bluuebunny/crossref_metadata_2025 huggingface dataset:
Cooperative Interactions in Aspartate Transcarbamoylase. 1. Hybrids Composed of Native and Chemically Inactivated Catalytic Polypeptide Chains
Authors: Gibbons Ian , Yang Ying R. , Schachman H. K.
Published: May 2006

Hybrids of aspartate transcarbamoylase (EC 2.1.3.2; carbamoylphosphate: L-aspartate carbamoyltransferase) from
Escherichia coli
containing native (active) and pyridoxylated (inactive) catalytic polypeptide chains were constructed by a procedure involving the reversible acylation of amino groups with 3,4,5,6-tetrahydrophthalic anhydride. This technique exploited the charges contributed by the tetrahydrophthaloyl groups as a “chromatographic handle” for separating the various species. Enzyme-like molecules containing one fully active and one inactive catalytic subunit showed cooperative kinetic behavior, considerable inhibition by CTP, and a substantially increased apparent

K
m

compared to the native enzyme. Similar properties were observed for an intrasubunit hybrid containing one inactive catalytic polypeptide chain in each subunit. The cooperative inter-and intra-subunit hybrids also exhibited conformational changes similar to those found for the native enzyme upon the addition of stereospecific ligands. These observations, taken together with data for other complexes of catalytic and regulatory subunits, illustrate the importance of the architecture of aspartate transcarbamoylase and the quaternary constraint stemming from the subunit interactions.
Parametric Analysis of Conductance Data
Authors: Fuoss Raymond M.
Published: May 2006

It is shown that three and only three parameters are sufficient to generate a function Λ (
c;
Λ
0
,
K
A
,
R
) which reproduces observed equivalent conductance Λ as a function of concentration
c
within experimental error up to concentrations of about 2 × 10
-7
D
3
eq/liter (
D
= dielectric constant). The three parameters are: Λ
0
, the limit of Λ(
c
) at zero concentration;
K
A
, the association constant; and
R
, a distance. Realization that conductance data can provide only one distance parameter suggests a model for electrolytic solutions in which
R
is defined as the radius of the sphere inside of which a unique partner can be found for a paired ion, and outside of which continuum theory may be applied. All system-specific effects (ion-ion and ion-solvent interactions, and the inherent spatial discontinuity of real solutions) appear within the spheres of radius
R
centered at the cations of the ion pairs. The association constant therefore depends not only on electrostatic attraction but also on the multiplicity of molecular parameters that are needed to describe short range interactions.
Evolution of Type C Viral Genes: I. Nucleic Acid from Baboon Type C Virus as a Measure of Divergence among Primate Species
Authors: Benveniste Raoul E. , Todaro George J.
Published: May 2006

Hybridization studies with a [
3
H]DNA probe from an endogenous baboon type C virus were used to detect nucleic acid sequences of type C virus in primate cellular DNA. Sequences related to those of the baboon type C virus are found in all other Old World monkey species, higher apes, and man.
A Statistical Study of Optical Rotation for Synthetic D,L-Copolypeptide Solutions
Authors: Gotoh Haruo , Lin S. H. , Eyring H.
Published: May 2006

The right-handed helical fraction H
L
in a D,L-copolypeptide chain is evaluated by a simple probability theory for each L-fraction,
p
. The curves of optical rotation at a single wavelength against
p
for poly(γ-benzyl-D,L-glutamate) and D,L-copolyleucine of a series of different D:L ratios in several positive helix-solvents are calculated with a modified semi-empirical Moffitt equation. From the comparison between the rotations calculated by us and observed by Downie
et al
., it is shown that to reproduce the observed rotations, the minimum number of right-handed helical nuclei or sequences of L-residues appropriate to the Moffitt equation are eight and four for degrees of polymerization 320 and 1860, respectively.
The Three-Dimensional Organization of the Amplified Ribosomal DNA Complex in
Acheta
Authors: Lima-De-Faria A.
Published: May 2006

The major chromomere of pachytene chromosome 6 in the oocytes of
Acheta
(Orthoptera) is a region of amplification for ribosomal RNA cistrons (28 S and 18 S). This chromomere was isolated and studied with the scanning electron microscope. It has an outer shell that is smooth at early stages but divides into polygonal plates as indentations appear on its surface. These indentations increase in number as the DNA copies separate from each other and as the ribosomal RNA synthesis progresses. The vertices of the polygonal plates coincide with the positions at which the DNA copies reach the surface of the chromomere during their “puffing” process. The combined information gained from scanning and transmission electron microscopy, DNA measurements, DNA·RNA hybridization, and cytochemistry, leads to a three-dimensional picture of the organization of the amplified ribosomal DNA in its association with ribosomal RNA and protein.
The Stars of Low Luminosity
Authors: Luyten Willem J.
Published: May 2006

A search has been made among the faint stars with large proper motion found on the Palomar Survey plates for objects that, statistically—judging from their magnitude, color, and proper motion—would appear to be fainter than one ten-thousandth of the sun's luminosity. A total of 122 such objects have been found, and an analysis made for solar motion among them does, indeed, indicate that they must be of exceedingly low luminosity.
Endonuclease Activity Associated with Purified PM
2
Bacteriophages
Authors: Laval Françoise
Published: May 2006

An endonucleolytic activity is associated with purified PM
2
bacteriophages. It converts the double-stranded supercoiled PM
2
DNA mostly into the linear form that sediments as a homogenous peak in alkaline sucrose gradients. The same activity is found in intact or detergent-lysed phages. Optimal activity is observed between pH 6.8 and 7.5 at 28°. Divalent cations, Mg
2+
or Mn
2+
, are necessary for activity, and the enzyme is inhibited by RNA. The endonuclease has no appreciable activity on linear DNA molecules, but it attacks single-stranded circular DNA.
Deoxysubstitution in RNA by RNA Polymerase
In Vitro:
A New Approach to Nucleotide Sequence Determinations
Authors: Paddock Gary V. , Heindell Howard C. , Salser Winston
Published: May 2006

Deoxynucleotides have been incorporated into RNA synthesized
in vitro
by RNA polymerase with either double-stranded or single-stranded DNA as a template. By use of this technique to block or promote cleavage at a particular phosphodiester bond, a variety of specific cleavages may be obtained with the available ribonucleases and deoxyribonuclease I. These methods should greatly increase the ease and rapidity of nucleotide sequence determinations.
Conversion of Protein Nitrogen into Gaseous Catabolites by the Chick Embryo
Authors: Costa Giovanni , Kerins Mary E. , Kantor Ferenc , Griffith Kenneth , Cummings Walter B.
Published: May 2006

Chicken eggs incubated under hatchery conditions for 19 days show significant decreases in the total content of water and organic nitrogen, but not of sodium or potassium. The hypothesis is discussed that the formation of gaseous nitrogen is responsible for the nitrogen loss.
The Kinetics of Conformational Changes in Hemoglobin, Studied by Laser Photolysis
Authors: Alpert B. , Banerjee R. , Lindqvist L.
Published: May 2006

Photolysis of carbon monoxide and oxygen derivatives of hemoglobin by a short laser pulse produces a transient species that rapidly decays to normal deoxyhemoglobin. The effect, which is also observed on single chain proteins and on noncooperative aggregated forms, has been interpreted as corresponding to structural changes in the heme pocket on ligand dissociation. The decay of the transient species follows first-order kinetics with constants ranging from 0.8 to 1.8 × 10
7
sec
-1
. In cooperative hemoglobins, the kinetic constants are pH-dependent, though remaining first- or pseudo first-order at all wavelengths. This shows the close linkage of tertiary and quaternary structure changes in normal hemoglobin.
Replication of the Resident Repressed Epstein-Barr Virus Genome During the Early S Phase (S-1 Period) of Nonproducer Raji Cells
Authors: Hampar Berge , Tanaka Akiko , Nonoyama Meihan , Derge Jeffery G.
Published: May 2006

Replication of the resident repressed Epstein-Barr virus genome in synchronized nonproducer Raji cells was shown to occur during the early S phase (S-1 period) by hybridization of cell DNA with virus-specific complementary RNA (cRNA). The S-1 period was previously identified as the critical period for virus activation induced by thymidine analogues. The findings reported here and elsewhere are consistent with the proposal that: (
i
) virus activation is initiated at or near the site of association of the resident viral genome with cell DNA, (
ii
) replication of the resident virus genome in nonactivated cells is under cell control mechanisms, and (
iii
) the resident virus genome is physically associated with early replicating cell DNA.
Lipid-Protein Interactions in High Density Lipoproteins
Authors: Assmann Gerd , Brewer H. Bryan
Published: May 2006

Delipidated high density lipoprotein (apo-HDL), isolated apolipoproteins apoA-I and apoA-II,
S
-carboxymethylated apoA-II, apoC-III, the NH
2
- and COOH-terminal CNBr peptides of apoA-II, and the COOH-terminal CNBr peptide of apoA-I were recombined
in vitro
with [
N-C
3
H
3
-
choline
]phosphatidylcholine (PC) and [
N
-
14
CH
3
-
choline
]sphingomyelin (SPM). The lipid-protein complexes were analyzed by ultracentrifugal flotation, agarose gel chromatography and circular dichroism. ApoHDL, apoA-II, and
S
-carboxymethylated apoA-II readily recombined with PC or SPM to form particles that were similar in size to native HDL. The COOH- but not the NH
2
-terminal CNBr peptide of apoA-II recombined with lipid. ApoA-I and the COOH-terminal CNBr peptide of apoA-I, however, recombined with PC or SPM to only a limited extent, suggesting that protein-protein interactions between apoA-I and apoA-II are important in the integration of apoA-I into recombined lipoprotein particles. Analysis of the recombined lipid-protein complexes by circular dichroism indicated that there was an increase in helical structure concomitant with lipid-protein binding. The reconstituted particles had many of the physical and chemical properties of the native lipoprotein.
Synthesis of DNA in Human Lymphocytes: Possible Control Mechanism
Authors: Fridlender Bertold R. , Medrano Estela , Mordoh José
Published: May 2006

Partially purified, isolated nuclei from lymphocytes either stimulated or not stimulated by phytohemagglutinin can equally well synthesize DNA when [
3
H]dTTP is used as precursor. Studies of DNA polymerase activity in nuclei and cytoplasm from these cells showed that the enzyme can be detected in either stimulated or nonstimulated lymphocytes. In nonstimulated lymphocytes the uptake of thymidine is very low. The use of inhibitors such as cycloheximide, arbinosylcytosine, and actinomycin D showed that a parallel existed between thymidine uptake and DNA synthesis. All the conditions in which DNA synthesis was inhibited resulted also in an inhibition of thymidine uptake.
Light-Dependent Redistribution of Ions in Suspensions of Chloroplast Thylakoid Membranes
Authors: Hind Geoffrey , Nakatani Herbert Y. , Izawa Seikichi
Published: May 2006

Ion movements associated with the pH rise that is observed upon illumination of thylakoid suspensions at low pH have been studied by a multiparameter technique. Light-dependent, dark-reversible fluxes of H
+
, Cl
-
, Na
+
, K
+
and divalent cations were monitored, together with simultaneous changes in the optical density of the suspension. Extensive uptake of Cl
-
and efflux of Mg
2+
accompany the apparent inward movement of H
+
in the light. Only minor efflux of K
+
is seen and Na
+
appears immobile. The Cl
-
and Mg
2+
fluxes together compensate for most of the charge transferred as H
+
, contributing respectively about 49% and 43% on an equivalent basis. The ratio of Cl
-
influx to Mg
2+
efflux is variable, but usually >1.0. The Mg
2+
flux can be supplanted by (
1
) K
+
flux, if the K
+
/Mg
2+
activity ratio in the suspension is high, and (
2
) Ca
2+
flux, if the thylakoids are equilibrated with suspending media containing Ca
2+
. The affinity of the divalentcation-binding sites, or carrier mechanism, is greater for Ca
2+
than for Mg
2+
. Schemes can be drawn up to account for the observed ion movements on the basis of either a chemical or a chemiosmotic mechanism for energy transduction in chloroplasts. In intact chloroplasts, light-dependent control of Mg
2+
distribution between thylakoid and stroma could serve to regulate enzyme activities in the carbon fixation pathway, and hence photosynthesis.
Contraction Transients of Skinned Muscle Fibers
Authors: Podolsky R. J. , Gulati J. , Nolan A. C.
Published: May 2006

The contraction kinetics of calcium-activated skinned muscle fibers were studied after step decreases in load by means of a quickly responding recording system. The steady velocity at a given relative load was close to that found in electrically stimulated, intact muscle fibers. The presteady motion had the same shape as that of intact fibers, but the time scale of the transient was nearly two times slower. The duration of the initial phase of the motion, where the velocity was greater than the steady value, and the time at which the subsequent low velocity phase ended, were both stretched out to the same extent. Changing the temperature had the same effect on the length of these two phases of the transient. The results indicate that both phases of the transient are produced by the same underlying factors and can be taken as evidence that the entire transient originates in the crossbridge mechanism. In this case the experimental technique described here provides a basis for distinguishing between chemical parameters that affect contractility by (
a
) controlling the number of sites at which crossbridges can be formed, as opposed to (
b
) changing the kinetic properties of a given number of sites.
The Role of the Thymus in a Genetically Controlled Defect of the Immune Response at the Carrier Level
Authors: Mozes Edna , Sela Michael
Published: May 2006

The genetic control of the immune response may be either specific for antigenic carrier or for determinant. We describe here results which show that a carrier-dependent strain defect in immune response is reflected in thymocytes. These results are in agreement with our hypothesis that the genetic defect in the immune response is reflected in thymocytes when the poor response is at the carrier level, whereas it is expressed in the bone marrow population when the low responsiveness is strictly at the determinant level. SWR mice are low responders to multichain polyproline. Furthermore, this mouse strain does not produce antibodies to determinants such as peptides of phenylalanine and glutamic acid (Phe,Glu) or to the loop peptide of lysozyme when attached to polyproline, although they respond well to the same antigenic determinants when conjugated to multichain poly(DL-alanine). Transfer experiments in which irradiated SWR recipients were injected with excess of DBA/1 thymocytes (which do not exhibit a defect in response to polyproline) mixed with graded numbers of SWR marrow cells, prior to immunization with poly(Tyr,Glu)-poly(Pro)--poly(Lys), have indicated that the poor response potential of SWR mice to polyproline is not reflected in their bone marrow cells. Allogeneic transfers in which mixtures of thymocytes and marrow cells from high and low responders were injected into irradiated mice, followed by immunization with poly(Tyr,Glu)-poly(Pro)--poly(Lys) or poly(Phe,Glu)-poly(Pro)--poly(Lys) have demonstrated a clear defect in the thymus derived population of SWR mice when the response potential to polyproline and to determinants attached to it was tested.
Population Structure in Relation to Cost of Selection
Authors: Grant Verne , Flake Robert H.
Published: May 2006

The opposing requirements in an evolving population for a rapid rate of multiple gene substitution and for the maintenance of normal population size can be reconciled in a variety of ways. The ways out of the impasse suggested here invoke deviations from the usual assumption of a large continuous population with constant numbers. In a colonial population system there may be significant random fluctuations in the accidental mortality rate between different colonies; and those colonies with reduced numbers of accidental deaths could tolerate the larger number of selective deaths that go hand in hand with rapid evolution. In new daughter colonies founded by one or a few colonizing individuals from a large polymorphic ancestral population, some genes may reach complete fixation in one or a few generations, without the usual concomitant selective cost. Or, in the same setup, the favored alleles may change by chance from rare to moderately common, but not to complete fixation, during the founding of some daughter colonies; and this raises the allele frequencies above the low range, where the cost of selection is greatest, so that the cost of further selective changes is bearable.
The Quaternary Structure of δ-Aminolevulinic Acid Dehydratase from Bovine Liver
Authors: Wu Wen H. , Shemin David , Richards Kenneth E. , Williams Robley C.
Published: May 2006

The quaternary structure of δ-aminolevulinic acid dehydratase (5-aminolaevulinate hydrolyase, EC 4.2.1.24) from bovine liver was examined by analytical ultracentrifugation, polyacrylamide gel electrophoresis, and electron microscopy. The molecular weights, determined by sedimentation-velocity and sedimentation-equilibrium experiments, were 289,000 and 282,000, respectively. The molecular weight of the subunit in 6 M guanidine. HCl was 34,900 as determined by sedimentation-equilibrium and 35,000 as estimated by polyacrylamide gel electrophoresis. No evidence was obtained for the presence of a smaller polypeptide. It appears therefore that δ-aminolevulinic acid dehydratase from liver is composed of eight subunits. The molecules of the enzyme deposited in thin layers of negative stain were generally square with an edge length of 85-90 Å. On the assumption that the subunits are spherical in shape with a diameter of 44 Å and a density of 1.36 g/cm
3
, the molecular weight of the octamer is calculated to be 292,000. The particles appear to consist of four discrete lobes arrayed at the four corners of a square. The above conclusion that the dehydratase possesses eight subunits can be readily reconciled with the appearance of the enzyme in the electron microscope if it is postulated that the eight subunits are arranged at the corners of a cube. Therefore, it would follow that the subunits are arranged with dihedral (D
4
) symmetry.
The Enzymatic Release of
O
6
-methylguanine and 3-methyladenine from DNA Reacted with the Carcinogen
N
-methyl-
N
-nitrosourea
Authors: Kirtikar D. M. , Goldthwait D. A.
Published: May 2006

Endonuclease II (deoxyribonucleate oligonucleotidohydrolase, EC 3.1.4.30) of
Escherichia coli
has been shown to break phosphodiester bonds in alkylated DNA and depurinated DNA. The hypothesis that depurination is a step in the mechanism of the reaction with alkylated DNA is supported by
in vitro
experiments with DNA reacted with
N
-methyl-
N
-nitrosourea. Endonuclease II releases
O
6
-methylguanine and 3-methyladenine, but not 7-methylguanine, from DNA that has been methylated by the carcinogen
N
-methyl-
N
-nitrosourea.
The Polypeptide Composition of Intra-axonally Transported Proteins: Evidence for Four Transport Velocities
Authors: Willard Mark , Cowan W. Maxwell , Vagelos P. Roy
Published: May 2006

Using a method of gradient gel electrophoresis coupled with autoradiography, we have analyzed the polypeptide composition of the proteins being transported down the axons of the projecting neurons of the rabbit retina. This analysis reveals: (
1
) the molecular weight distribution of 43 transported polypeptides; (
2
) the existence of at least four components of intra-axonal protein transport, each characterized by an unique polypeptide composition as well as by an unique velocity of transport; (
3
) the disappearance of individual labeled intra-axonally transported proteins from the axons and synaptic terminals with half-times ranging from several hours to more than 8 days.

The possibility that intra-axonal transport functions as a temporal mediator of alterations in axonal or synaptic events is discussed in relation to these findings.
The Psychological Concept of “Losing Move” in a Game of Perfect Information
Authors: Simon Herbert A.
Published: May 2006

From a game-theoretic standpoint, in any two-person game of perfect information, each position is won, lost, or drawn, and a move is to be considered an error only when it transfers the game from a more favorable to a less favorable state. A psychological concept of error is quite different, in that it must take into account the fallibility of the players as information processing systems. This paper introduces a psychological concept of error in such games based on the distinction between “obvious” and “problematic” moves, and proposes a formalism for this concept that appears to capture, at least to a first approximation, the notion of “losing move” as that phrase is actually used by players in games like chess.
The Derivation of Ecological Relationships from Physical and Chemical Principles
Authors: Morowitz Harold J.
Published: May 2006

Organic reaction networks are formalized by representing chemical species as points in a space and representing reactions by connectivity rules. Using the generalized network, the behavior of the system is investigated under conditions of electronically exciting input and output to a thermal reservoir. Under steady-state conditions the system undergoes material cycles of the type shown by the major ecological cycles. A consideration of the attractor nature of the equilibrium state of the system leads to the conclusion that the energetically lowest-lying molecules must be inputs into the material cycles. Certain general features of the ecological system are thus shown to follow from the physical and chemical properties of an organic reaction network.
On Some Isospectral Second Order Differential Operators
Authors: Kac Mark , Moerbeke Pierre Van
Published: May 2006

A method of exhibiting potentials which are uniquely determined by their spectra is discussed and illustrated in an example.
Induction of a Lactogenic Receptor in Rat Liver: Influence of Estrogen and the Pituitary
Authors: Posner Barry I. , Kelly Paul A. , Friesen Henry G.
Published: May 2006

A receptor exists in female rat liver with high specificity for lactogenic hormones. Previous work showed the receptor level increased at the time of puberty in female but not male animals. Pregnancy caused a further substantial increase. Here we show that estrone (50 μg/day) administration to male rats induced a 10- to 30-fold increase in specific binding of ovine prolactin and human growth hormone after 8-12 days with a significant increase first seen after 4 but not 2 days of injection. In females, this regimen increased binding to pregnancy levels. In prepuberal (20-days-old) male and female rats, estrone was also markedly stimulatory. The binding sites for ovine prolactin and human growth hormone were of high affinity in liver membranes from both female and estrone-treated male rats (
K
a
= 0.6 to 1.4 × 10
9
M
-1
).

Estrone and estradiol were equally effective in inducing the lactogenic receptor. Estriol (50 μg/day), progesterone (500 μg/day), human placental lactogen (1 mg/day), and testosterone (100 μg/day) were without influence. Hypophysectomy drastically decreased the levels of lactogenic receptor in mature female rats, and estrogen treatment failed to restore receptor levels to normal. Hypophysectomized male rats were also unresponsive to estrogen. Throughout these studies the specific binding of
125
I-labeled insulin remained relatively constant.

This work demonstrates estrogen induction of a lactogenic receptor. The pituitary gland appears to have a critical, though presently undefined, role in the induction process.
Enhancement of DNA Synthesis in a Mammalian Cell-Free System by Trypsin Treatment
Authors: Brown Ronald L. , Stubblefield Elton
Published: May 2006

DNA synthesis in a broken cellular preparation of Chinese hamster cells was enhanced approximately 10-fold by a brief trypsin treatment. Alphachymotrypsin also enhanced the synthesis, whereas Pronase did not. The trypsin appears to be acting on a component of the nucleus. Evidence suggests that the trypsin is not removing protein from the DNA, but may be activating the system some other way.
13
C High-Resolution Nuclear Magnetic Resonance Studies of Enzyme-Substrate Reactions at Equilibrium. Substrate Strain Studies of Chymotrypsin-
N
-Acetyltyrosine Semicarbazide Complexes
Authors: Robillard George , Shaw Elliott , Shulman R. G.
Published: May 2006

N
-Acetyl-L-tyrosine semicarbazide is hydrolyzed by chymotrypsin (EC 3.4.21.1) to
N
-acetyl-L-tyrosine and semicarbazide. If a high concentration of semicarbazide is present, the equilibrium for the reaction can be shifted from hydrolysis to synthesis. Using
N
-acetyl-L-[
13
C]tyrosine enriched at the carboxyl carbon and high concentrations of semicarbazide hydrochloride, we have studied the enzyme-substrate complex of
N
-acetyl-L-[
13
C]tyrosine semicarbazide and chymotrypsin A
δ
by
13
C nuclear magnetic resonance. We observe no shift within the experimental accuracy of ±0.05 ppm as the fraction of substrate bound is changed from 0.17 to 0.70. Since E + S ⇄ ES is in fast exchange on the nuclear magnetic resonance time scale, it is possible to show that when the substrate is bound to the enzyme in the Michaelis complex, the
13
C resonance is shifted less than 0.1 ppm, indicating that negligible substrate strain occurs in this complex at the site of enzymatic attack. These experiments demonstrate the application of nuclear magnetic resonance to the study of particular states along the reaction pathway for enzyme-substrate reactions at equilibrium.
Formation of 10-Formylfolic Acid, a Potent Inhibitor of Dihydrofolate Reductase, in Rat Liver Slices Incubated with Folic Acid
Authors: d'Urso-Scott M. , Uhoch J. , Bertino J. R.
Published: May 2006

During investigation of folate polyglutamate biosynthesis in rat liver slices utilizing [
2
-
14
C]folic acid, a folate compound that behaved like a polyglutamate form in the Sephadex G-15 gel filtration system was found to accumulate. Subsequent chromatographic, spectral, chemical, and enzymic studies have indicated that the compound formed in liver slices incubated with [
14
C]folic acid with and without methotrexate was 10-formyl folate. This folate is of interest in that it is the most potent natural inhibitor of dihydrofolate reductase known and may be capable of serving a regulatory function within the cell.
The Active Site of Staphylococcal Nuclease: Paramagnetic Relaxation of Bound Nucleotide Inhibitor Nuclei by Lanthanide Ions
Authors: Furie Bruce , Griffin John H. , Feldmann Richard J. , Sokoloski Edward A. , Schechter Alan N.
Published: May 2006

The structure of 3′,5′-thymidine diphosphate bound in the active site of staphylococcal nuclease (EC 3.1.4.7) was studied by measuring the relaxation rate enhancement of substrate analog nuclei by a paramagnetic metal ion. The lanthanide ion, Gd(III), was substituted for Ca(II) in the formation of the ternary complex of nuclease-Gd(III)-3′,5′-thymidine diphosphate. Measurements were made of the transverse relaxation rates of protons and the longitudinal and transverse relaxation rates of the phosphorus nuclei of the bound nucleotide. Internuclear distances between the metal ion and atoms of the 3′,5′-thymidine diphosphate nucleotide were determined from these data by the Solomon-Bloembergen equation. In general, these distances corresponded closely to those determined by previous x-ray crystallography of the thymidine diphosphate complex.

These internuclear distances were also used with a computer program and graphics display to solve for metal-nucleotide geometries, which were consistent with the experimental data. A geometry similar to the structure of the metal-nucleotide complex bound to nuclease determined by x-ray analysis was one of the solutions to this computer modeling process. For staphylococcal nuclease, the nuclear magnetic resonance and x-ray methods yield compatible high resolution information about the structure of the active site. However, differences of uncertain significance exist between the two structures.
Two Types of Molecular Evolution. Evidence from Studies of Interspecific Hybridization
Authors: Wilson A. C. , Maxson L. R. , Sarich V. M.
Published: May 2006

To assess the significance of macromolecular sequence differences among species, we compared the serum albumins of 81 pairs of vertebrate species capable of producing viable hybrids. Micro-complement fixation experiments showed that the average difference between the albumins within such pairs was only 3 immunological distance units for placental mammals (31 pairs), but 36 units for frogs (50 pairs). Albumin immunological distance is strongly correlated with other measures of genetic distance, including those made with DNA annealing techniques. It therefore seems likely that mammalian species pairs capable of hybridization are far more similar at the macromolecular sequence level than is the case for most hybridizable frogs.

We think the most likely explanation for the marked molecular restriction on hybridization among mammals is that the ratio of regulatory evolution to protein evolution is higher for mammals than for frogs. Mammals may have experienced unusually rapid regulatory evolution; indeed, this could be the factor responsible for their unusually rapid anatomical evolution.
Material Isolated from Normal and Variant Human Liver that Immunologically Crossreacts with Alpha
1
-Antitrypsin
Authors: Matsubara Shoji , Yoshida Akira , Lieberman Jack
Published: May 2006

A material that strongly reacts with antibodies against alpha
1
-antitrypsin, but has little trypsin inhibitory capacity, has been isolated and purified to homogeneity from human liver. The molecular weight of the crossreacting material is about 18,000, which is significantly lower than that of serum alpha
1
-antitrypsin. The material isolated from the liver of a homozygous variant subject (
ZZ
) with alpha
1
-antitrypsin deficiency is readily distinguished by electrophoresis from the material extracted from a normal (
MM
) subject. The tissues from a heterozygous variant subject (
MZ
) contain the two components. The immunologically crossreacting material is presumably synthesized by the gene that codes for alpha
1
-antitrypsin.
Cell-Free Translation of Highly Purified Adenovirus Messenger RNA
Authors: Eron Larry , Westphal Heiner
Published: May 2006

Several polypeptides contained in the coat and the core of adenovirus type 2 particles have been identified as virus gene products. They are synthesized
in vitro
by a cell-free protein-making system programmed by adenovirus type 2 messenger RNA that has been hybridized with and eluted from virus DNA. Fractionation by size yields subpopulations of viral messenger RNA that differ in their coding specificities. The procedures outlined in this study may be used to establish a genetic map of adenovirus type 2.
The Localization of Transfer RNA
5
Lys
Genes in
Drosophila melanogaster
Authors: Grigliatti T. A. , White B. N. , Tener G. M. , Kaufman T. C. , Suzuki D. T.
Published: May 2006

Transfer RNA
5
Lys
was isolated and purified from
Drosophila melanogaster
. It was iodinated
in vitro
with sodium [
125
I]iodide and hybridized
in situ
to the polytene salivary gland chromosomes from Drosophila. Autoradiographs exposed three to four weeks allowed the localization of this tRNA to the right arm of chromosome 2 between bands 48F and 49A.
The Influence of Non-Neuronal Cells on Catecholamine and Acetylcholine Synthesis and Accumulation in Cultures of Dissociated Sympathetic Neurons
Authors: Patterson Paul H. , Chun Linda L. Y.
Published: May 2006

The effects of several non-neuronal cell types on neurotransmitter synthesis in cultures of dissociated sympathetic neurons from the new-born rat were studied. Acetylcholine synthesis from radioactive choline was increased 100- to 1000-fold in the presence of non-neuronal cells from sympathetic ganglia. This increase was roughly dependent on the number of ganglionic non-neuronal cells present. The effect did not appear to be due to an increased plating efficiency of neurons, since the non-neuronal cells were capable of increasing acetylcholine synthesis after only 48-hr contact with neurons that had been previously grown without non-neuronal cells for 2 weeks. C6 rat glioma cells were also able to stimulate acetylcholine synthesis, but 3T3 mouse fibroblast cells had little or no effect. None of the non-neuronal cell types synthesized detectable acetylcholine in the absence of the neurons. The ganglionic non-neuronal cells had no significant effect on catecholamine synthesis (which occurs in the absence of non-neuronal cells).
An Analysis of the Cost-of-Selection Concept
Authors: Flake Robert H. , Grant Verne
Published: May 2006

It is shown for a continuous haploid model that the common standard assumptions used in calculating the cost of gene substitution, namely, large constant population size and small constant selective value, are unnecessary. Population size may fluctuate during the course of substitution without affecting the calculated total cost. The selective intensity does not need to be small and constant to give the standard result for substitution cost. Diploid models with multiple alleles are analyzed and contrasted with standard two-allele models in respect to calculation of substitution cost. The influence of population structure on the probability of occurrence of complete gene substitution is discussed on the basis of a numerical example. The robust nature of the cost-of-selection concept is examined in the light of a conservation principle.
An electron microscopic study of virus particles in rhesus monkey placenta.
Authors: Feldman D
Published: May 2006

Examination of chorionic villi from rhesus monkey placenta revealed the presence of C-type virus particles budding from syncytial trophoblast, pericytes, Hofbauer cells, and mesenchyme. In addition, particles, were found budding from cells of the cytotrophoblastic cell column and decidual basalis. They measured 30 nm in diameter, had a dense central core, surrounded by a narrow, electron-lucent zone, and were enclosed by an outer unit membrane.
Temperature-sensitive cell mutations that inhibit adenovirus 2 replication.
Authors: Nishimoto T , Raskas H J , Basilico C
Published: May 2006

Five temperature-sensitive growth mutants of the hamster cell line BHK-21 were tested for the ability to support adenovirus 2 multiplication at 39 degrees and 33 degrees. Wild-type BHK-21 and mutants ts 422E and ts BCH yielded comparable amounts of virus at 33 degrees and 39 degrees, whereas in three other mutants, ts T22, ts T23, and ts AF8, virus production at 39 degrees was reduced to about 1% of that at 33 degrees. Virus yield in the three mutants was not reduced because of a delay in virus production; for all cells tested maximal virus yield at 39 degrees was obtained by 40-50 hr after infection. Normal yields of infectious virus were not obtained from ts AF8 even with a very high multiplicity of infection. In contrast, the virus yield from ts T22 and ts T23 was multiplicity-dependent. Shiftup experiments demonstrated that in ts AF8, a cell cycle mutant which at 39 degrees becomes arrested in G1, virus multiplication was thermosensitive for the first 40 hr of infection. In ts T22 and ts T23, the thermosensitivity was only for the first 3-4 hr of the infection. In all three mutants viral DNA synthesis was reduced by at least 95% at the higher temperature. The cell function specified by the ts AF8 mutation seems to be required for the early period of adenovirus 2 replication, after virus entry into the cell but before the onset of viral DNA replication.
Enzymatic activation and trapping of luminol-substituted peptides and proteins. A possible means of amplifying the cytotoxicity of anti-tumor antibodies.
Authors: Parker C W , Aach R D , Philpott G W
Published: May 2006

Glutathione and glucose oxidase (EC 1.1.3.4) conjugates containing covalently bound luminol were prepared as prototypes for peptides and proteins with latent, enzyme-activatable chemical reactivity. In the presence of small quantities of activated horseradish peroxidase, conjugated luminol molecules were oxidized to unstable free radicals which reacted rapidly with soluble proteins and cells. These observations are of interest in regard to possible sequential localization reactions in which a few molecules of cell-bound antibody-horseradish peroxidase would be used to catalytically alter and trap many molecules of a second (luminol-substituted) enzyme, toxin, or hapten in the same area, as might be desirable in promoting selective cell destruction.
Fate of viral RNA of murine leukemia virus after infection.
Authors: Takano T , Hatanaka M
Published: May 2006

[3H]Uridine-labeled Rauscher leukemia virus was used to infect mouse embryo fibroblasts. After the infected cells were separated into nuclear and cytoplasmic fractions nucleic acid was extracted by sodium dodecyl sulfate-phenol-chloroform treatment and analyzed by Cs2SO4 and sucrose density gradient centrifugation. Between 45 and 70 min after infection a transient and synchronized shift of the acid-insoluble radioactive peak toward the RNA-DNA hybrid region occurred in both the nuclear and cytoplasmic fractions. The density of the cytoplasmic hybrid shifted to 1.56 g/ml (RNA equals about 50%), while the sedimentation rate decreased from 36 S to 14 S; however, the density of the nuclear hybrid shifted to 1.58-1.48 g/ml (RNA equals 57-17%, respectively), while its sedimentation rate remained about 65 S. The hybrids in both the nuclear and the cytoplasmic fractions still showed hybrid density after heat denaturation. The processes of the early stages of RNA tumor virus infection are discussed with regard to the functions of viral RNA-dependent DNA polymerase (reverse transcriptase) and a possible integration of viral genetic information into the host chromosome.
Differentiation in erythroleukemic cells and their somatic hybrids.
Authors: Orkin S H , Harosi F I , Leder P
Published: May 2006

Clones of erythroleukemic cells differ in the extent to which they (1) undergo differentiation spontaneously and (2) can be induced to differentiate in the presence of dimethylsulfoxide. Here we demonstrate that relative differences in globin gene expression within and between clones largely reflect differences in the proportion of cells participating in differentiation rather than uniform differences in the extent to which all cells in these clones undergo differentiation. We call this phenotype of a clone its characteristic probability of differentiation, a property that reflects the likelihood that a cell of this clone will undergo erythrodifferentiation under given conditions. We have examined somatic hybrid cells formed between similar erythroleukemic lines, between phenotypically different erythroleukemic lines, between phenotypically different erythroleukemic lines, and between erythroleukemic cells and mouse fibroblasts. Results of these experiments demonstrate that the spontaneous and induced probabilities of differentiation may be altered in an uncoupled fashion, suggesting that each is determined at different steps leading to a common pathway of globin gene expression.
General almost automorphy
Authors: Bochner Salomon
Published: May 2006

We will propose a very general setting for the following proposition. If a linear operator
Lf
is almost automorphic and all bounded solutions of the homogeneous equation
Lg
= 0 are almost automorphic then, for almost automorphic φ, all bounded solutions of the inhomogeneous equation
Lf
= φ are also almost automorphic.

The almost automorphy previously introduced by us will be generalized and diversified into a property which we will name “
A
-invariance”; and we will deal with both strong solutions and weak solutions. We will also compare our
A
-invariance with minimality, and propose a rather thinned-out almost periodicity that will be associated with our
A
-invariance.
Intramolecular arsanilazotyrosine-248-Zn complex of carboxypeptidase A: a monitor of catalytic events.
Authors: Harrison L W , Auld D S , Vallee B L
Published: May 2006

The intensely chromophoric intramolecular coordination complex formed between arsanilazotyrosine-248 and the active site zinc atom of azocarboxypeptidase A (Johansen, J. T. & Vallee, B. L. (1971) Proc. Nat. Acad. Sci. USA 68, 2532-2535) is a spectrokinetic probe of catalytic events. The interconversion of the azoTyr-248-Zn complex and its constituents is measured by stopped-flow pH and temperature-jump methods. The rate of interconversion, 64,000 sec-1, is orders of magnitude faster than that of the catalytic step itself (about 0.01-100 sec-1). Rapidly turned over peptide and ester substrates disrupt the azoTyr-248-Zn complex before hydrolysis occurs. As a consequence, formation of azoTyr-248, substrate binding, and catalysis can all be monitored while catalysis is actually in progress. The results of these dynamic studies specify a course of catalytic events, different from those postulated based on x-ray structure analysis. If azoTyr-248 is displaced, the direction is opposite to the inward movement postulated on the basis of x-ray studies and is not unique to induction by substrates, since rapid changes in pH also result in analogous spectral changes. AzoTyr-248 carboxypeptidase has all the features which are essential for mechanistic studies: (1) It is enzymatically active; (2) the spectra of the metal complex differ characteristically from those of its constituents; (3) it responds dynamically to environmental factors; and (4) the response time of the probe itself is much more rapid than is required for the measurement of the catalytic step. These combined kinetic and spectral properties of the metal complex render it a powerful spectrokinetic probe to visualize and discern microscopic details of the catalytic process.
Evolution of type C viral genes: preservation of ancestral murine type C viral sequences in pig cellular DNA.
Authors: Benveniste R E , Todaro G J
Published: May 2006

Domestic pigs (Sus scrofa) and other members of the family Suidae have multiple copies of type C viral gene sequences in the cellular DNA of all their tissues. Partially homologous viral gene sequences are also found in cellular DNA of rodents, particularly Muridae. The results lead to the conclusion that type C viral genes were introduced into the Suidae lineage as a result of trans-species infection by an ancestral xenotropic murine virus. The rate of evolution of the virogene sequences in the pig appears to be much slower than that of genes that have remained in the rodent lineage; this may be a consequence of transfer from a shorter-lived animal (the rodent) to a longer-lived one (the pig). We estimate the time of gene transmission as 5-10 million years ago and conclude that the present-day porcine type C virogenes most closely approximate the viral genes as they were several million years ago in the rodent lineage.
Further comments on the ascorbic acid requirement.
Authors: Jukes T H
Published: May 2006

Recommended Daily Allowances (US RDA) of the Food and Drug Administration for ascorbic acid are higher than Recommended Dietary Allowances (set by the Food and Nutrition Board) for adults. There is a 6-fold margin between the requirement to prevent scurvy and the US RDA. The high requirement reported for the rhesus monkey may be needed to compensate for oxidative catabolism of ascorbic acid in this species. The rate of production of ascorbic acid, in mammals that synthesize it has been listed as 3-19 g/70 kg per day. If this high rate of synthesis represents the requirement of such animals, mutations that caused a loss of ascorbic-acid-synthesizing ability would be eliminated by natural selection on diets that failed to supply these large quantities. The loss of ascorbic-acid-synthesizing ability by human beings could indicate a low requirement, which has enabled our species to spread to regions of the earth where dietary sources of ascorbic acid are poor.
Genome-sized RNA from reovirus particles.
Authors: Kavenoff R , Talcove D , Mudd J A
Published: May 2006

Spider-like forms of purified reovirus RNA have been characterized by electron microscopy. These structures contained 11.3 +/- 0.8 mum of double-stranded RNA and up to 20 arms, each of distinct length. Length measurements of 64 "spiders" suggest that in these structures the viral genome is folded fairly specifically.
Selective effects of inhibitors of protein synthesis on metabolism of nuclear anc cytoplasmic proteins: evidence for coordinate synthesis of non-histone chromosomal proteins.
Authors: Vidali G , Karn J , Allfrey V G
Published: May 2006

We have compared the effects of inhibitors of protein synthesis on the metabolism of nuclear and cytoplasmic proteins of HeLa S-3 cells. L-1-tosylamido-2-phenylethyl chloromethyl ketone, a potent inhibitor of polypeptide chain initiation, was shown to preferentially inhibit the synthesis of cytoplasmic proteins and of histones at concentrations that permit continued amino acid incorporation into nuclear non-histone proteins. Comparisons of the molecular weight distributions of newly synthesized proteins in the presence and absence of L-1-tosylamido-2-phenylethyl chloromethyl ketone have revealed striking differences between nuclear anc cytoplasmic protein fractions. Differential effects on the synthesis of cytoplasmic proteins, acid-soluble nuclear proteins, and residual nuclear proteins have also been obtained with the antibiotic, pactamycin, another inhibitor of polypeptide chain initiation. The incorporation of radioactive amino acids into nuclear non-histone proteins shows resistance to inhibition by pactamycin, but is strongly inhibited by agents such as puromycin and cycloheximide which block chain elongation. The possibility that proliferating cells have developed specialized mechanisms for the coordinate synthesis of chromosomal proteins, possibly involving polycistronic messenger RNAs, is tested and discussed.
Allozymic and chromosomal similarity in two Drosophila species.
Authors: Carson H L , Johnson W E , Nair P S , Sene F M
Published: May 2006

D. setosimentum and ochrobasis are a pair of very close, partly sympatric species endemic to Hawaii island. Males of the two species differ strikingly in wing-pattern and there are altitudinal and breeding-site differences. Similarity indices have been calculated for both chromosomal (C) ald allozymic (A) variants. Within the main populations of each species both kinds of data give coefficients above 0.98. Interspecific comparison of the main populations shows 0.66 (C) and 0.79 (A). An isolated population of ochrobasis from Kohala Volcano (Ohu), when compared with setosimentum, shows 0.68 (C) and 0.98 (A). Chromosomes are thus much more sensitive than allozymes in distinguishing these species; the same is true in the case of D. silvestris and heteroneura from the same forests. These morphologically distinct species, when compared, show 0.96 (A). All four species appear to be very new in the historical sense. In one area, about 2% of wild-caught D. setosimentum/ochrobasis are interspecific hybrids although adequate samples indicate that the separate gene pools have not broken down. The specific names should be retained but the two entities are perhaps best described as quite advanced semispecies in which reproductive isolation in nature is now nearly complete.