bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectral-Kinetic Heterogeneity in Reactions of Nitrosyl Hemoglobin
Authors: Salhany J. M. , Ogawa S. , Shulman R. G.
Published: May 2006

When NO replaces CO in hemoglobin A in the presence of inositol hexaphosphate, the time course is heterogeneous in contrast to stripped hemoglobin A, where it is homogeneous. If nitrosyl hemoglobin is mixed with inositol hexaphosphate in the stopped-flow apparatus, an extra spectral change is observed which is the cause of the spectral-kinetic heterogeneity in the CO replacement reaction. At wavelengths isosbestic for this extra spectral change, the time courses show an accelerating rate of CO dissociation. On the other hand, the same reaction for NES-des-Arg hemoglobin (hemoglobin reacted with
N
-ethylmaleimide and carboxypeptidase B) in the presence of inositol hexaphosphate is homogeneous and slow, and shows isosbesty. High-resolution nuclear magnetic resonance spectra indicate that adult nitrosyl hemoglobin in the presence of inositol hexaphosphate is in the low ligand affinity state, thus offering a structural basis for the acceleration observed in the rate of CO dissociation. Hemoglobin Kansas, in the presence of inositol hexaphosphate, which starts and finishes the reaction in the low affinity state, shows a rate of CO dissociation about nine times faster than stripped hemoglobin A. We conclude from these results that (
i
) the CO to NO replacement reaction can include a functionally important change in the overall conformation of fully liganded hemoglobin, depending on solution conditions and protein type; (
ii
) the extra spectral change observed for nitrosyl hemoglobin is not the functionally dominating conformational change, but is a secondary effect within the low ligand affinity protein structure; and (
iii
) the functional properties of heme ligands are largely controlled by two conformational states of the protein, as seen by nuclear magnetic resonance spectroscopy.
The Wavelengths in Sunlight Effective in Producing Skin Cancer: A Theoretical Analysis
Authors: Setlow R. B.
Published: May 2006

DNA is taken as the target for skin cancer induced by ultraviolet light, and the known data on the sensitivity of DNA as a function of wavelength are summarized. The sun's spectrum at the surface of the earth and the DNA action spectrum are used to calculate the carcinogenic effectiveness as a function of wavelength. The most effective wavelengths at 30°N latitude are <305 nm, and a 1% change in atmospheric ozone results in a 2% change in the effective dose of ultraviolet light. Since both the basic biological and physical data are reasonably precise, the major requirement for a quantitative evaluation of the dose response relation for ultraviolet-induced skin cancer in man is better epidemiological data to compare with data from animal models.
The 7S RNA Common to Oncornaviruses and Normal Cells is Associated with Polyribosomes
Authors: Walker T. A. , Pace N. R. , Erikson R. L. , Erikson E. , Behr F.
Published: May 2006

The 7S RNA species first demonstrated in avian and murine oncornaviruses and later in normal, uninfected cells is found associated in part with cellular polyribosomes. A molar ratio of 7S RNA to 5S ribosomal RNA of 0.05 indicates that there is approximately one mole of 7S RNA per mole of messenger RNA. Dissociation of polyribosomes with dimethylsulfoxide results in a marked decrease in the sedimentation rate of the 7S RNA. The dimethylsulfoxide-induced dissociation of polyribosomes and the concomitant movement of the 7S RNA from the polyribosome region into lighter regions of a sucrose gradient are both inhibited by cycloheximide, indicating that the 7S RNA is indeed associated with polyribosomes and not with a ribonucleoprotein particle sedimenting with polyribosomes.
Plasmid ColE1 as a Molecular Vehicle for Cloning and Amplification of DNA
Authors: Hershfield Vickers , Boyer Herbert W. , Yanofsky Charles , Lovett Michael A. , Helinski Donald R.
Published: May 2006

DNA fragments obtained from
Eco
RI endonuclease digestion of bacteriophage ϕ80pt190 (
trp
+
) and the plasmid ColE1 were covalently joined with polynucleotide ligase. Transformation of
Escherichia coli trp
-
strains to tryptophan independence with the recombined DNA selected for reconstituted ColE1 plasmids containing the tryptophan operon and the ϕ80 immunity region. Similarly, an
Eco
RI endonuclease generated fragment of plasmid pSC105 DNA containing the genetic determinant of kanamycin resistance was inserted into the ColE1 plasmid and recovered in
E. coli
. The plasmids containing the
trp
operon (ColE1-
trp
) and the kanamycin resistance gene were maintained under logarithmic growth conditions at a level of 25-30 copies per cell and accumulate to the extent of several hundred copies per cell in the presence of chloramphenicol. Cells carrying the ColE1-
trp
plasmid determined the production of highly elevated levels of
trp
operon-specific mRNA and tryptophan biosynthetic enzymes.
Distribution and Fate of Synthetic Lipid Vesicles in the Mouse: A Combined Radionuclide and Spin Label Study
Authors: McDougall I. R. , Dunnick June K. , McNamee M. G. , Kriss J. P.
Published: May 2006

Single compartmental spherules of various lipid constituents (vesicles), enclosing

99
m

TcO
4
-
as a radioactive marker, were injected intravenously into C
3
H mice, and the distribution of radioactivity was studied. About 25% of the administered radioactivity was present in the liver 5 min and 30 min after the injection of vesicles composed of phosphatidylcholine and gangliosides, which were sonicated for 5 min (standard preparation). About 10-20% of the radioactivity remained in the circulation. By use of a nonradioactive spin label (tempocholine) enclosed within vesicles, intact vesicles were demonstrated in the circulation for 46 min after intravenous injection. The distribution of radioactivity from

99
m

TcO
4
-
inside vesicles is very different from that of free

99
m

TcO
4
-
or of

99
m

Tc sulfur colloid.

Increase in the length of sonication or incorporation of cholesterol into the wall of the vesicles enhanced hepatic levels and reduced blood levels of radioactivity. These same manipulations also slowed the rate of transfer of

99
m

TcO
4
-
out of vesicles in dialysis experiments
in vitro
. Addition of phosphatidic acid, phosphatidylethanolamine, or phosphatidylserine to the standard constituents did not greatly alter the distribution of radioactivity
in vivo
but did increase the number and type of active coupling sites on the outside of the vesicle. The results indicate that vesicles might be valuable as carriers of diagnostic or therapeutic agents.
Cellular Immunity Against Rous Sarcomas of Chickens. Preferential Reactivity Against Autochthonous Target Cells as Determined by Lymphocyte Adherence and Cytotoxicity Tests
In Vitro
Authors: Wainberg M. A. , Markson Y. , Weiss D. W. , Doljanski F.
Published: May 2006

Spleen cells from random-bred chickens bearing Rous sarcomas were commonly more reactive against the neoplastic target cells in autochthonous than in allogenic interactions
in vitro
. This difference was observed both in cytotoxic assays (
51
Cr release from labeled target cells) and in an immunoadherence test measuring attachment of
51
Cr-labeled splenocytes to Rous sarcoma cells. Specific splenocyte reactivity was not observed with normal embryonic chicken fibroblasts, 3T3 cells, or embryonic mouse C3H fibroblasts. The immunoadherence technique required only 2 hr to perform, and revealed a more consistent superiority of autochthonous recognition of Rous sarcoma cells than the cytotoxicity assay. Experiments in which both procedures were used simultaneously with identical cell populations yielded similar results, indicating that splenocyte adherence may be a precursor of and/or concomitant to target cell damage and that individual-specific tumor antigencity may play a part in cellular immunity against Rous sarcomas.
The Primary Structure of High Density Apolipoprotein-Glutamine-I
Authors: Baker H. Nordean , Delahunty Thomas , Gotto Antonio M. , Jackson Richard L.
Published: May 2006

The major protein constituent of human plasma high density lipoproteins has been isolated and its complete amino-acid sequence determined. The protein, designated apolipoprotein-glutamine-I by the presence of carboxyl-terminal glutamine, is a single polypeptide chain of 245 amino-acid residues, including three residues of methionine. The protein is devoid of cysteine, cystine, and isoleucine. Cleavage of apolipoprotein-glutamine-I with cyanogen bromide yields four fragments with 94, 90, 36, and 25 amino acids. The amino-acid sequence of each fragment was determined by conventional methods, with proteolytic digestion with trypsin, chymotrypsin, and thermolysin. The alignment of the cyanogen bromide fragments was determined by the isolation of the methionine-containing tryptic peptides from apolipoprotein-glutamine-I.

Inspection of the sequence of apolipoprotein-glutamine-I suggests an interesting distribution of amino acids that may account for its helical structure and its ability to bind and transport lipid.
Molecular Basis for the Photosynthetic Primary Process
Authors: Fong Francis K.
Published: May 2006

In this paper, the molecular details for the primary reaction in photosynthesis are deduced from several recent critical experimental observations. A symmetrical structure is proposed for the basic unit of the reaction center in plant photosynthesis. A mathematical consequence of the symmetrical arrangement is the creation of an anomalously long-lived trap state, which makes possible the summation of a reaction-center triplet excitation and an antenna chlorophyll singlet excitation to bring the photoactive chlorophylls to a charge-transfer state prior to entering into a primary photochemical reaction.
Covalent Joining of Phenylalanine Transfer Ribonucleic Acid Half-Molecules by T4 RNA Ligase
Authors: Kaufmann Gabriel , Littauer Uriel Z.
Published: May 2006

RNA ligase from T4-phage-infected
Escherichia coli
cells catalyzes the covalent joining of two polynucleotides that are partially hydrogen-bonded to each other. Two polynucleotide fragments derived from yeast tRNA
Phe
and consisting of residues 1-36 and 38-74 are covalently joined by the enzyme. The product of the reaction lacks residue Y
37
and has an anticodon loop with six nucleotide residues, whereas all tRNA species whose sequences have so far been determined have seven nucleotides in this loop.

Evidence is also presented for the formation of a polynucleotide-adenylylate intermediate in the joining reaction, in which a pyrophosphate bond links the 5′-phosphoryl terminus of the polynucleotide and the phosphoryl group of AMP.
Regulation of the Fatty Acid Composition of the Membrane Phospholipids of
Escherichia coli
Authors: Cronan John E.
Published: May 2006

An increase in the dosage of the
fabA
gene, which codes for the enzyme β-hydroxydecanoyl thioesterase, causes an increase in the unsaturated fatty acyl content of the phospholipids. This increase is small in cells growing at a constant temperature. However, if cells grown at 37 or 42° are shifted to 15°, the rate of unsaturated fatty acyl moiety synthesis approaches twice the rate of a normal strain. These results indicate that the ratio of unsaturated to saturated fatty acyl groups in phospholipids is partially determined by the levels of at least this fatty acid biosynthetic enzyme.
T4-induced RNA ligase joins single-stranded oligoribonucleotides.
Authors: Walker G C , Uhlenbeck O C , Bedows E , Gumport R I
Published: May 2006

RNA ligase isolated from Escherichia coli infected with bacteriophage T4 will catalyze the formation of an intermolecular 3' leads to 5' phosphodiester linkage between an oligoribonucleotide with a free 3'-hydroxyl and another oligoribonucleotide with a 5'-phosphate. Upon reaction with (Ap)5C, nearly quantitative conversion of the hexamer [5'-32P]p(Up)5U to the dodecamer (Ap)5C[3' leads to 5'-32P]p(Up)5U was observed. The product was identified by its mobility on RPC-5 column chromatography, its resistance to alkaline phosphatase, and the appearance of the expected radiolabeled products on hydrolysis with alkali, ribonuclease A, snake venom phosphodiesterase, and spleen phosphodiesterase. The coupling of other pairs of single-stranded oligoribonucleotides has also been demonstrated. The intermolecular joining reaction is probably mechanistically similar to the intramolecular cyclization activity previously reported for Tr RNA ligase. It is expected that this enzyme will be useful for the synthesis of RNA fragments of defined sequence.
Calcium role in depolarization-secretion coupling: an aequorin study in squid giant synapse.
Authors: Llinás R , Nicholson C
Published: May 2006

Aequorin, a protein that emits light in the presence of calcium, was injected in the presynaptic terminal of the squid giant synapse. This injection was preceded by intracellular tetraethylammonium administration, which prolonged the duration of the presynaptic action potential. After this procedure light emission was evoked by single presynaptic spikes capable of releasing synaptic transmitter. In a second set of experiments, presynaptic tetraethylammonium injection was followed by the administration of tetrodotoxin extracellularly, which abolished the presynaptic action potential. Under these conditions artificial depolarization of the presynaptic terminal triggered the release of synaptic transmitter, in a graded manner. However, as previously reported by other authors, membrane potential steps to an internal positive value of approximately plus 90 mV (the suppression potential) produced a blockage of transmitter release for the duration of the imposed potential. Synaptic transmission recurred, nevertheless, as the current injection was terminated. A similar set of experiments, performed after the intracellular injection of aequorin in the presynaptic fiber, demonstrated that the aequorin light response was evoked by membrane potential steps capable of releasing synaptic transmitter. If the membrane potential was made positive to the "suppression" level, no light response was evoked but the light emission appeared, as did transmitter release, at the end of the current pulse. These experiments demonstrate that release of transmitter is directly correlated with intracellular calcium concentration and that the suppression potential is compatible with the existence of a calcium equilibrium potential at the presynaptic terminal.
Sequential Estimation of
p
with Squared Relative Error Loss
Authors: Cabilio Paul , Robbins Herbert
Published: May 2006

We consider the sequential estimation of
p
, the probability of success in an infinite sequence of Bernoulli trials, when the loss incurred in stopping after
n
trials and estimating
p
by some function δ

n

of the first
n
outcomes is taken to be [Formula: see text] The loss due to error of estimation is thus the symmetrized
relative
squared error, which is appropriate in applications when
p
may be near 0 or 1.

We begin by finding a heuristic procedure for sequentially determining the sample size
n
which, with the usual terminal estimator of
p
, performs well for any fixed 0 <
p
< 1 as the cost per observation
c
→ 0. For any fixed
c
> 0, however, this procedure is poor as
p
→ 0 or 1. To remedy this defect, the uniform prior on
p
is introduced. The corresponding Bayes procedure is found and is shown to have a Bayes risk ∼2π√
c
as
c
→ 0.
Inhibition of oncornavirus functions by 2'-azido polynucleotides.
Authors: De Clercq E , Billiau A , Hobbs J , Torrence P F , Witkop B
Published: May 2006

The 2'-azido analogs of poly(U) and poly(C), poly(dUz) [poly(2'-azido-2'-deoxyuridylic acid)], and poly-(dCz [poly(2'-azido-2'-deoxycytidylic acid)], were found to inhibit the RNA-directed DNA polymerase (reverse transcriptase) activity of murine leukemia (Moloney, Rauscher) and sarcoma (Moloney) virus, and feline leukemia (Theilen) and sarcoma (Gardner) virus, while under the same conditions the unsubstituted parent compounds failed to do so. In addition, poly(dUz) and poly(dCz) inhibited the replication of exogenous murine sarcoma virus (Moloney) in nontransformed cells (as assessed by an infectious center assay), but poly(dUz) failed to suppress the formation of endogenous sarcoma and leukemia viruses in transformed cell lines (MO-P, JLSV5). In these same cells, poly(dUz) failed to inhibit the multiplication of vesicular stomatitis virus. These data add further strength to the contention that reverse transcriptase is necessary for the productive infection and transformation of normal cells by oncornaviruses but is not essential maintenance of this transformed state and the continuous production of new viruses particles by these transformed cells.
Correlated suppression by 5-bromodeoxyuridine of tumorigenicity and plasminogen activator in mouse melanoma cells.
Authors: Christman J K , Silagi S , Newcomb E W , Silverstein S C , Acs G
Published: May 2006

The decrease of tumorigenicity by mouse melanoma clone B559 after growth in the presence of 5-bromodeoxyuridine (BrdU) has been correlated with a decrease in detectable cellular plasminogen activator. Reduction of both activities occurs after one to two cell divisions in the presence of this thymidine analog and is virtually complete within three to four cell cycles. These changes are fully reversible; four to five cell divisions in the absence of BrdU are sufficient to allow both tumorigenicity and plasminogen activator levels to return to normal. These results support the hypotheses that (a) the expression of a cellular plasminogen activator is closely associated with the transformation of normal to malignant cells and that (b) the suppression of tumorigenicity by BrdU reflects the capacity of this base analog to inhibit the expression of specialized functions which accompany the malignant state.
Enhancement of soybean RNA polymerase I by auxin.
Authors: Guilfoyle T J , Lin C Y , Chen Y M , Nagao R T , Key J L
Published: May 2006

When etiolated soybean seedlings are treated with the synthetic auxin, 2,4-dichlorophenoxy-acetic acid, cells of the mature hypocotyl become swollen and proliferate abnormally. This abnormal growth induced by auxin coincides with a 5- to 8-fold increase in the alpha-amanitin-insensitive RNA polymerase associated with isolated chromatin or nuclei. The alpha-amanitin-sensitive RNA polymerase activity of the auxin-treated hypocotyl was similar to that of control tissue. The increase in RNA polymerase I activity of chromatin and nuclei was maintained after solubilization and fractionation on DEAE-cellulose. Auxin thus appears to enhance RNA synthetic activity (i.e., ribosomal RNA) in mature soybean tissue by altering RNA polymerase I directly rather than by altering RNA polymerase I directly rather than by altering the chromatin template.
Studies on the primary structure of the influenza virus hemagglutinin.
Authors: Skehel J J , Waterfield M D
Published: May 2006

The amino-terminal sequence and composition of the subunits of the hemagglutinin (HA) of influenza virus has been determined. The hemagglutinin has been isolated by two techniques. (1) as the intact hemagglutinin after disruption of the virus in sodium dodecyl sulfate, giving 2 subunits of 58,000 daltons (HA1) and 26,000 daltons (HA2), and (2) after treatment of the virus with bromelain, giving 2 subunits of 58,000 daltons (BHA1) and 21,000 daltons (BHA2). In both preparations these subunits are linked by disulfide bonds. The aminoterminal sequences of HA1 and BHA1, and HA2 and BHA2 are the same. The composition of the 50 residue peptide associated with the membrane, which is removed from the C-terminus of HA2 by bromelain, is deduced and shown to be hydrophobic and contain 50% of the serine residues of HA2. The biosynthetic precursor of the hemagglutinin has been purified from the membranes of abortively infected chick fibroblasts and shown to have the same amino terminus as HA1. Thus the order of biosynthesis is NH2-HA1-HA2-COOH. The amino-terminal sequence of BHA2--at the cleavage site of the precursor--is shown to be a palindrome: NH2-Gly-Leu-Phe-Gly-Ala-Ile-Ala-Gly-Phe-Ile-. This sequence is conserved in representative viruses from each of the major pandemics. A region of homologous sequence is described between the hemagglutinins of influenza type A and B viruses.
Colony hybridization: a method for the isolation of cloned DNAs that contain a specific gene.
Authors: Grunstein M , Hogness D S
Published: May 2006

A method has been developed whereby a very large number of colonies of Escherichia coli carrying different hybrid plasmids can be rapidly screened to determine which hybrid plasmids contain a specified DNA sequence or genes. The colonies to be screened are formed on nitrocellulose filters, and, after a reference set of these colonies has been prepared by replica plating, are lysed and their DNA is denatured and fixed to the filter in situ. The resulting DNA-prints of the colonies are then hybridized to a radioactive RNA that defines the sequence or gene of interest, and the result of this hybridization is assayed by autoradiography. Colonies whose DNA-prints exhibit hybridization can then be picked from the reference plate. We have used this method to isolate clones of ColE1 hybrid plasmids that contain Drosophila melanogaster genes for 18 and 28S rRNAs. In principle, the method can be used to isolate any gene whose base sequence is represented in an available RNA.
Membrane particles on fracture faces of frozen myelin.
Authors: da Silva P P , Miller R G
Published: May 2006

Freeze-fracture electron microscopy reveals constant and widespread presence of membrane particles on the fracture faces of frozen myelin. In unfixed myelin frozen shortly after dissection the distribution of the particles is uniform. In glutaraldehyde-fixed and/or glycerol-impregnated myelin the particles frequently occupy a network interspersed with circumscribed particle-free areas of variable dimension. In these membranes the network of particles is propagated radially across many lamellae. Particle-rich areas are closely apposed and contrast with frequent delamination of adjacent particle-free regions. We propose that, as in other plasma membranes, the particles of myelin represent protein-containing structures intercalated across the hydrophobic matrix of a membrane with bilayer organization. Our results indicate that these structures contain sites which mutually interact at the surface of apposed membranes and may be important in maintaining the organizational integrity of myelin.
Antibody nature of circulating inhibitor of plasma von Willebrand factor.
Authors: Stratton R D , Wagner R H , Webster W P , Brinkhous K M
Published: May 2006

A circulating plasma inhibitor of the "von Willebrand factor" was observed in a multiply tranfused subject with severe von Willebrand's disease. The platelet-active von Willebrand factor is associated with a plasma protein macromolecular complex that is deficient in the disease. The inhibitor appears to be an IgG antibody, kappa type, based on neutralization tests with goat antisera to specific human immunoglobulins. The IgG and inhibitor separated out together in plasma fractions obtained by "salting-out" and chromatographic procedures. Two separate inhibitor neutralization tests for the platelet-active factor, one with human plasma and ristocetin, the other with bovine plasma, gave similar results, based on the macroscopic aggregation time test of fixed human platelets. With cryoprecipitate transfusions the inhibitor was transiently neutralized with the temporary appearance of von Willebrand factor, factor VIII, and factor VIII-like antigen in the plasma. The plasma inhibitor level increased after transfusion, suggesting an anamnestic response. Lower titer inhibitor plasmas neutralized only the platelet activity. Highest titer plasma also neutralized human factor VIII, but only in part; it did not neutralize either bovine factor VIII or the human small active factor VIII fragment. The anti-factor VIII activity of the von Willebrand factor inhibitor may be due to steric hindrance, dependent on the spatial relationship of factor VIII sites on the macromolecular complex.
Neurohypophyseal hormones, analogs, and fragments: their effect on puromycin-induced amnesia.
Authors: Walter R , Hoffman P L , Flexner J B , Flexner L B
Published: May 2006

Neurohypophyseal hormones and several of their analogs, as well as N-terminal and C-terminal fragments, have been studied for their ability to attenuate puromycin-induced amnesia in mice. [8-Lysine]vasopressin, [8-arginine]vasopressin, and the analogs des-9-glycinamide-[8-lysine]vasopressin, [1-beta-mercaptopropionic acid, 8-lysine]vasopressin, [1,6-aminosuberic acid, 8-lysine]vasopressin, [4-leucine, 8-lysine]vasopressin, glycyl-glycyl-glycyl-[8-lysine]vasopressin, [1-beta-mercaptopropionic acid, 8-D-arginine]vasopressin, and [1,6-aminosuberic acid, 8-arginine]vasopressin are active. [8-Arginine]oxytocin as well as oxytocin and all of its other analogs tested are inactive with the striking exception of glycyl-glycyl-glycyl-oxytocin. The structural aspects of the neurohypophyseal hormones which appear to be important for significant activity in memory consolidation include the combination of a cyclic moiety containing the Tyr and Phe residues along with a basic residue in position 8. Another series of active compounds comprises C-terminal neurohypophyseal peptides and analogs thereof, including the naturally occurring Pro-Leu-Gly-NH2 and, most surprisingly, Leu-Gly-NH2, as well as its derivatives D-Leu-Gly-NH2 and the diketopiperazine, cyclo(-Leu-Gly-).
Raman resonance of electron donor/acceptor complex.
Authors: Michaelian K H , Rieckhoff K E , Voigt E M
Published: May 2006

The resonance Raman excitation profiles of a number of charge transfer transitions in electron donor/acceptor complexes with tetracyanoethylene as acceptor in solution at room temperature are reported and compared with absorption and fluorescence spectra of these complexes. All complexes show distinct anomalies which cannot be accounted for by existing theories unless they are extended. In particular, the excitation profiles peak at the low energy side of the absorption profiles by amounts of the order of 1000-2000 cm-1 and also, in the cases where two charge transfer bands are present, resonance occurs independently for the two bands. The latter observation suggests that the two bands are due to distinct species of the complex with differing geometrical configurations. The former observations is interpreted, in connection with the known asymmetry of the absorption profile and the large Stokes gap between absorption and fluorescence peaks, as arising from the relatively stronger contributions of the pure electronic and vibronic levels in the Stokes gap to the Raman scattering cross-section of the complex, and a frequency dependent damping of the vibronic transitions contributing to resonance. This provides important physical insights into the nature of charge transfer transitions of electron donor/acceptor complexes in general. In our discussion we also refer to similar anomalies in the work of others on the resonance Raman effect of the iodine visible absorption band in solution.
Identification of NADPH-thioredoxin reductase system in Euglena gracillis.
Authors: Munavalli S , Parker D V , Hamilton F D
Published: May 2006

Euglena gracilis contains a protein system which can utilize the reducing power of NADPH in the ribonucleotide reductase-catalyzed reduction of CTP. The proteins required for this reaction are a flavoprotien with a molecular weight of approximately 185,000 which is functionally similar to thioredoxin reductase (NADPH), EC 1.6.4.5, and another protein (Protein I) whose function in the reaction is unknown. This new protein does not appear to contain a prosthetic group and has a molecular weight of approximately 240,000. In addition, the ribonucleotide reductase active in the Euglena NADPH-thioredoxin reductase system is more complex than the protein reported in a previous publication [(1974) j. Biol. Chem. 249, 4428-4434]. The enzyme preparation described in this report contains four different types of polypeptide chains which may complex to form the active enzyme.
Action of nicking-closing enzyme on supercoiled and nonsupercoiled closed circular DNA: formation of a Boltzmann distribution of topological isomers.
Authors: Pulleyblank D E , Shure M , Tang D , Vinograd J , Vosberg H P
Published: May 2006

Highly purified nicking-closing enzyme from mouse cells in 20-fold enzyme/substrate excess converts closed circular native PM2, ColE1, and Minicol DNA into limit product sets of DNAs. Each set has a mean degree of supercoiling of approximately zero. The individual species in the sets differ by deltatau = +/-1, +/-2, etc., and the relative masses fit a Boltzmann distribution. It was also demonstrated that "nonsupercoiled" closed circular duplex molecules serve as substrates for the nicking-closing enzyme, and that a distribution of topological isomers is generated. Polynucleotide ligase, acting on nicked circular DNA, forms under the same conditions, the same set of closed DNAs. The latter enzyme freezes the population into sets of molecules otherwise in configurational equilibrium in solution.
Activation of T and B lymphocytes in vitro: presence of beta2-microblobulin determinants on allogeneic effect factor.
Authors: Armerding D , Kubo R T , Grey H M , Katz D H
Published: May 2006

The biologically acitve entity termed allogeneic effect factor, which is produced by alloantigen-activated T cells and has been shown to regulate triggering and differentiation of B lymphocytes in vitro, has previously been demonstrated to possess antigenic determinants coded by genes in the I region of the H-2 gene complex of the mouse. The studies presented here provide evidence that allogeneic effect factor also possesses antigenic determinants identical or cross-reactive with beta2-microglobulin. These observations suggest an important role for beta2-microglobulin in the mechanism of cell-cell interactions and the consequences of such interactions on lymphocyte triggering and differentiation.
Evolution of human longevity and the genetic complexity governing aging rate.
Authors: Cutler R G
Published: May 2006

Genetic complexity of processes governing the aging rate of man was estimated by determining the maximum rate lifespan has evolved along the hominid ancestral-descendant sequence. Maximum lifespan potential was found to have increased approximately 2-fold over the past 3 million years, reaching a maximum rate of increase of 14 years per 100,000 years about 100,000 years ago. It is estimated that about 0.6% of the total functional genes have received substitutions leading to one or more adaptive amino acid changes during this 100,000-year time-period. This suggests that aging is not the result of an expression of a large number of independently acting processes. Instead, primary aging processes appear to exist where only a few genetic changes are necessary to decrease uniformly the aging rate of many different physiological functions.
Trophic radiation through polymorphism in cichlid fishes
Authors: Sage Richard D. , Selander Robert K.
Published: May 2006

Several morphologically defined species of cichlid fishes (
Cichlasoma
) endemic to the Cuatro Cienegas basin of Mexico and differing in tooth structure, body shape, and diet are allelically identical at 27 gene loci. The presence of only one Mendelian population in each of three drainage systems studied and the occurrence of two of the morphotypes in the same broods indicate that the supposed species are morphs. That trophic radiation in the Cuatro Cienegas cichlids has been achieved through ecological polymorphism rather than speciation raises questions regarding the genetic basis for the extensive intralacustrine radiation of cichlids in Africa and elsewhere.
Nonprevalence of biochemical fossils in kerogen from pre-Phanerozoic sediments
Authors: Leventhal Joel , Suess Stephen E. , Cloud Preston
Published: May 2006

Evidence of biochemical and geochemical evolution was sought in insoluble carbonaceous matter from 30 selected pre-Phanerozoic sediments ranging in age from about 3.8 to about 0.7 × 10
9
years. The carbon isotope ratios observed were in the range of -20 to -32 per mil with reference to the Peedee belemnite standard, similar to those previously reported. No systematic trends are obvious to us. Stepwise pyrolysis-gas-chromatography showed only molecules with fewer than 8 carbon atoms at the level of sensitivity of 10
-9
g of organics in a 10 mg rock sample. Carbon, hydrogen, and nitrogen analyses showed noncarbonate carbon from less than 0.1% to more than 3%, with very small amounts of N. The H/C (atomic) ratios on HCl-leached and HF-treated samples were generally less than 0.3. Evidence of low pyrolysis yields (micro-analysis) and low H/C atomic ratios (macro-analysis) implies that the carbonaceous solids in even the least metamorphosed of these ancient sediments have evolved far toward amorphous carbon or graphite and do not yield useful “biochemical fossils.”
Cellular levels of feedback regulator of adenylate cyclase and the effect of epinephrine and insulin.
Authors: Ho R j , Russell T R , Asakawa T , Sutherland E W
Published: May 2006

We have obtained direct evidence that shows the cellular formation and subsequent release of a potent inhibitor (feedback regulator) of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] by adipocytes, upon stimulation with epinephrine. The appearance of such a feedback regulator in adipocytes preceded its release into the medium. During a 30 min incubation, intracellular regulator levels rose rapidly and reached 39-61 units/g of adipocyte at 10 min. Release of inhibitor into the medium increased slowly and was 11-16 units/g of adipocyte at 10 min. Upon continued incubation, the cells at 30 min contained 30-41 units/g of ingibitor, slightly less than the content at 30 min; meanwhile, the medium content rose more than 3-fold. The inhibitor from both locations appeared to have the same characteristics, judging from the purification procedures and the biological activities on hormone-stimulated adenylate cyclase. Adenylate cyclase was inhibited by the feedback regulator in vitro when either epinephrine, corticotropin (ACTH), or glucagon was used as activator. The site of action of this inhibitor is therefore most likely beyond the specific hormone receptors. A new in vitro action of insulin has been found. Insulin, 50-500 microunits/ml, inhibited the formation and release of this factor from isolated rat or hamster adipocytes by 29-81% after these cells were stimulated by hormones that raise intracellular adenosine 3':5'-cyclic monophosphate. This factor enhaced the effect of insulin in lowering the adenosine 3':5'-cyclic monophosphate levels in fresh rat adipocytes. A reduced formation of such a factor may modify the metabolic events in adipocytes, and some as yet unexplained effects of insulin could therefore be linked to the metabolic effects of this factor.
Chemically induced dynamic electron polarization in chloroplasts at room temperature: evidence for triplet state participation in photosynthesis.
Authors: Blankenship R , McGuire A , Sauer K
Published: May 2006

A transient electron paramagnetic resonance emission is observed after flash excitation of chloroplasts at room temperature. The spectrum of the emission signal is centered at g = 2.0037 and has a linewidth deltaHpp = 4G (4 X 10(-4) tesla). Inhibitor studies and chemical oxidation indicate that the signal is associated with Photosystem I, but the spectrum and kinetics indicate that it is neither P700 nor an iron-sulfur protein. The emission signal rises with the 2-musec time response of the instrument, and decays during the actinic flash. The emission signal is produced on only the first of a pair of strong flashes separated by 100 musec, indicating that the precursor has not been regenerated in that time. The results are discussed with reference to the two currently accepted mechanisms for chemically induced dynamic electron polarization: the radical pair and the photochemical triplet. For several reasons the photochemical triplet mechanism is the more attractive of the two. It is suggested that at room temperature the primary photochemistry of photosystem I proceeds via a triplet state of chlorophyll, and that the species giving rise to the emission signal is the primary electron acceptor of Photosystem I.
13C-nuclear magnetic resonance study of [85% 13C-enriched proline]thyrotropin releasing factor: 13C-13C vicinal coupling constants and conformation of the proline residue.
Authors: Haar W , Fermandjian S , Vicar J , Blaha K , Fromageot P
Published: May 2006

To understand fully interactions between peptides and cellular receptors, peptide side chain conformation must be defined. In many cases the complexity of proton nuclear magnetic resonance (NMR) prevents this but the present work demonstrates this problem can be solved by using 13C enrichment. Selective 13C enrichment of a natural peptide hormone has been achieved by preparing [85% 13C-enriched proline]thyrotropin releasing factor which was examined by 13C NMR spectroscopy at various pH values. Because of the 13C enrichment, one-bonded and three-bonded (vicinal) 13C-13C coupling constants have been determined. The latter vary from 0 to 5 Hz and show bond angle dependence. These data indicate that in this hormone the pyrrolidine ring is not free but fixed in the Cgamma-endo puckered conformation. It has also been possible to assign chemical shift values for a second order 13C NMR spectrum.
Reversal of UDP-galactose 4-epimerase deficiency of human leukocytes in culture.
Authors: Mitchell B , Haigis E , Steinmann B , Gitzelmann R
Published: May 2006

Stimulation with phytohemagglutinin of the leukocytes from six of the seven known individuals with UDP-galactose 4-epimerase (= UDP-glucose 4-epimerase; EC 5.1.3.2) deficiency consistently resulted in the appearance of epimerase activity in the cultured cells. A long-term lymphoblast culture derived from one proband also contained an active epimerase enzyme. A comparison of the properties of this enzyme with those of epimerase produced by control lymphoblast lines revealed comparable Km values for UDP-galactose and NAD and identical behavior on polyacrylamide electrophoresis. However, a difference in the NAD requirement for heat stability at 40 degree provided some evidence for a structural defect in this enzyme. Possible explanations for the appearance of UDP-galactose 4-epimerase activity in stimulated lymphocytes include an increased rate of synthesis of a mutant enzyme and a derepression of an epimerase locus during lymphocyte transformation.
Different responses of lymphoid cells from tumor-bearing as compared to tumor-immunized mice when sensitized to tumor specific antigens in vitro.
Authors: Kall M A , Hellström I , Hellström K E
Published: May 2006

Lymphoid cells from spleen and lymph nodes of BALB/c mice were sensitized in vitro by cocultivation with cells from syngeneic methylcholanthrene-induced sarcomas. The donor mice were either immunized in vivo by tumor transplantation followed by excision ("tumor-excised mice") or were carrying a progressively growing tumor ("tumor-bearing mice"). The cell-mediated immune response of the sensitized cells was compared by a 36-hr microcytotoxicity assay. Lymphoid cells from tumor-excised mice were cytotoxic when tested after 3 days and also after 6 days of sensitization in vitro. Lymphoid cells from tumor-bearing mice were cytotoxic to cells of the tumor borne when tested after 3 days in culture. However, the cytotoxic effect was lost after 6 days of contact with the sensitizing tumor in vitro. Preliminary data suggest that the cultured lymphoid cells of tumor-bearing mice which have lost cytotoxicity, can suppress the reactivity of in vitro sensitized lymphoid cells from tumor-excised mice.
Cyclic nucleotide metabolism coupled to cytodifferentiation of Blastocladiella emersonii.
Authors: Silverman P M , Epstein P M
Published: May 2006

Cyclic GMP and cyclic AMP levels during growth and differentiation of B. emersonii were measured by use of chemical, biochemical, and immunologic assays. Of particular interest was the finding that net synthesis of cyclic GMP occurred during a single stage of its life cycle, sporulation, when intracellular levels increased 50- to 100-fold in a process requiring protein and RNA synthesis.
Simian virus 40-related antigens in three human meningiomas with defined chromosome loss.
Authors: Weiss A F , Portmann R , Fischer H , Simon J , Zang K D
Published: May 2006

Two out of seven meningiomas tested in early cell cultures by indirect immunofluorescence staining showed simian virus 40 (SV40)-related tumor (T) antigen. In one tumor 90% of the cells were positive. An additional SV40-related antigen (U) was found in 10% of cells of a third tumor. These findings indicate that the meningioma cells showing a positive reaction are transformed by a papova virus that has at least partly the same antigenic properties as SV40 virus. SV40-related viral capsid (V) antigen was absent in all the meningiomas tested. No virus infectious for African green monkey kidney (AGMK) cells could be isolated. The tumors positive for T and U antigens showed the chromosome aberration typical for human meningiomas, i.e., the loss of one chromosome, G-22. The T-antigen-positive tumors showed further hypodiploidization. Experiments to rescue virus from the T-antigen-positive tumors showed further hypodiploidization. Experiments to rescue virus from the T-antigen-positive meningioma cells were performed: fusion of cells pretreated with 8-azaguanine with cells premissive for SV40 led to a low percentage (0.01-0.05%) of V-antigen-positive nuclei in heterokaryon cultures. On the basis of these results, the possibility of a correlation between the meningioma, a relatively common intracranial tumor in man, and an SV40-related papova virus must be considered. It remains to be shown whether this virus is a causative agent for human meningiomas.
Induction by RNA of inositol independence in Neurospora crassa.
Authors: Mishra N C , Niu M C , Tatum E L
Published: May 2006

The effect of purified wild-type RNA (allo-RNA) on genetic reversion of inositol-requiring mutant 89601 of Neurospora crassa is described. The mutant (inos minus) strain, on treatment with the wild-type RNA preparation, was found to revert to wild type (inos+) in significant numbers. RNA from the mutant (iso-RNA) and allo-RNA digested by RNase were ineffective in causing genetic reversion at the inositol locus. The allo-RNA-induced revertants were stable and showed a Mendelian transmission of the inos+ character.
A theory of evolution above the species level.
Authors: Stanley S M
Published: May 2006

Gradual evolutionary change by natural selection operates so slowly within established species that it cannot account for the major features of evolution. Evolutionary change tends to be concentrated within speciation events. The direction of transpecific evolution is determined by the process of species selection, which is analogous to natural selection but acts upon species within higher taxa rather than upon individuals within populations. Species selection operates on variation provided by the largely random process of speciation and favors species that speciate at high rates or survive for long periods and therefore tend to leave many daughter species. Rates of speciation can be estimated for living taxa by means of the equation for exponential increase, and are clearly higher for mammals than for bivalve mollusks.
Spectator-ion effect on the passage of ions through membranes.
Authors: Kozak J J
Published: May 2006

In this paper, we investigate the interplay between geometric and dielectric factors in influencing the image force acting on an ion passing through a membrane, for a system having the approximate dimensions of Escherichia coli. We also study the effect of one ion in a membrane on the passage of a second ion through the membrane, by calculating the radial and angular forces experienced by the second ion due to the presence of the "spectator ion." Our conclusions follow from numerical studies on expressions obtained by solving (exactly) Laplace's equation for the model assumed in this paper. The conclusions are: (i) small changes in the dielectric constant of the membrane are far more significant in determining the image force acting on an ion in a membrane than dramatic changes in the dielectric character of the regions interior and/or exterior to the cell; (ii) a spectator ion in a membrane situated near a boundary may influence in a significant way the passage of a second ion through the middle third of the membrane. We suggest that this latter result should be taken into account in discussing the mechanism of ion migration across membranes.
Non-specific stimulation of cell-free protein synthesis by a dialyzable factor isolated from reticulocyte initiation factors ("iRNA").
Authors: Berns A , Salden M , Bogdanovsky D , Raymondjean M , Schapira G , Bloemendal H
Published: May 2006

The specificity of a dialyzable component, isolated from rabbit reticulocyte initiation factors, in stimulating protein synthesis was examined. It appeard that his factor (hereafter designated as "iRNA") was able to restore the activity of initiation factor preparations that were inactivated by dialysis. The "iRNA" from reticulocytes stimulated polypeptide synthesis directed by the homologous globin mRNA as well as heterologous lens crystallin mRNAs. No selectivity in its stimulating action with regard to the type of mRNA studied could be observed. The source of ribosomes or supernatant enzymes did not influence the effect of "iRNA". However, in an ascites lysate that was dependent on the addition of initiation factors, "iRNA" increased polypeptide formation only marginally, suggesting that in this lysate a similar factor was already present in an active form. It is concluded that "iRNA" may regulate protein synthesis, but without exhibiting specificity towards mRNAs, at least those tested so far.
Control of the mRNA for hepatic tryptophan oxygenase during hormonal and substrate induction.
Authors: Schutz G , Killewich L , Chen G , Feigelson P
Published: May 2006

Glucocorticoid hormones increase the level of hepatic tryptophan oxygenase (EC 1.13.11.11; L-tryptophan:oxygen 2,3-oxidoreductase (decyclizing) by increasing its rate of synthesis. Studies were performed to determine whether this induction is mediated by controlling the level of the mRNA for tryptophan oxygenase of by changing the translational efficiency of a fixed level of mRNA. Activity of tryptophan oxygenase mRNA was quantitated in a Krebs ascites cell-free, protein-synthesizing system, supplemented with tRNA and rabbit reticulocyte initiation factors. De novo synthesis of the protomeric unit(s) of the enzyme was a linear function of the amount of mRNA added. Time course and dose-response studies in which the enzyme level and mRNA activity in livers from rats injected with inducing doses of hydrocortisone were compared indicate that the induction of this enzyme is accompanied by a proportional increase in the level of its mRNA. This was true for mRNA isolated from total liver as well as from cytoplasmic polysomes. Induction of the enzyme by its substrate, tryptophan, however, was not accompanied by a parallel increase in mRNA activity.
Crystallization of nerve growth factor from mouse submaxillary glands.
Authors: Wlodawer A , Hodgson K O , Shooter E M
Published: May 2006

Crystals of the nerve growth factor protein were grown by vapor diffusion from ethanol solution. The crystals are hexagonal, belonging to space group P622 (or its enantiomorph) with a equals 56.1 A, c equals 181.4 A, and V equals 494,400 A. The unit cell contains six molecules of dimeric protein and thus has one monomer per asymmetric unit. The diffraction pattern extends to at least 2.7 A, indicating that this crystal form is suitable for structural analysis to near-atomic resolution.