bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in the three-dimensional structure of concanavalin A upon demetallization
Authors: Reeke George N. , Becker Joseph W. , Edelman Gerald M.
Published: May 2006

When the Mn
2+
and Ca
2+
ions normally present in concanavalin A are removed, the protein becomes incapable of binding saccharides. To explore the structural differences between the native and demetallized forms and their effects on the saccharide-binding properties of the protein, we have refined and compared the crystal structures of both forms. Refinement, carried out by automated difference Fourier methods, has revealed a number of differences between the two structures as well as minor differences between the two crystallographically independent monomers in the demetallized structure. Significant differences between the holo- and apoproteins are confined to the region where the metals are bound. These differences include a reorganization and disordering of the loop, consisting of residues 7-25, that contains all of the direct metal ligands of the protein. In some molecules, the side chain of arginine-228 appears to move into the metal-binding region, possibly compensating in part for the absence of the metal's positive charge. The
cis
peptide observed in the native protein at alanine-207 is apparently not present in the demetallized protein. The conformational differences affect many of the residues currently thought to be involved in the specific binding of saccharides.
Participation of histocompatibility antigens in capping of molecularly independent cell surface components by their specific antibodies
Authors: Bourguignon Lilly Y. W. , Hyman Robert , Trowbridge Ian , Singer S. J.
Published: May 2006

The antibody-induced capping of several cell surface components has been investigated by immunofluorescence methods using two mouse cell lines, a parental C58 thymoma line and a mutant derived from it lacking TL and H-2 antigens. Other cell surface components were present in approximately equal amounts on the two cells. Parental cells treated with rabbit antibodies to T200, a major surface glycoprotein, rapidly formed caps containing T200, but the mutant cells similarly treated showed a uniform surface distribution of T200. On the other hand, with a secondary antibody treatment, the T200 on both cells capped equally well. When the indirect T200 caps were examined using a second immunofluorescent stain for H-2, TL, or Thy-1 antigens, it was found that on parental cells all three of these antigens were co-capped with T200; on mutant cells no staining was found for H-2 or TL, as expected, and essentially uniform distribution of Thy-1 was observed. The co-capping of H-2, TL, and Thy-1 antigens with T200 on the parent cell is remarkable, because the first three components are known to be molecularly independent in lymphocyte cell surfaces. The indirect capping of the viral glycoprotein gp 69/71 similarly induced a co-capping of H-2 and TL antigens on the parent cell. These results demonstrate that H-2 and related molecules may co-cap with a variety of independent cell surface antigens. Such co-capping of histocompatibility components could play an important role in a proposed dual recognition mechanism for cell-mediated cytotoxicity reactions and other immunologically important cell-cell interactions.
Rescue of immunoglobulin secretion from human neoplastic lymphoid cells by somatic cell hybridization.
Authors: Levy R , Dilley J
Published: May 2006

B leukemia cells from four different patients were hybridized with a mouse myeloma cell line with polyethylene glycol as a fusing agent. The original leukemia cells all expressed immunoglobulin on their surface, but failed to secrete it. Over 200 different human-mouse somatic cell hybrids were obtained; 57% of them secreted human immunoglobulin in large amounts. Human immunoglobulin secretion can be a stable property of these hybrid cells over months of continuous culture. In each case the human immunoglobulin secreted was restricted to the light chain type expressed by the parental B leukemia cell. In addition, these hybrid cells secreted the original mouse myeloma protein and a variety of mixed human-mouse immunoglobulin molecules.
Studies on the murine Ss protein: demonstration that the Ss protein is functionally the fourth component of complement.
Authors: Carroll M C , Capra J D
Published: May 2006

This report describes a simple and reproducible assay for the fourth component of murine complement (C4). Utilizing this assay, experiments are described which conclusively demonstrate that the murine Ss protein (serum substance) is functional C4 and that ascitic fluid may be used as a source for isolating Ss. The evidence that Ss is functional C4 is: (i) pretreatment of mouse plasma with F(ab')2 anti-Ss completely abrogated the C4 hemolytic titer; and (ii) in the isolation of the Ss protein from ascitic fluid, Ss immunochemical activity and C4 functional activity coeluted in each step of a four-step purification procedure.
Visualization of central noradrenergic neurons in thick sections by the unlabeled antibody method: a transmitter-specific Golgi image.
Authors: Grzanna R , Molliver M E , Coyle J T
Published: May 2006

The unlabeled peroxidase-antiperoxidase method has been used with an antiserum against rat dopamine-beta-hydroxylase (DBH) to obtain a three-dimensional image of noradrenergic cell bodies and their processes in thick Vibratome sections of rat brain. This method stains DBH-positive neurons exclusively with a result similar to that of the Golgi method, which makes it possible to analyze the geometric plan of these neurons and their projections in the central nervous system. In 100-micron sections, DBH-positive axons can be followed over long distances, and the results indicate that their distribution in cerebral and cerebellar cortex is not diffuse but has a strict geometric order.
High accuracy finite difference approximation to solutions of elliptic partial differential equations
Authors: Lynch Robert E. , Rice John R.
Published: May 2006

A flexible finite difference method is described that gives approximate solutions of linear elliptic partial differential equations,
Lu
=
G
, subject to general linear boundary conditions. The method gives high-order accuracy. The values of the unknown approximation function
U
are determined at mesh points by solving a system of finite difference equations

L
h
U

=

I
h
G. L
h
U

is a linear combination of values of
U
at points of a standard stencil (9-point for two-dimensional problems, 27-point for three-dimensional) and

I
h
G

is a linear combination of values of the given function
G
at mesh points as well as at other points. A local calculation is carried out to determine the coefficients of the operators

L
h

and

I
h

so that the approximation is exact on a specific linear space of functions. Having the coefficients of each difference equation, one solves the resulting system by standard techniques to obtain
U
at all interior mesh points. Special cases generalize the well-known 0(
h
6
) approximation of smooth solutions of the Poisson equation to 0(
h
6
) approximation for the variable coefficient equation -div(
p
grad[
u
]) +
Fu
=
G
. The method can be applied to other than elliptic problems.
Mode of action of colicin Ia: effect of colicin on the Escherichia coli proton electrochemical gradient.
Authors: Tokuda H , Konisky J
Published: May 2006

By use of the technique of flow dialysis, the membrane potential (deltapsi) and pH gradient (deltapH) have been measured in colicin Ia-treated Escherichia coli K-12 cells and in membrane vesicles prepared from such cells. Although such cells and vesicles are able to generate a transmembrane deltapH at pH 5.5, they do not generate a transmembrane deltapsi. Glucose-6-phospate uptake by cells is shown to be stimulated at pH 5.5 and inhibited at pH 7.5 by colicin Ia treatment. On the other hand, proline uptake is demonstrated to be inhibited progressively at pH 5.5, 6.6, and 7.5 in colicin Ia-treated cells. These data provide strong evidence for a colicin Ia-induced membrane deplorization and indicate that the membrane becomes permeable to ion(s) other than protons after treatment with colicin Ia.
"Nonspecific" cholinesterase and acetylcholinesterase in rat tissues: molecular forms, structural and catalytic properties, and significance of the two enzyme systems.
Authors: Vigny M , Gisiger V , Massoulié J
Published: May 2006

"Nonspecific" cholinesterase (acylcholine acylhydrolase; EC 3.1.1.8) from various rat tissues has been found to exist in several stable molecular forms that appear as exact counterparts of molecular forms of acetylcholinesterase (acetylcholine hydrolase; EC 3.1.1.7). The sedimentation pattern of cholinesterase was similar to that of acetylcholinesterase with a small but significant shift between the sedimentation coefficients of the corresponding forms. Extraction yields in different media also demonstrated a close parallelism between the two enzyme systems. Other properties, such as thermal stability and catalytic characteristics, indicated both differences and similarities. In spite of the structural resemblance implied by their physicochemical properties, cholinesterase did not crossreact with antibodies against acetylcholinesterase. The nature of the relationships revealed by these studies and their bearing on the physiological significance of cholinesterases are discussed.
Isolation and characterization of a highly repetitious inverted terminal repeat sequence from Oxytricha macronuclear DNA.
Authors: Herrick G , Wesley R D
Published: May 2006

The low-complexity "gene-sized" linear DNA duplexes of the Oxytricha macronucleus sport short inverted terminal repeats; thus, each single strand is capable of forming a circle held together by a duplex "neck" [Wesley, R. D. (1975) Porc. Natl. Acad. Sci. USA 72, 678--682]. We have isolated necks from total, circularized, single-stranded macronuclear DNA by treatment with nuclease S1. Necks represent at least 2.2% of the total DNA, are homogeneous in size (23 base pairs), melt at 55 degrees in 0.18 M Na+, and reassociate extremely rapidly at 22 degrees (Cot1/2 = 1.1 X 10(-5) mol-liter-1.sec) to form hybrid necks of the same thermal stability. From these and other results, we conclude that all necks on all the many thousands of different single-stranded circles are the same. The neck sequence is therefore highly repetitious--found in multiple copies (as inverted terminal repeats at flush duplex ends and probably also internally) on each natural "gene-sized" macronuclear DNA molecule--implying the possible participation of this sequence both in the general vegetative metabolism of macronuclear DNA and in the pre-vegetative process whereby macronuclear DNA is excised from the total Oxytricha genome.
Amino-terminal sequence analysis of the structural proteins of Sindbis virus.
Authors: Bell J R , Hunkapiller M W , Hood L E , Strauss J H
Published: May 2006

The structural proteins of Sindbis virus, an enveloped virus which belongs to the Togavirus family, have been subjected to automated Edman degradation using improved techniques. Extensive NH2-terminal sequences of about 50 residues were determined for each of the two membrane glycoproteins. In both cases the NH2 terminus of the molecule was found to be similar in composition to typical water-soluble proteins. The viral capsid protein was found to have a blocked alpha-amino group. This is consistent with other observations that viral proteins derived from the NH2 terminus of precursor molecules are often blocked.
Genetic analysis of the G1 period: Isolation of mutants (or variants) with a G1 period from a Chinese hamster cell line lacking G1
Authors: Liskay R. Michael , Prescott David M.
Published: May 2006

Cells of the Chinese hamster line V79-8 multiply without a G1 period (i.e., they are G1
-
) and have an average generation time of 9.5 hr. After mutagenesis and selection we have derived five stable mutants (or variants) of this line that have longer generation times. In each case the increase in generation time is due solely to the introduction of a G1 period into the cell cycle, with no measurable effect on S, G2, or M. Fusions among these five G1
+
mutant lines and another presumably nonmutant G1
+
line (V79-743) produce hybrid cells lacking a G1 period in all but one case. These complementation tests define five complementation groups among these six G1
+
cell lines. The six G1
+
lines represent five different causes or bases for the presence of a G1 period. The two G1
+
mutants belonging to complementation group V are temperature sensitive for expression of the G1
+
phenotype (G1 ≅ 0, 4, and 6 hr at 33°, 37°, and 39°, respectively). In all cases the G1
-
state is dominant over the G1
+
state, suggesting that the presence of G1 represents a “deficient” condition. Mutants of this type may be useful in the analysis of the switch from G1
-
to G1
+
that occurs normally in cleaving embryos and in elucidation of the genetic mechanism(s) responsible for the presence of a measurable G1 in most cells.
Muscarinic cholinergic receptors in murine lymphocytes: demonstration by direct binding.
Authors: Gordon M A , Cohen J J , Wilson I B
Published: May 2006

Using [3H]quinuclidinyl benzilate as a specific cholinergic muscarinic ligand, it has been demonstrated that lymphocytes have muscarinic binding sites. There are approximately 200 sites per cell and the dissociation constant for quinuclidinyl benzilate is approximately 1 X 10(-9) M. Quinuclidinyl benzilate receptor binding is blocked by atropine and oxotremorine.
Beneficial and detrimental actions of histamine H
1
- and H
2
-receptor antagonists in circulatory shock
Authors: Altura Burton M. , Halevy Simon
Published: May 2006

This study explores the use of both histamine H
1
- and H
2
-receptor antagonists in two different forms of circulatory shock and suggests that histamine may be involved in more than one way in the pathophysiology of circulatory shock. Various single doses of diphenhydramine, chlorpheniramine, promethazine, and burimamide were administered intravenously to Wistar rats subjected to hemorrhagic or bowel ischemia shock. Cumulative survival and mortality, as well as arterial blood pressures and microhematocrits, were monitored. Pretreatment of the animals with the three different H
1
-receptor antagonists exerted significant protection against both forms of shock. Rats pretreated with the H
2
-receptor antagonist, burimamide, demonstrated an exacerbated mortality after induction of shock. Animals pretreated with H
1
-receptor antagonists showed significantly higher mean arterial blood pressure, greater compensatory rebound of blood pressure after induction of shock, and greater responses to transfusion after hemorrhage than control, shocked animals. Similarly, rats pretreated with the H
1
-receptor blockers demonstrated significantly greater compensatory hemodilution which continued late in shock. In marked contrast, rats pretreated with burimamide exhibited opposite effects after hemorrhage and bowel ischemia, i.e., significant falls in blood pressure, lack of compensatory rebound and response to transfusion of shed blood, and a progressive hemoconcentration. This report clearly demonstrates beneficial actions of histamine H
1
-receptor antagonists and detrimental effects of H
2
-receptor antagonists on survival and other parameters in these forms of circulatory shock.
Repeating covalent structure of streptococcal M protein.
Authors: Beachey E H , Seyer J M , Kang A H
Published: May 2006

We have attempted to identify the covalent structure of the M protein molecule of group A streptococci that is responsible for inducing type-specific, protective immunity. M protein was extracted from type 24 streptococci, purified, and cleaved with cyanogen bromide. Seven cyanogen bromide peptides were purified and further characterized. Together, the peptides account for the entire amino acid content of the M protein molecule. Each of the purified peptides possessed the type-specific determinant that inhibits opsonic antibodies for group A streptococci. The primary structures of the amino-terminal regions of each of the purified peptides was studied by automated Edman degradation. The partial sequences of two of the peptides were found to be identical to each other and to that of the uncleaved M protein molecule through at least the first 27 residues. The amino-terminal sequences of the remaining five peptides were identical to each other through the twentieth residue but completely different from the amino-terminal region of the other two peptides. However, the type-specific immunoreactivity and the incomplete analysis of the primary structure of the seven peptides suggest that the antiphagocytic determinant resides in a repeating amino acid sequence in the M protein molecule.
Expression of hydrogenase activity in free-living
Rhizobium japonicum
Authors: Maier Robert J. , Campbell Norman E. R. , Hanus Frank J. , Simpson Frank B. , Russell Sterling A. , Evans Harold J.
Published: May 2006

A medium is described on which selected
Rhizobium japonicum
strains express hydrogenase (H
2
uptake) activity under free-living conditions. Low concentrations of carbon substrates, decreased oxygen tension, and the quantity of combined nitrogen in the medium were major factors influencing hydrogenase expression. Hydrogenase activity was dependent upon a preincubation period in the presence of H
2
under conditions such that the cells did not exhibit nitrogenase activity. H
2
uptake rates were easily measured amperometrically in aerobically or anaerobically prepared suspensions from free-living cultures. Six
R. japonicum
strains that formed nodules with the ability to utilize H
2
oxidized this gas when grown in free-living cultures. In comparison six randomly chosen strains forming nodules that lost H
2
in air either showed no or low capacity to take up H
2
under free-living conditions. The reduction of triphenyltetrazolium chloride in an agar medium was used to detect strains capable of oxidizing H
2
. This method has enabled us to isolate a spontaneous
R. japonicum
mutant strain that has lost the ability to utilize H
2
. This mutant strain forms nodules that evolve H
2
but other symbiotic characteristics appear normal. This strain will be useful in evaluating the importance of the hydrogenase system in the nitrogen-fixing process of legumes.
Subunit molecular weight and genetic variability of proteins in natural populations.
Authors: Nei M , Fuerst P A , Chakraborty R
Published: May 2006

The relationship between subunit molecular weight and heterozygosity was studied in six different groups of organisms, i.e., 9 species of primates, 32 species of rodents, 56 species of reptiles, 12 species of salamanders, 64 species of teleost fishes, and 29 species of Drosophila. The correlation coefficient between them was positive in all groups, and the magnitude of correlation was roughly in agreement with the theoretical expectation under the mutation-drift hypothesis when the incomplete correlation between molecular weight and mutation rate was taken into account. Furthermore, the correlation was higher when the average heterozygosity was high than when this was low, as theoretically expected.
High yield photoreagents for protein crosslinking and affinity labeling
Authors: Jelenc Pierre C. , Cantor Charles R. , Simon Sanford R.
Published: May 2006

4-Nitrophenyl ethers are proposed as new high-yield photoreagents for protein crosslinking and affinity labeling. These are totally unreactive in the dark under biological conditions, but react quantitatively with amines at pH 8 upon irradiation with 366-nm light. The reaction of monoalkoxy-
p
-nitrobenzenes with an amine yields the corresponding free alcohol and substituted nitrophenylamine. In essence, the nitrophenyl group is transferred from the alcohol to the amine. Bifunctional affinity reagents of this type could be especially useful for placing the
p
-nitrophenyl chromophore adjacent to a binding site without blocking it. The corresponding 2-methoxy-4-nitrophenyl ethers react with amines by displacement of the methoxyl group. Thus, bifunctional reagents of this class could be photocrosslinkers. A maleimide-containing 2-methoxy-4-nitrophenyl ether was attached to human fetal hemoglobin at γ-cysteine F9 stoichiometrically. Subsequent ultraviolet irradiation yielded a γ-γ crosslinked hemoglobin in 80% yield. The oxygenation properties of the derivative indicate that it is locked in a high affinity conformation and that all cooperativity is lost.
Compact oligomers and nucleosome phasing.
Authors: Tatchell K , Van Holde K E
Published: May 2006

Micrococcal nuclease (EC 3.1.4.7) digestion of histone H1- and H5-depleted chicken erythrocyte chromatin yields, in addition to 140-base-pair (bp) core particles, a series of nucleosome oligomers containing about 260 bp (compact dimer), 380 bp (compact trimer), etc. of DNA. These are postulated to represent members of a class of oligomers in which the DNA is tightly wound on stacked protein cores. The physical properties (melting, circular dichroism) as well as DNase I (EC 3.1.4.5) digestion patterns support this view. DNase I digestion of tight oligomers in which the 5' ends of the DNA have been labeled yields results consistent with this model and inconsistent with some other possible models. Several classes of such particles are postulated to exist, differing in DNA length by 10-bp increments. This may be an explanation of the 10-bp nucleosome "phasing" that has been observed in some nuclei.
Functional consequences of ligand-dependent conformational changes in trypsin-solubilized and in membrane particle constrained-acetylcholinesterase.
Authors: Pattison S , Bernhard S
Published: May 2006

The effect of a class of ligands on the catalytic activity of acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) from Torpedo californica electroplax tissue has been studied via the transient reaction of a fluorophoric acetylcholine analog, 7-(N,N-dimethyl)carbamoxy-N-methylquinolinium iodide (M7C). These "peripheral" ligands inhibit the formation of a metastable carbamyl-enzyme intermediate from M7C. They induce slow isomerization to a new conformational state that shows little or no reaction with M7C. At saturating ligand concentration, the unimolecular isomerization rate constant is 0.03 +/- 0.01 sec-1, a slow rate compared to the rate of carbamylation of the active conformation. Peripheral ligands alter the distribution between reactive and unreactive conformations, thus inducing biphasic rates and amplitudes of carbamylation. The amplitudes, but not the two specific rates, are affected by the concentration of ligand. Zn2+ and d-tubocurarine are two ligands that induce the same slow isomerization rate. On the basis of this identity of function by ligands of disparate structure, we postulate the existence of only a single active conformation and a single inactive conformation (stabilized by interaction with both ligands). In the absence of ligands, the active conformation predominates. Peripheral ligands bind specifically to the inactive conformation. Alkaline earth cations such as Ca2+ and Mg2+ interact strongly and preferentially with the active conformation and drive the conformational equilibrium toward the active state. Ligand-induced inactivation is observed both with highly purified trypsin-solubilized enzyme and with enzyme bound to unfractionated membrane fragments.
Partial amino acid sequence of penicillinase coded by Escherichia coli plasmid R6K.
Authors: Ambler R P , Scott G K
Published: May 2006

Direct studies of the amino acid sequence of an Escherichia coli plasmid-coded penicillinase (penicillin amido-beta-lactamhydrolase, EC 3.5.2.6) are in complete agreement with results derived from the translation of the DNA sequence of a related plasmid, apart from a single amino acid substitution. This penicillinase from a Gram-negative bacterium shows 30-35% identity with functionally similar enzymes from Gram-positive bacteria. This paper should be read in conjunction with the report of the DNA sequence of the gene.
Sodium-stimulated active transport of aminoisobutyric acid by reconstituted vesicles from partially purified plasma membranes of mouse fibroblasts transformed by simian virus 40.
Authors: Nishino H , Tillotson L G , Schiller R M , Inui K I , Isselbacher K J
Published: May 2006

Plasma membrane fractions isolated from mouse fibroblast BALB/c 3T3 cells transformed by simian virus 40 were partially purified by treatment with dimethylmaleic anhydride followed by extraction with 2% cholate. The extracted proteins were combined with exogenous phospholipids and eluted through a Sephadex G50 column. Reconstituted vesicles thus obtained were shown to possess the ability of Na+-stimulated transport of alpha-aminoisobutyric acid. The simultaneous addition of NaSCN and alpha-aminoisobutyric acid to these vesicles produced a transient accumulation above the equilibrium level (overshoot, active transport). The Na+-stimulated transport of alpha-aminoisobutyric acid was sensitive to the accompanying anion and to the temperature of incubation. The results demonstrate that partially purified membrane proteins of mouse fibroblast cells can be incorporated into the liposomes that have the characteristics of Na+-stimulated and electrochemically sensitive active transport of alpha-aminoisobutyric acid.
Effect of inbreeding on IQ and mental retardation.
Authors: Morton N E
Published: May 2006

Both decline of IQ and increase of mental retardation are consistent with rare recessive alleles at about 325 loci. There is no suggestion of a discrepancy that might be due to polygenic dominance or confounding of consanguinity with unfavorable environment. These data indicate that the risk for mental retardation in matings of normal parents increases from 0.012 with random mating to 0.062 for first-cousin parentage but that dominance deviations are a negligible cause of family resemblance of IQ. Implications for frequencies, mutation rates, and radiation response are detailed.
Mechanisms of trypanosome-mediated suppression of humoral immunity in mice
Authors: Albright Julia W. , Albright Joseph F. , Dusanic Donald G.
Published: May 2006

Spleen cells from
Trypanosoma musculi
-infected mice were unable to respond to sheep erythrocyte antigen
in vitro
; moreover, they suppressed the responses of normal spleen cell cultures in dose-dependent fashion. Suppression was maximal with spleen cells obtained during maximal parasitemia and waned as the donors recovered from infection. A macrophage-enriched population of spleen cells from infected mice, prepared either by adherence to plastic or by density gradient centrifugation, was not contaminated by the parasites and was not suppressive, whereas the plastic-nonadherent population was both contaminated and suppressive. Adherent and nonadherent cells of infected mice, separated by use of nylon wool columns, were almost equally suppressive and equally contaminated by trypanosomes. Addition of specific rabbit antiserum against
T. musculi
to cultures containing cells from infected mice eliminated contaminating parasites and alleviated suppression exerted by cells obtained from mice early during the course of infection but not after 12-15 days of infection. The suppression exerted by enriched T-cells obtained from mice on day 12 of infection was largely alleviated by use of the antiserum. A large portion of cells obtained on day 14 of infection could be killed by the antiserum and complement. It appeared that soluble substances derived from the parasites acted directly on B lymphocytes or essential assistant cells rather than by activating suppressor T cells or macrophages.
Involvement of an interneuron in the generation of the slow inhibitory postsynaptic potential in mammalian sympathetic ganglia.
Authors: Dun N J , Karczmar A G
Published: May 2006

Acetylcholine (AcCho) was applied electrophoretically to cells of isolated rabbit superior cervical ganglia, and the response was recorded by means of intracellular recording techniques. In the presence of d-tubocurarine (5 micron), AcCho applied by tetanic current pulses elicited three distinct membrane potential changes: a slow depolarization, a slow hyperpolarization, and a biphasic response consisting of an initial hyperpolarization followed by a depolarization. Atropine (1 micron) abolished all the membrane potential changes elicited by AcCho. On the other hand, superfusion with a low-Ca/high-Mg solution, tetrodotoxin (0.1 micron), or haloperidol (0.1 micron) selectively and reversibly blocked AcCho-induced hyperpolarization without appreciably affecting the depolarization. The membrane resistance remained relatively constant during the course of hyperpolarization. Application of steady depolarizing and hyperpolarizing currents decreased and increased, respectively, the amplitude of hyperpolarization. These results demonstrate that the hyperpolarization elicited by AcCho is electrophysiologically and pharmacologically similar to the slow inhibitory postsynaptic potential induced by nerve stimulation; furthermore, they support the view that the slow inhibitory postsynaptic potential elicited by presynaptic stimulation is a disynaptic phenomenon involving the release of a second transmitter, possibly dopamine, from an interneuron.
Some implications of an alternative structure for DNA.
Authors: Sasisekharan V , Pattabiraman N , Gupta G
Published: May 2006

We have constructed a space-filling (Corey-Pauling-Koltun) model of an alternative structure for DNA. This structure is not a double helix, but consists of a pair of polynucleotide strands lying side by side and held together by Watson-Crick base pairing. Each of the two strands has alternating right- and left-handed helical segments approximately five base pairs in length. Sugar residues in alternating segments along a strand point in opposite directions. A structure slightly different from the present one proposed earlier by ourselves and another group and in which sugars in a strand all point in the same direction is ruled out. The present structure yields natural solutions to the problems of supercoiling of DNA and of strand separation during DNA replication. This model is energetically more favorable than the double helix.
Hatching in the sea urchin Lytechinus pictus is accompanied by a shift in histone H4 gene activity.
Authors: Grunstein M
Published: May 2006

There is a distinct shift in histone mRNA synthesis at approximately 11--12 hr of sea urchin emhryogenesis, coincident with embryonic hatching. The synthesis of the blastula type (early) histone mRNAs gradually ceases at this stage and a new class of posthatching (late) histone mRNAs is produced. Briefly labeled early and late mRNAs were isolated and identified by means of RNA-DNA hybridization to different cloned histone genes. The late histone HI mRNA is approximately 40 nucleotides longer than the early HI mRNA. The H3, H2A, H2B, and H4 late mRNAs are 15--40 nucleotides shorter than their early counterparts. We present sequence evidence to show that the genes coding for the late H4 mRNA are a separate class from those that code for the early histone H4 message.
6-beta-bromopenicillanic acid, a potent beta-lactamase inhibitor.
Authors: Pratt R F , Loosemore M J
Published: May 2006

6-beta-Bromopenicillanic acid, which arises from the epimerization of 6-alpha-bromopenicillanic acid in aqueous solution or from hydrogenation of 6,6-dibromopenicillanic acid, is a powerful, irreversible, active-site-directed inhibitor of several typical beta-lactamases (penicillinase; penicillin amido-beta-lactamhydrolase, EC 3.5.2.6); 6-alpha-bromopenicillanic acid, being completely inhibited at less than micromolar concentrations through what is probably a 1:1 interaction. The B. licheniformis exoenzyme is similarly susceptible, while the Staphylococcus aureus enzyme and the Escherichia coli (R factor) enzyme are less so; the B. cereus beta-lactamase II is not inhibited. Very high concentrations (greater than or equal to 0.1 M) of benzylpenicillin, a good substrate, are required to significantly reduce the rate of inhibition of B. cereus beta-lactamase I by 6-beta-bromopenicillanic acid.
Mechanism of adenylate cyclase activation through the beta-adrenergic receptor: catecholamine-induced displacement of bound GDP by GTP.
Authors: Cassel D , Selinger Z
Published: May 2006

The fate of the guanyl nucleotide bound to the regulatory site of adenylate cyclase was studied on a preparation of turkey erythrocyte membranes that was incubated with [3H]GTP plus isoproterenol and subsequently washed to remove hormone and free guanyl nucleotide. Further incubation of this preparation in the presence of beta-adrenergic agonists resulted in the release from the membrane of tritiated nucleotide, identified as [3H]GDP. The catecholamine-induced release of [3H]GDP was increased 2 to 3 times in the presence of the unlabeled guanyl nucleotides GTP, guanosine 5'-(beta,gamma-imino)triphosphate [gpp(NH)p], GDP, and GMP, whereas adenine nucleotides had little effect. In the presence of Gpp(NH)p, isoproterenol induced the release of [3H]GDP and the activation of adenylate cyclase, both effects following similar time courses. The findings indicate that the inactive adenylate cyclase possesses tightly bound (GDP, produced by the hydrolysis of GTP at the regulatory site. The hormone stimulates adenylate cyclase activity by inducing an "opening" of the guanyl nucleotide site, resulting in dissociation of the bound GDP and binding of the activating guanosine triphosphate.
Interaction between actomyosin and 8-substituted ATP analogs.
Authors: Takenaka H , Ikehara M , Tonomura Y
Published: May 2006

Various 8-substituted ATP analogs were synthesized, and their reactions with myosin and actomyosin were studied. The nucleoside triphosphates (NTPs) with an amino group at the 6 position and hydrogen at the 8 position, and formycin 5'-triphosphate (FTP) were hydrolyzed by myosin very slowly in the presence of Mg2+ and rapidly in the presence of EDTA and K+. In contrast, NTPs with substitution of the 8 position, other than FTP, were readily hydrolyzed by myosin in the presence of Mg2+ but were hardly hydolyzed in the presence of EDTA and K+. The Michaelis constant (Km) for hydrolysis of 8-substituted NTP by heavy meromyosin was much larger than the dissociation constant (Kfl) for binding of heavy meromyosin with NTP estimated from the change in tryptophan fluorescence. All the NTPs with no substitution at the 8 position, and FTP, caused an initial Pi burst, actin activation of myosin NTPase, superprecipitation of actomyosin, and myofibrillar contraction. On the other hand, all the 8-substituted NTPs in three possible conformations did not cause these phenomena, regardless of the conformation. These results were discussed in relation to the hindrance of rotation about the glycosidic bond accompanying an 8 substitution.
Nucleosome rearrangement in human chromatin during UV-induced DNA- reapir synthesis.
Authors: Smerdon M J , Lieberman M W
Published: May 2006

The distribution of UV-induced DNA repair synthesis within chromatin was measured in confluent human fibroblasts that were pulse-labeled with [3H]dThd (10 or 90 min) immediately after irradiation and chased in nonradioactive medium for different time periods. Initially (i.e., at the end of the pulse period), most of the repair synthesis occurs in staphylococcal nuclease-sensitive regions. With increasing chase times the nucleotides inserted during repair synthesis become progressively more nuclease resistant. Gel electrophoresis data indicate that nuclease resistance is conferred on these nucleotides by their appearance in core DNA. The kinetics of this rearrangement process are biphasic: greater than 85% of the repair synthesis sites undergo rapid rearrangement (4--5 hr); the remaining sites ( less than 15%) rearrange much more slowly, if at all. The time courses of nucleosome rearrangement and repair synthesis are similar, suggesting that nucleosome rearrangement may be induced by the repair process or that the rate of repair synthesis may be regulated by nucleosome rearrangement.
Temperature-sensitive replication of H5ts125 adenovirus DNA in vitro.
Authors: Horwitz M S
Published: May 2006

A soluble adenovirus DNA replication system has been prepared in extracts of HeLa cells infected with the temperature-sensitive mutant H5ts125. These nuclear extracts synthesize full-sized viral DNA at 30 degrees but are temperature sensitive in this function at 38 degrees. A 72,000-dalton DNA-binding protein purified from cells infected with wild-type virus complements the temperature-sensitive defect and restores viral DNA replication to 74% of normal values.
Magnesium reverses inhibitory effects of calcium deprivation on coordinate response of 3T3 cells to serum
Authors: Rubin A. H. , Terasaki M. , Sanui H.
Published: May 2006

Deprivation of Ca
2+
in crowded cultures of 3T3 cells inhibits the onset of DNA synthesis. By raising [Mg
2+
] to 15 mM the inhibition produced by Ca
2+
deprivation can be fully overcome. Sparse cultures are not inhibited by a similar deprivation of Ca
2+
, and therefore are not stimulated by supranormal [Mg
2+
]. The time course of stimulation of the onset of DNA synthesis by supranormal [Mg
2+
] in low [Ca
2+
] is the same as that produced by serum in physiological concentrations of Ca
2+
and Mg
2+
. Concentrations of Mg
2+
> 20 mM in low [Ca
2+
] reverse the stimulation, and [Mg
2+
] ≥ 30 mM kills many cells. In contrast to the stimulation by 15 mM Mg
2+
, supranormal [Ca
2+
] has no effect on the onset of DNA synthesis in cultures inhibited by Mg
2+
deprivation, if the formation of insoluble Ca-P
i
complexes is prevented. Neither Na
+
nor K
+
reproduces the effects of Mg
2+
. The uptake of uridine is another parameter of the coordinate response of 3T3 cells to serum stimulation that is inhibited by Ca
2+
deprivation, and supranormal [Mg
2+
] also reverses this inhibition. The results support the thesis that the coordinate response of growth and metabolism to external effectors is regulated by the availability of Mg
2+
within the cell and that the inhibitory effects of Ca
2+
deprivation are indirect and caused by a reduction in the availability of Mg
2+
.
Attachment and spreading of baby hamster kidney cells to collagen substrata: effects of cold-insoluble globulin.
Authors: Grinnell F , Minter D
Published: May 2006

Studies have been carried out to determine the effects of cold-insoluble globulin (CIG) on the attachment and spreading of baby hamster kidney cells on various collagen substrata. Cell attachment to native collagen substrata occurred in the absence of CIG just as fast as attachment to dried collagen or gelatin substrata occurred in the presence of CIG. On the other hand, cell attachment to dried collagen or gelatin was markedly reduced in the absence of CIG. Cell spreading also occurred on native collagen in the absence of CIG; however, CIG was absolutely required for cell spreading to occur on dried collagen or gelatin. Finally, anti-CIG antiserum or lactoperoxidase treatment inhibited cell spreading on CIG-coated substrata but not on native collagen substrata. The data are discussed in terms of the interaction of fibroblasts with collagen in situ.
Another chromosomal assignment for a simian virus 40 integration site in human cells.
Authors: Kucherlapati R , Hwang S P , Shimizu N , McDougall J K , Botchan M R
Published: May 2006

Somatic cell hybrids derived from fusion of GM637, a human cell line transformed by simian virus 40, and mouse B82 cells were examined for simian virus 40 T antigen, V antigen, and viral DNA. All hybrid cell lines that contained viral DNA were T-antigen positive. Cells that did not have viral DNA were T-antigen negative. We determined that there is a single viral insertion in these hybrid cells. Correlation of T-antigen expression and viral DNA with the partial complements of the human genome retained in the hybrids shwed that the inserted viral genome is in human chromosome 8. The integrated viral DNA is stable; free viral DNA found in GM637 does not insert at other potential sites in the human genome.
Azo dyes prevent hydrocarbon-induced leukemia in the rat.
Authors: Huggins C B , Ueda N , Russo A
Published: May 2006

A set of intraveous injections of 7,8,12-trimethylbenz[a]anthracene consistently elicited leukemia in more than 75% of young adult Long-Evans female rats. There was a profound reduction in the incidence of leukemia in companion groups of rats fed small amounts (1--10 mg) of Sudan III or Sudan IV prior to each injection of the carcinogenic hydrocarbon. Repeated feedings of 1 mg of Sudan III induced cumulative increases in the concentration of menadione reductase (EC 1.6.99.2) in liver, whereas protein concentration was unchanged. A single feeding of 1 mg of Sudan III prevented fatal toxicity in all members of large groups of rats injected with massive doses of 7,12-dimethylbenz[a]anthracene, but 50% of the survivors developed leukemia; unprotected rats succumbed in 1--3 days. Sudan III was not carcinogenic under the experimental conditions.
Benjamin—Ono-related equations and their solutions
Authors: Case K. M.
Published: May 2006

It is shown that the Benjamin—Ono equation is one of a hierarchy of nonlinear partial differential singular integral equations. Explicit multisoliton solutions are constructed for all equations of the hierarchy.
Interaction of wild-type and variant mouse 3T3 cells with lectins from Bandeiraea simplicifolia seeds.
Authors: Stanley W S , Peters B P , Blake D A , Yep D , Chu E H , Goldstein I J
Published: May 2006

An isolectin (BS I-B4) derived from Bandeiraea simplicifolia seeds and specific for terminal alpha-D-galactopyranosyl groups was found to be cytotoxic to Swiss 3T3 mouse cells. After mutagenesis and selection with BS I-B4, a variant clonal cell line resistant to both this isolectin and the alpha-D- and beta-D-galactose-binding lectin abrin was isolated. The parental cell line showed homogeneous and noninteracting binding sites for BS I-B4, whereas the variant cells exhibited a curved plot with a reduced number of binding regions. Another lectin, BS II, which is derived from the same seeds by specific for terminal N-acetyl-D-glucosaminyl groups, was cytotoxic to the variant but not the parental cells. These results suggest a possible lesion in the biosynthesis of cell surface structures resulting in the exposure of subterminal N-acetyl-D-glucosaminyl moieties in the variant line.
An oligosaccharide-containing factor that induces cell differentiation in Dictyostelium discoideum.
Authors: Town C , Stanford E
Published: May 2006

When Dictyostelium discoideum amoebae (strain V12 M2) are spread at high density on agar containing 1 mM cyclic AMP, essentially all the cells differentiate into stalk cells after 2-3 days. We showed previously that isolated amoebae plated at low density on agar containing cyclic AMP do not differentiate, but can be induced to do so by a layer of high density helper cells from which they are separated by a thin cellophane membrane. We now show that the high density cell population releases a dialyzable factor that, in the presence of cyclic AMP, is capable of inducing isolated amoebae to differentiate into stalk cells. Sugar inhibition, sensitivity to glycosidases, and lectin affinity suggest that the differentiation-inducing activity requires the integrity of an oligosaccharide group containing sialic acid, L-fucose, and N-acetylgalactosamine. In addition, a phosphate group appears to be necessary for biological activity.
Unstable spiral modes in disk-shaped galaxies: A general fluid dynamical theory with some preliminary results
Authors: Pannatoni R. F. , Lau Y. Y.
Published: May 2006

A numerical scheme has been devised to calculate discrete spiral modes in a fluid-dynamical model of disk galaxies. The procedure is free from the usual restrictions imposed upon the asymptotic theory. A radiation condition has been formulated as one of the boundary conditions. For a test model galaxy with moderately low surface density, quantitative agreement is found between the asymptotic spiral modes and the corresponding ones obtained from the present scheme. The present scheme should find ready application to the study of open spiral modes.
Emetine resistance in Chinese hamster cells is linked genetically with an altered 40S ribosomal subunit protein, S20.
Authors: Boersma D , McGill S M , Mollenkamp J W , Roufa D J
Published: May 2006

Emr-2 is an emetine-resistant (Emr) Chinese hamster ovary cell mutant that contains a single electrophoretically altered ribosomal protein, a component of its 40S ribosomal subunit [Boersma, D., McGill, S., Mollenkamp, J. & Roufa, D.J. (1979) J. Biol. Chem. 254, in press]. This report describes a genetic experiment designed to test linkage between the genes that specify the altered ribosomal protein, S20*, and emetine resistance in Emr clones that segregated from cultures of Emr-2 cells hybridized with emetine-sensitive cells. The data described indicate that Emr and S20* phenotypes are due to mutations linked to the same chromosome in the Chinese hamster genome; most likely they are due to the same mutation. The data also confirm earlier speculations by others that the Emr locus in Chinese hamster cells is hemizygous.
Dynamics of density- and frequency-dependent selection
Authors: Nagylaki Thomas
Published: May 2006

The evolution of a multiallelic locus in a diploid monoecious population is investigated for weak selection in both discrete and continuous time. It is assumed that in the absence of selection the rate of change of population size
N
is a function only of
N
, and
N
converges exponentially to a unique, globally stable equilibrium,
^N
. With arbitrary density- and frequency-dependent selection, after several generations have elapsed,
N
differs from
^N
by terms of
O(s)
(i.e., bounded by a constant times
s
), where
s
is the selection intensity. The mean absolute fitness deviates from its equilibrium value (1 in discrete, 0 in continuous time) by only
O
(
s
2
); its rate of change is
O
(
s
3
). The evolution of the gene frequencies may be approximated with an error of
O
(
s
) by assuming that
N
=
^N
and Hardy-Weinberg proportions obtain. When the frequency dependence is weaker than the selection intensity, the mean absolute fitness generally exceeds its equilibrium value by a quantity approximately proportional to the genic variance, the constant of proportionality being simply related to the rate of convergence of
N
to
^N
in the absence of selection. Thus, after a short time, the population generally increases, and the rate of growth is proportional to the genic variance.
Impairment of cell-mediated immunity functions by dietary zinc deficiency in mice
Authors: Fernandes Gabriel , Nair Madhavan , Onoe Kazunori , Tanaka Toshio , Floyd Rachael , Good Robert A.
Published: May 2006

Several immunologic features were analyzed in mice on a zinc-deficient diet [Zn(-)], in mice pair-fed a diet containing zinc [Zn(+)], in mice fed a Zn(+) diet ad lib, and in mice fed laboratory chow ad lib. When placed on a Zn(-) diet, 6- to 8-week-old A/Jax, C57BL/Ks, and CBA/H mice showed loss of body weight, low lymphoid tissue weight, and profound involution of the thymus within 4-8 weeks after initiation of the regimen. Approximately 50% of the mice on the Zn(-) diet developed severe acrodermatitis enteropathica (lesions on tail and paws) and diarrhea. Pair-fed mice on the Zn(+) diet did not show any of these symptoms. Mice on the Zn(-) diet showed the following immune deficiencies: (
i
) depressed plaque-forming cells against sheep erythrocytes after
in vivo
immunization; (
ii
) depressed T killer cell activity against EL-4 tumor cells after
in vivo
immunization; and (
iii
) low natural killer cell activity. However, antibody-dependent cell-mediated cytotoxicity against chicken erythrocytes was normal in the mice on the Zn(-) diet. Deficiency of T killer cell activity was not observed when immunization with EL-4 allogeneic lymphoma cells was carried out
in vitro
. Progressive loss of relative and absolute number of Thy 1.2+ cells and a proportionate relative increase in cells bearing Fc receptors was seen in spleen and lymph nodes of Zn(-) animals. It appears that zinc is an essential element for maintenance of normal T cell and other immune functions
in vivo
.