virus production, and perhaps for the maintenance of the neoplastic state. The technology developed is immediately applicable to tumors of human origin.
Effect of Corticotropin and Desglycinamide
9
-Lysine Vasopressin on Suppression of Memory by Puromycin
Authors: Lande Saul , Flexner Josefa B. , Flexner Louis B.
Published: May 2006

The puromycin-induced blockade of expression of maze learning in mice can be prevented by subcutaneous administration of “Purified Cortrophin Gel” up to 3 days prior to training. A similar protective effect was not found when highly purified corticotropin was tested, but was observed after administration of desglycinamide
9
-lysine vasopressin. It appears that pressorpeptides are more potent protective agents than corticotropin when administered subcutaneously, and that vasopressin contamination of the commercial preparation was probably responsible for the protective effects previously reported. These experiments suggest that vasopressin and its congeners modify memory consolidation in such a way that the “expression” of memory becomes insensitive to puromycin.
Structure of a Calcium-Binding Carp Myogen
Authors: Nockolds Clive E. , Kretsinger Robert H. , Coffee Carole J. , Bradshaw Ralph A.
Published: May 2006

The amino-acid sequence and three-dimensional structure of a calcium-binding protein prepared from carp muscle has been determined. This protein, designated carp-muscle calcium-binding protein B, is one of three closely related parvalbumins found in this tissue. The electron density map, calculated by heavyatom substitution crystallographic methods to 2.0-Å resolution, reveals the orientation of most of the amino-acid side chains. The calcium coordination site consists of one glutamic- and three aspartic-acid carboxyl groups in a tetrahedral arrangement. The core of this spherical molecule is remarkably hydrophobic, with 8 of its 10 phenylalanine side chains packed in an approximate herringbone pattern. 52 of the 108 residues are in six α-helixes; there is no β-pleated sheet. The acetylated amino-terminal alanine appears not to be accessible to solvent. All of the heavy-atom derivatives are bound at the sole cysteine. The properties of this protein suggest a relationship to troponin A of mammalian tissue.
Increased Uptake of Amino Acids and 2-Deoxy-D-Glucose by Virus-Transformed Cells in Culture
Authors: Isselbacher K. J.
Published: May 2006

Transformed and nontransformed cells in tissue culture differ in their rate of uptake of certain nutrients, as determined by a polyester-coverslip technique. A 2.5- to 3.5-fold increased rate of uptake of α-aminoisobutyric acid, cycloleucine, and 2-deoxy-D-glucose was observed with polyoma virus-transformed baby hamster kidney (BHK) 21 cells and simian virus 40 (SV40)-transformed BALB/3T3 (mouse fibroblast) cells, compared to their nontransformed counterparts. Kinetic analysis suggested that the increased uptake by cells transformed with virus was associated with a 3-fold greater
V
max
, with no detectable changes in apparent
K
m
. Limited studies also revealed increased initial rates of uptake by murine sarcoma virus-transformed rat liver cells, as compared to the parental line. Exposure of cells to concanavalin A and wheat-germ agglutinin led to significant reductions in amino-acid uptake by both transformed and nontransformed cells; however, transformed cells showed a greater decrease in uptake after exposure to wheat-germ agglutinin. Increased initial rates of uptake of certain amino acids and sugars may be a feature common to transformed cells, compared to their parental control.
Replication of Mitochondrial DNA. Circular Replicative Intermediates in Mouse L Cells
Authors: Robberson Donald L. , Kasamatsu Harumi , Vinograd Jerome
Published: May 2006

The frequency, composition, and structure of circular replicating forms of mitochondrial DNA, including two new forms described here, suggest a scheme for the mode of replication of this DNA.
Pyrimidine Sequences from the DNA of Bacteriophages fd, fl, and ϕX174
Authors: Ling V.
Published: May 2006

By the use of techniques previously developed to determine the sequence of large, unique pyrimidine oligonucleotides in bacteriophage fd DNA, pyrimidine sequences in the related phage fl and the unrelated phage ϕX174 amber 3 were determined. The DNA of fl contains many pyrimidine sequences completely identical to those in fd, including one sequence of 20 base residues. The large pyrimidine oligonucleotides in ϕX174 DNA are quite different from those in fd, although some homology is observed. There is present in each of the phage DNAs a pyrimidine oligonucleotide rich in thymidine that contains a common sequence of C_T_T_T_T_T_T_T.