bluuebunny/crossref_metadata_2025 huggingface dataset:
Protein Chain Initiation by Methionyl-tRNA in Wheat Embryo
Authors: Marcus Abraham , Weeks Donald P. , Leis Jonathan P. , Keller Elizabeth B.
Published: May 2006

The mechanism of protein chain initiation has been investigated in a cell-free amino acid incorporation system from wheat embryos dependent on tobacco mosaic virus RNA. Analysis of the N-termini of the labeled peptide products of short-term incubations showed the presence of unblocked methionine. In addition, methionyl-tRNA (Met-tRNA) could be bound to ribosomes at 1.3 mM Mg
++
in a reaction requiring viral RNA, ATP, GTP, and soluble protein factors.

Incorporation experiments with the two cytoplasmic Met-tRNAs of wheat germ, an initiating species designated Met-tRNA
i
and a Met-tRNA
m
, showed that methionine transfer from Met-tRNA
i
was linear from zero time, while that from Met-tRNA
m
occurred only after an appreciable lag. Analysis of the peptide products showed that methionine transfer from Met-tRNA
i
was predominantly N-terminal. In contrast, methionine transfer from Met-tRNA
m
was exclusively into internal positions. Similar selectivity was observed in the ribosome binding assay; only Met-tRNA
i
showed a strong reaction. These experiments provide strong evidence that in the wheat embryo, cytoplasmic Met-tRNA
i
functions without formylation in the initiation of protein synthesis.
Configuration Interaction in the Calculation of Oscillatory and Rotatory Intensities of Nonplanar π-Electronic Systems
Authors: Cheong Kam-Khow , Oshita Allen , Caldwell Dennis J. , Eyring Henry
Published: May 2006

The interaction of configurations, including all possible singly excited configurations, is incorporated into the calculation of oscillatory and rotatory intensities of simple nonplanar π-electronic systems such as skewed butadiene and acrolein. The results are discussed in terms of the reliability of the (self-consistent field)-(linear combination of atomic orbitals)-(molecular orbital) wave functions employed.
Cell Density-Dependent Changes of Glycolipid Concentrations in Fibroblasts, and Loss of This Response in Virus-Transformed Cells
Authors: Hakomori Sen-itiroh
Published: May 2006

The glycolipids of normal fibroblasts cells at different stages of growth and with differing degrees of susceptibility to contact inhibition have been analyzed, as well as the glycolipids of virally transformed cells. The concentrations (per mg protein) of certain glycolipids, including galactosylgalactosyl-glucosyl-,
N
-acetylneuraminosylgalactosylglucosyl-, and
N
-acetylneuraminosyl-(
N
-acetylneuraminosyl)galactosylglucosyl-c eramide, increase on cell-to-cell contact of susceptible cells. The concentrations of these glycolipids decrease when susceptibility to contact inhibition is lost as a result of extensive passage
in vitro
or transformation by simian virus 40 or polyoma virus, and in all the malignant cells examined, the concentrations of these glycolipids were independent of cell density.
One- and Two-Fluid van der Waals Theories of Liquid Mixtures, I. Hard Sphere Mixtures
Authors: Henderson Douglas , Leonard Peter J.
Published: May 2006

The equation of state of a mixture of hard spheres is calculated using the one- and two-fluid van der Waals theories and the three-fluid theory. The one-fluid theory is found to be in the best agreement with the machine-simulation results.
Abnormal DNA Patterns in Animal Mitochondria: Ethidium Bromide-Induced Breakdown of Closed Circular DNA and Conditions Leading to Oligomer Accumulation
Authors: Nass Margit M. K.
Published: May 2006

Treatment of cultured mouse fibroblasts (L-cells) and hamster kidney cells with ethidium bromide was found to inhibit the incorporation of [
3
H]thymidine into mitochondrial closed-circular DNA, but not into nuclear DNA. The specific activity of nuclear DNA in treated cells was higher than in control cells. Treatment also led to breakdown of closed-circular mitochondrial DNA, greatly enlarged mitochondrial profiles with few or no cristae, and a higher yield of mitochondrial protein per cell.

A significant increase in the content of circular DNA dimers and oligomers of mitochondria was observed after treatment of L-cells with cycloheximide and puromycin or treatment of chick fibroblasts with cycloheximide, and in hamster kidney cells transformed with polyoma virus. Little or no effects on dimer and oligomer content were found in L-cells treated with vinblastine, colcemid, rifampicin, chloramphenicol, or mengovirus, in Rous-transformed hamster cells, or in cuprizone-induced giant mitochondria of rat liver.
Dimerization Mutants of Alcohol Dehydrogenase of Maize
Authors: Schwartz Drew
Published: May 2006

Two ethyl methanesulfonate-induced mutants of the alcohol-dehydrogenase gene in maize have been analyzed. The enzyme subunits produced by the mutants seem to be structurally altered in such a way that the subunit specified by the null allele
Adh
1
0(5657)
does not dimerize with “wild-type” subunits, and that specified by
Adh
1
S(296)
does so only to a limited extent.
Primary Reactions of Photosynthesis: Photoreduction of a Bound Chloroplast Ferredoxin at Low Temperature as Detected by EPR Spectroscopy
Authors: Malkin R. , Bearden Alan J.
Published: May 2006

An electron paramagnetic resonance signal was observed at 25°K in whole spinach chloroplasts after illumination at 77°K. The light-induced epr spectrum had
g
-values (

g
x

= 1.86,

g
y

= 1.94,

g
z

= 2.05) and a temperature dependence that were characteristic of the reduced state of a plant-type ferredoxin. The light-induced epr spectrum was also observed in broken spinach chloroplasts from which soluble ferredoxin was removed. Chemical analyses showed that both whole and broken spinach chloroplasts contained amounts of nonheme iron and “acid-labile sulfide” consistent with the presence of a bound iron-sulfur protein, at a level of about one molecule per 75 chlorophyll molecules. These results support the conclusion that chloroplasts contain a bound ferredoxin that may serve as a primary low-potential electron acceptor in photosynthesis.
Determination of Arterial Blood Flow by Percutaneously Introduced Flow Sensors in an External Magnetic Field, II. Implementation of the Method
In Vivo
Authors: Kolin Alexander , Grollman Julius H. , Steckel Richard J. , Snow Harold D.
Published: May 2006

Blood flow in a dog's aorta has been measured by percutaneous introduction of a flow sensor. Two types of flow probes have been used in conjunction with an external magnetic field: Loop-shaped probes used as rate of volume-flow meters and L-shaped probes as velometers. Methods of calibration and establishing the base line are discussed, and the performance of the apparatus is illustrated by records of blood flow in the thoracic and abdominal regions of the aorta.
The Folded Genome of
Escherichia coli
Isolated in a Protein-DNA-RNA Complex
Authors: Stonington O. Gordon , Pettijohn David E.
Published: May 2006

The DNA of
Escherichia coli
has been isolated in a compact structure containing small amounts of protein and RNA and having a sedimentation coefficient of approximately 3200 S. The molecular weight of the DNA in the complex is very large (probably higher than 10
9
); the protein is predominantly core RNA polymerase; the RNA is chiefly nascent messenger and ribosomal chains. Solutions containing the complex have low viscosities; this plus its sedimentation rate suggest that the DNA is in a tightly folded conformation. The DNA unfolds after exposure to RNase or heat; this indicates that an RNA component of the complex is involved in stabilizing the structure.
The 24th Mersenne Prime
Authors: Tuckerman Bryant
Published: May 2006

The 24th Mersenne prime

M
p

= 2

p

- 1, and currently the largest known prime, is 2
19937
- 1. Primality was shown by the Lucas-Lehmer test on an IBM 360/91 computer. The 24th even perfect number is (2
19937
- 1)·2
19936
.
Optical Activity of Membrane Suspensions: Calculation of Artifacts by Mie Scattering Theory
Authors: Gordon D. J. , Holzwarth G.
Published: May 2006

The circular dichroism, optical rotatory dispersion, and optical density of a suspension of erythrocyte ghosts are calculated from the measured optical properties of solubilized ghosts by classical general scattering theory (Mie theory). The ghost is represented by a solvent-filled spherical shell 7 nm (70 Å) thick and 3.5 μm in radius. The 3- to 5-nm red shifts and unusual band shapes observed in the circular dichroism and optical rotary dispersion of suspensions of the intact ghosts, but not in the solubilized membranes, are reproduced by these calculations. Both differential absorption and differential scattering of left-and right-circularly polarized light contribute significantly to the calculated circular dichroism spectra. The artifacts of small membrane vesicles are shown to be less than those of intact ghosts. It is concluded that the characteristic anomalies in the optical activity of membrane suspensions are artifactual.
Specific Detection of Antigen-Binding Cells by Localized Growth of Bacteria
Authors: Rotman Boris , Cox David R.
Published: May 2006

A new method for the enumeration of lymphoid cells with specific surface-receptors for antigen is described, based on the use of β-D-galactosidase (EC 3.2.1.23), either directly as an antigen or as a conjugated antigen. Binding of β-D-galactosidase is revealed by its activity in releasing riboflavin from a synthetic substrate, riboflavin-β-D-galactopyranoside. The riboflavin, inactive as a vitamin in the galactosidic form, becomes active when released by the enzyme, and can be detected by bioassay. Hence, lymphoid cells with receptors for β-D-galactosidase on their surface can be detected after they have been exposed to the enzyme, washed, and then plated in agar containing riboflavin-β-D-galactopyranoside, streptomycin, riboflavin-
deficient
medium, and a streptomycin-resistant strain of
Streptococcus faecalis
that requires riboflavin. Release of riboflavin is signalled by the growth of characteristic bacterial colonies over the cell that bound β-D-galactosidase.
Rapid Exchange of Subunits between Free Ribosomes in Extracts of
Escherichia coli
Authors: Subramanian Alap R. , Davis Bernard D.
Published: May 2006

The runoff of a mixture of “heavy” and “light” polysomes has been reported to yield hybrid ribosomes, of intermediate density. However, we found that the dissociation of free heavy ribosomes as they advance in a sucrose gradient causes a serious artefact in the demonstration of hybrid ribosomes. This artefact is eliminated by fixation with glutaraldehyde before sedimentation. Formation of hybrid ribosomes can then be demonstrated, but it is equally complete whether the heavy and light preparations are mixed before or after runoff. Hence, free ribosomes exchange subunits rapidly in extracts. The previously reported exchange thus does not provide evidence for formation of free subunits during runoff.
Free-Energy Calculations of the Interactions of Helical Poly(L-Proline) with Water
Authors: Krimm S. , Venkatachalam C. M.
Published: May 2006

Conformational energies, consisting of nonbonded and electrostatic interactions, have been calculated for poly(L-proline) I and II helices, of six-residues length, with a water molecule hydrogen-bonded to each imide group. For polyproline I, the Traub-Shmueli prolyl-ring geometry was used, whereas for polyproline II, calculations were done for the 2 ring geometries of Leung and Marsh and, in some cases, for the several ring geometries of Ramachandran,
et al
. The chain torsion angles ω(N-C′) and Ψ(C
α
-C′) were varied, as were the two angles that specify the orientations of the water molecules. By summation over the latter, it was possible to calculate a free energy at each ω,Ψ that incorporated the conformational entropy of the water molecules. Such ω,Ψ maps reveal that binding of water can cause changes in the equilibrium conformation of polyproline, as well as in the energetics of the chain with respect to ω and Ψ. This has important consequences on the statistics of the chain. Considerations of prolyl-ring self-energies, as well as the conformational entropies of the chains, show that polyproline II is more stable in water than is polyproline I, and determine which ring geometry is favored for polyproline in water.
The “Fallacy” of Maximizing the Geometric Mean in Long Sequences of Investing or Gambling
Authors: Samuelson Paul A.
Published: May 2006

Because the outcomes of repeated investments or gambles involve products of variables, authorities have repeatedly been tempted to the belief that, in a long sequence, maximization of the expected value of terminal utility can be achieved or well-approximated by a strategy of maximizing at each stage the geometric mean of outcome (or its equivalent, the expected value of the logarithm of principal plus return). The law of large numbers or of the central limit theorem as applied to the logs can validate the conclusion that a maximum-geometric-mean strategy does indeed make it “virtually certain” that, in a “long” sequence, one will end with a higher terminal wealth and utility. However, this does not imply the false corollary that the geometric-mean strategy is optimal for any finite number of periods, however long, or that it becomes asymptotically a good approximation. As a trivial counter-example, it is shown that for utility proportional to
x
γ
/γ, whenever γ ≠ 0, the geometric strategy is suboptimal for all T and never a good approximation. For utility bounded above, as when γ < 0, the same conclusion holds. If utility is bounded above and finite at zero wealth,
no
uniform strategy can be optimal, even though it can be that the best uniform strategy will be that of the maximum geometric mean. However, asymptotically the same level of utility can be reached by an infinity of nearby uniform strategies. The true optimum in the bounded case involves nonuniform strategies, usually being more risky than the geometric-mean maximizer's strategy at low wealths and less risky at high wealths. The novel criterion of maximizing the expected average compound return, which asymptotically leads to maximizing of geometric mean, is shown to be arbitrary.
Effects of Adenine Nucleotides on Hydrogen-Ion Transport in Chloroplasts
Authors: McCarty Richard E. , Fuhrman Jonathan S. , Tsuchiya Yoko
Published: May 2006

1-10 μM ATP stimulated H
+
uptake and slowed the release of H
+
in the dark in chloroplasts illuminated at pH values at which photophosphorylation can occur, but not at pH 6.5. This ATP stimulation of H
+
uptake was abolished by an antiserum to the chloroplast coupling factor and was reduced by the energy transfer inhibitors phlorizin and Dio-9. ATP synthesis after illumination was also enhanced by ATP. Electron flow from water to methyl viologen was inhibited by the same low concentrations of ATP.

ADP also increased the extent of H
+
uptake in chloroplasts, even in the presence of arsenate and MgCl
2
. In the presence of hexokinase and glucose, as well as arsenate and Mg
++
, ADP inhibited H
+
uptake. The failure of previous investigators to observe a direct inhibition of H
+
uptake by phosphorylation was probably caused by a masking of the inhibition by the stimulation of H
+
uptake by ATP. Furthermore, the stimulation of H
+
uptake by ATP provides an explanation for its inhibition of electron flow.
Reversible Dissociation of Carbamyl Phosphate Synthetase into a Regulated Synthesis Subunit and a Subunit Required for Glutamine Utilization
Authors: Trotta Paul P. , Burt Michael E. , Haschemeyer Rudy H. , Meister Alton
Published: May 2006

Carbamyl phosphate synthetase (from
Escherichia coli
) consists of a 7.3S protomeric unit that contains one heavy polypeptide chain (molecular weight about 130,000) and one light chain (molecular weight about 42,000). The heavy and light chains were separated by gel filtration in the presence of 1 M potassium thiocyanate. In contrast to the native enzyme and the reconstituted enzyme (prepared by mixing the separated heavy and light chains), the heavy chain does not catalyze glutamine-dependent carbamyl phosphate synthesis, although it does catalyze the synthesis of carbamyl phosphate from ammonia. The heavy chain also catalyzes two of the partial reactions catalyzed by the intact enzyme; i.e., the bicarbonate-dependent cleavage of ATP and the synthesis of ATP from ADP and carbamyl phosphate. Both positive (ammonia, ornithine, IMP) and negative (UMP) allosteric regulatory sites are located on the heavy chain. The only catalytic activity exhibited by the light chain is the hydrolysis of glutamine. A model is presented according to which glutamine binds to the light chain, which is followed by release of nitrogen from the amide group for use by the heavy chain. The findings suggest that glutamine-dependent carbamyl phosphate synthetase (and perhaps other glutamine amidotransferases) arose in the course of evolution by a combination of a primitive ammonia-dependent synthetic enzyme and a glutaminase; this combination may have been associated with a change from ammonia to glutamine as the principal source of nitrogen.
Abnormal Autolytic Enzyme in a Pneumococcus with Altered Teichoic Acid Composition
Authors: Tomasz Alexander , Westphal Monika
Published: May 2006

Pneumococci in which the choline component of the cell wall teichoic acid was replaced by ethanolamine contain an abnormal autolytic enzyme that has a low molecular weight and low activity in contrast to the enzyme typical of choline-containing bacteria that has a high molecular weight and high activity. The abnormal autolysin can be converted to the normal (cholinetype) enzyme by incubation
in vitro
with choline-containing cell walls.
Uptake of Tricarboxylic Acid Cycle Intermediates by Preimplantation Mouse Embryos
In Vitro
Authors: Kramen Martin A. , Biggers John D.
Published: May 2006

Preimplantation mouse embryos were incubated for various periods in the
14
C-labeled intermediates of the tricarboxylic acid cycle, malate, citrate, or 2-oxoglutarate. A marked increase in uptake of these substrates first occurred at the 4-cell stage, the uptake increasing with the length of incubation and the developmental stage of the embryo. In the light of recent observations on ultrastructural changes in mouse embryos with development, studies of mitochondrial transport systems, and the growth of metabolic activities in developing mouse embryos, the increase in accumulation of the tricarboxylic acid cycle intermediates with development may indicate fundamental changes in mitochondrial function that is necessary for further development.
Synthesis and Discharge of the Coupling Factor·Adenosine Diphosphate Complex in Spinach Chloroplast Lamellae
Authors: Roy Harry , Moudrianakis Evangelos N.
Published: May 2006

The formation of a coupling factor·ADP complex is shown to be dependent on photoinduced electron transport, AMP, and P
i
, and sensitive to arsenate and sulfate. The stability of the complex is unaffected by subsequent addition of arsenate, but is quite markedly sensitive to the addition of ADP. The data are discussed in relation to possible models of photophosphorylation, and in particular, to one in which coupling factor-bound, photosynthetically generated, ADP serves as a phosphoryl donor to substrate ADP.
A Cyclic AMP-Dependent Protein Kinase of the Bovine Pineal Gland
Authors: Fontana Joseph A. , Lovenberg Walter
Published: May 2006

A protein kinase that is dependent on cAMP was found to be present in significant amounts in rat and bovine pineal glands. This enzyme system was isolated from bovine pineal glands and shown to consist of two proteins, a kinase and a cAMP-binding protein. The kinase primarily phosphorylates histones and may function in the control of the diurnal variation of the enzymes in the melatonin biosynthetic pathway.
Products of RNA Polymerases in HeLa Cell Nuclei
Authors: Zylber Ester A. , Penman Sheldon
Published: May 2006

RNA polymerase activities in intact HeLa cell nuclei have been examined and compared to activities investigated in previous studies of the purified enzymes. The RNA synthesized by the mammalian polymerases while still in nuclei is identified. The polymerases are tentatively identified by location, sensitivity to α-amanitin, and response to manganese and altered ionic strength. Polymerase I is located in the nucleolus and labels partially complete precursor molecules of ribosomal RNA. Polymerases II and III are in the nucleoplasm and both label giant nuclear heterogeneous RNA.
Adenosine Triphosphate-Induced Sliding of Tubules in Trypsin-Treated Flagella of Sea-Urchin Sperm
Authors: Summers Keith E. , Gibbons I. R.
Published: May 2006

Axonemes isolated from the sperm of the sea urchin,
Tripneustes gratilla
, were briefly digested with trypsin. The digested axonemes retained their typical structure of a cylinder of nine doublet-tubules surrounding a pair of single tubules. The digestion modified the axonemes so that the subsequent addition of 0.1 mM ATP caused them to disintegrate actively into individual tubules and groups. The nucleotide specificity and divalent-cation requirements of this disintegration reaction paralleled those of flagellar motility, suggesting that the underlying mechanisms were closely related. Observations by dark-field microscopy showed that the disintegration resulted from active sliding between groups of the outer doublet-tubules, together with a tendency for the partially disintegrated axoneme to coil into a helix. Our evidence supports the hypothesis that the propagated bending waves of live-sperm tails are the result of ATP-induced shearing forces between outer tubules which, when resisted by the native structure, lead to localized sliding and generate an active bending moment.
Chemical Events in Conducting and Synaptic Membrances during Electrical Activity
Authors: Nachmansohn David
Published: May 2006

Evidence has accumulated in recent years for the central role of proteins and enzymes in the function of cell membranes. In the chemical theory proposed for the generation of bioelectricity, i.e., for the control of the ion permeability changes of excitable membranes, the protein assembly associated with the action of acetylcholine plays an essential role. Support of the theory by recent protein studies in which the excitable membranes of the highly specialized electric tissue were used will be discussed. A scheme is presented indicating the possible sequence of chemical reactions that change ion permeability after excitation. A sequence of chemical events within the excitable membranes of the synaptic junctions, i.e., within the pre- and postsynaptic membranes, similar to that proposed for the conducting membranes, is presented in a second scheme as an alternative to the hypothesis of the role of acetylcholine as a transmitter between two cells.
Mutagenicity to Mammalian Cells of Epoxides and Other Derivatives of Polycyclic Hydrocarbons
Authors: Huberman Eliezer , Aspiras Lourdes , Heidelberger Charles , Grover Philip L. , Sims Peter
Published: May 2006

The cytotoxicity and mutagenicity of several polycyclic hydrocarbons and their K-region derivatives were tested in a clone of Chinese hamster cells; the production of clones resistant to 8-azaguanine was used as the marker for mutagenesis. In the series related to benz(a)anthracene, the K-region epoxide was highly mutagenic, and the phenol was less mutagenic; the hydrocarbon and
cis
and
trans
-dihydrodiols were not mutagenic. Seven resistant clones were isolated and retained their drug-resistance; three of these could be reverted to the wild type. There was no difference in the chromosome numbers among the parent and mutant clones. The results in the methylcholanthrene series were similar to those for benz(a)anthracene. However, in the dibenz(a,h)anthracene series, the phenol was more mutagenic than the epoxide. 7-Methylbenz(a)anthracene epoxide and 7-bromomethylbenz(a)anthracene were highly mutagenic, 7-bromomethyl-12-methylbenz(a)anthracene was less mutagenic, and the parent hydrocarbons were inactive. These results demonstrate that metabolic activation of polycyclic hydrocarbon is required for mutagenic activity in mammalian cells.
Spontaneous Recombination in
Drosophila melanogaster
Males
Authors: Hiraizumi Yuichiro
Published: May 2006

A second chromosome of
Drosophila melanogaster
(symbol
T-007
) isolated from a natural population in Harlingen, Texas, was found to undergo recombination in heterozygous males. Heterozygous males transmit this chromosome with a frequency,
k
, of about 0.4, considerably reduced from the expected value of 0.5. The frequency of male recombination and the
k
value are negatively correlated, indicating that the two phenomena are in some way related. The complementary recombinant products are recovered in equal frequency and the recombination is not restricted to the heterochromatic regions. The time of recombination is not certain, but the distribution of recombinants is more suggestive of meiotic than of premeiotic occurrence. In the natural population of these flies, the frequency of chromosomes with male recombination is 20% or more.
Stochastic Speculative Price
Authors: Samuelson Paul A.
Published: May 2006

Because a commodity like wheat can be carried forward from one period to the next, speculative arbitrage serves to link its prices at different points of time. Since, however, the size of the harvest depends on complicated probability processes impossible to forecast with certainty, the minimal model for understanding market behavior must involve stochastic processes. The present study, on the basis of the axiom that it is the
expected
rather than the known-for-certain prices which enter into all arbitrage relations and carryover decisions, determines the behavior of price as the solution to a stochastic-dynamic-programming problem. The resulting stationary time series possesses an ergodic state and normative properties like those often observed for real-world bourses.
Association of Chromosomal RNA with Repetitive DNA
Authors: Sivolap Yuriy M. , Bonner James
Published: May 2006

Chromosomal RNA, which is a component of the chromosomes of higher organisms, and whose participation is required for sequence-specific interaction of chromosomal proteins with chromosomal DNA, occurs in chromosomes bound to DNA. We have found that the DNA sequences to which chromosomal RNA binds are repetitive ones.
Calculation of the Reaction Cross Section from a Rate Constant by the Method of Steepest-Descent
Authors: Lin S. H. , Eyring H.
Published: May 2006

The reaction cross section of a bimolecular reaction has been calculated from the corresponding rate constant by the inverse Laplace transform. In carrying out the inverse Laplace transform, the method of steepest-descent has been used. As applications, the reaction cross sections for the rate constant of
k
(
T
) =
k
′

T
n
e
-E0/kT

and for the rate constant of the absolute reaction rate theory have been calculated. The computation of the energy density function associated with the definition of the weighted-average cross section has also been discussed.
Inhibition of Serine Proteases by Arylboronic Acids
Authors: Philipp M. , Bender M. L.
Published: May 2006

Arylboronic acids were found to be strong competitive inhibitors of subtilisin and chymotrypsin. The binding constants are strongly pH dependent and give a Hammett-type plot with a slope of -0.885. The pH dependence, the Hammett plot, and nmr model-system studies indicate that inhibition is due to electron-pair donation by the active site histidine to the bound inhibitor.
Nonprotein Amino Acids in the Murchison Meteorite
Authors: Kvenvolden Keith A. , Lawless James G. , Ponnamperuma Cyril
Published: May 2006

Twelve nonprotein amino acids appear to be present in the Murchison meteorite. The identity of eight of them has been conclusively established as
N
-methylglycine, β-alanine, 2-methylalanine, α-amino-
n
-butyric acid, β-amino-
n
-butyric acid, γ-amino-
n
-butyric acid, isovaline, and pipecolic acid. Tentative evidence is presented for the presence of
N
-methylalanine,
N
-ethylglycine, β-aminoisobutyric acid, and norvaline. These amino acids appear to be extraterrestrial in origin and may provide new evidence for the hypothesis of chemical evolution.
Puromycin-Peptide Bond Formation with Reticulocyte Initiation Factors M
1
and M
2
Authors: Shafritz David A. , Laycock David G. , Anderson W. French
Published: May 2006

The ability to form a “peptide” bond between various forms of Met-tRNA or Phe-tRNA and puromycin has been studied in the reticulocyte cell-free system. When Met-tRNA
F
, fMet-tRNA
F
, or
N
-acetylPhe-tRNA are used as substrate at low Mg
++
concentration (3 mM), reticulocyte initiation factors M
1
and M
2
(M
2A
+ M
2B
) are required for puromycin-peptide synthesis. In contrast to bacterial systems, this reaction is also stimulated by the elongation factor T
1
. When Met-tRNA
M
or Phe-tRNA is used as substrate, there is no M-factor requirement for the puromycin reaction; T
1
is absolutely required, and the reaction is stimulated by T
2
. These studies indicate that reticulocyte factors M
1
and M
2
may function in part by placing the initiator tRNA into the P site. The detailed mechanism for mammalian initiation, however, may be more complex than that for bacterial systems.
Substrate Anchoring and the Catalytic Power of Enzymes
Authors: Reuben Jacques
Published: May 2006

Evidence from published nuclear magnetic resonance studies of enzyme-substrate and enzyme-inhibitor systems systems shows that substrates are confined at the active site of the enzyme, have a relatively long residence time, and tumble in solution as an enzyme-substrate complex. The consequences of this “substrate anchoring” with regard to the catalytic power of enzymes are considered. It appears that as a result of the relatively slow motions, the probability of existence of the “activated complex” in the enzymatic reaction may be increased and thus the reaction rate may be accelerated by factors of between 10
6
and 10
9
. It is estimated that the combined effect of substrate anchoring, desolvation, and charge compensation may lead to reaction-rate accelerations by factors of between 10
9
and 10
8
.
Electron Spin Resonance of Chlorophyll and the Origin of Signal I in Photosynthesis
Authors: Norris J. R. , Uphaus R. A. , Crespi H. L. , Katz J. J.
Published: May 2006

A comparison has been made between Signal I, the photo-electron spin resonance signal associated with the primary light conversion act in photosynthesis, and free-radical signals generated in various chlorophyll species
in vitro
. The esr signals obtained from chlorophyll·monomer, (Chl·L)
+.
, chlorophyll dimer, (Chl
2
)
+.
, and chlorophyll oligomer, (Chl
2
)

n

+.
, are broader than Signal I, whereas the chlorophyll-water adduct, (Chl·H
2
O)

n

+.
, gives a signal very much narrower than Signal I. The unusually narrow signal from (Chl·H
2
O)

n

+.
has been ascribed to spin migration, or to unpaired spin delocalization over a large number of chlorophyll molecules. The linewidth of Signal I can be accounted for by a similar delocalization process. A theoretical relationship between the esr linewidth and the number of chlorophyll molecules, N, over which an unpaired spin is delocalized, takes the form ΔH
N
= 1/√N·ΔH
M
, where ΔH
M
is the linewidth of monomer (Chl·L)
+.
. This relationship for N = 2 accounts well for the linewidths of Signal I in green algae, blue-green algae, and photosynthetic bacteria in both the
1
H- and
2
H-forms. The linewidth of Signal I (as well as the optical properties of reaction-center chlorophyll) are consistent with unpaired spin delocalization over an entity containing two chlorophyll molecules, (Chl·H
2
O·Chl)
+.
.
Regulation of Rat Liver Glutamine Synthetase: Activation by α-Ketoglutarate and Inhibition by Glycine, Alanine, and Carbamyl Phosphate
Authors: Tate Suresh S. , Meister Alton
Published: May 2006

Rat liver glutamine synthetase (
s

20,
w

15.0 S; MW about 352,000) resembles ovine brain glutamine synthetase in that it (
a
) has 8 subunits, (
b
) acts on both L- and D-glutamate and certain glutamate analogs (e.g., β-glutamate,
cis
-cycloglutamate, and α-methyl-L-glutamate), and (
c
) is irreversibly inhibited by L-methionine-
S
-sulfoximine. The liver enzyme (but not the brain enzyme) is (
a
) markedly activated by α-ketoglutarate and less so by citrate, and (
b
) inhibited noncumulatively by glycine and alanine, in the presence of Mn
++
but not Mg
++
; inhibition increases with increasing concentrations of glutamate. These regulatory phenomena seem to be correlated with metabolically related enzymes, e.g., glutamine transaminase. Both liver and brain glutamine synthetases are inhibited by carbamyl phosphate (with Mn
++
but not with Mg
++
), which provides a means for controlling glutamine for pyrimidine biosynthesis. Addition of Mn
++
to the Mg
++
-synthetase system, even at Mg
++
: Mn
++
ratios of 1000, markedly inhibits synthesis by both brain and liver enzymes. This finding, and the fact that Mn
++
promotes sensitivity to the negative effectors, indicates that Mn
++
plays a central role in the regulation of glutamine synthetase. Properties of the glutamine synthetases that have been isolated from mammalian, plant, and bacterial cells are compared. They are similar with respect to subunit size, substrate specificity, inhibition by methionine sulfoximine, and Mn
++
-sensitive inhibition by glycine, alanine, and carbamyl phosphate, but differ in certain other regulatory phenomena and in subunit structure.
Mutation and Cancer: Statistical Study of Retinoblastoma
Authors: Knudson Alfred G.
Published: May 2006

Based upon observations on 48 cases of retinoblastoma and published reports, the hypothesis is developed that retinoblastoma is a cancer caused by two mutational events. In the dominantly inherited form, one mutation is inherited via the germinal cells and the second occurs in somatic cells. In the nonhereditary form, both mutations occur in somatic cells.

The second mutation produces an average of three retinoblastomas per individual inheriting the first mutation. Using Poisson statistics, one can calculate that this number (three) can explain the occasional gene carrier who gets no tumor, those who develop only unilateral tumors, and those who develop bilateral tumors, as well as explaining instances of multiple tumors in one eye.

This value for the mean number of tumors occurring in genetic carriers may be used to estimate the mutation rate for each mutation. The germinal and somatic rates for the first, and the somatic rate for the second, mutation, are approximately equal. The germinal mutation may arise in some instances from a delayed mutation.
A New Photosynthetic Pigment, “P430”: Its Possible Role as the Primary Electron Acceptor of Photosystem I
Authors: Hiyama Tetsuo , Ke Bacon
Published: May 2006

The technique of flash kinetic spectrophotometry was used to demonstrate a broad absorption band around 430 nm, which was kinetically different from P700, in several photosystem-I particles from spinach and blue-green algae. The component represented by this absorption band, designated as “P430”, was bleached as fast as P700. Its recovery in the dark was accelerated by ferredoxin and by various artificial electron acceptors with redox potentials as low as -521 mV. The recovery kinetics have been demonstrated to be identical to those of a concomitant reduction of several of the artificial electron acceptors used. Tentatively, “P430” has been proposed as a possible primary electron acceptor of photosystem I.
Localization of the Zinc Binding Site of Aspartate Transcarbamoylase in the Regulatory Subunit
Authors: Rosenbusch Jurg P. , Weber Klaus
Published: May 2006

Aspartate transcarbamoylase (EC 2.1.3.2) from
Escherichia coli
contains six zinc ions per molecule. Renaturation studies of this allosteric enzyme and its isolated subunits show that the metal binding site is in the regulatory polypeptide chain. Ultraviolet difference spectra of the cadmium and zinc derivatives have been used to show that the sites in the isolated subunit and the full enzyme are similar. Results with an apo derivative of the regulatory subunit suggest that the metal is not required for the binding of the feedback inhibitor, but that it is involved in the structural stability of the protein. A close relationship between the reactivity of the cysteine residues in the regulatory subunit and the metal ion has been found.
Proposed Conformation of Oxytocin in Solution
Authors: Urry D. W. , Walter Roderich
Published: May 2006

A conformation of the neurohypophyseal hormone oxytocin in solution is proposed. The structure possesses, in addition to the β-turn comprised of the sequence -L-tyrosyl-L-isoleucyl-L-glutaminyl-L-asparaginyl- in the ring component of the hormonal molecule, a second β-turn involving the C-terminal oxytocin sequence, -L-cysteinyl-L-prolyl-L-leucylglycinamide. The resulting oxytocin structure places the bulky side chains of the leucine and isoleucine residues, as well as the cyclic moiety of the proline residue, at corners of the two β-turns. A critical role is played by the asparagine residue: its peptide N-H participates in the formation of the hydrogen-bonded cyclic structure of the β-turn in the ring component of oxytocin and its peptide C=O can be hydrogen-bonded to the N-H of tyrosine, while its side chain C=O stabilizes the second β-turn by forming a hydrogen bond with the N-H of the leucine residue, which is part of the end peptide of the second β-turn. This conformational assignment of oxytocin is consistent with hydrogen-deuterium exchange studies, with plots of temperature dependence of peptide proton chemical shifts, and with the coupling constants for the NH-CH dihedral angles.
Generalized Predator-Prey Oscillations in Ecological and Economic Equilibrium
Authors: Samuelson Paul A.
Published: May 2006

The standard predator-prey model is generalized beyond the Volterra linear-log form. Conservative oscillations are deduced and also conversion to a variational Hamiltonian form. Generalization to more than two species is also castable into Hamiltonian form, with small vibrations around equilibrium being of undamped sinusoidal type by virtue of associated characteristic exponents all being pure imaginaries. However, introduction into ecological equilibrium of a recognition of limited space and inorganic matter destroys the autonomous periodicity of the motions and makes inapplicable the elegant formalisms of classical statistical mechanics. Introduction of simple diminishing returns leads to damped motions that are kept cyclically alive by shocks of the weather and other exogenous stochastic elements. Introduction of increasing returns solely in an interval near equilibrium leads to autonomous self-exciting oscillations near a stable limit cycle; under stochastic forcing functions, a long-run ergodic state becomes predictable.
Identification of the Essential Light Chains of Myosin
Authors: Dow Jocelyn , Stracher A.
Published: May 2006

The molecular weights of light chains associated with adult and embryonic chick myosin have been determined by polyacrylamide gel electrophoresis in the presence of 0.1% sodium dodecyl sulfate. Adult muscle myosin contains three light chains with molecular weights averaging 27,700, 21,000, and 16,500, while the embryonic form contains only the two largest of these three. Recombination and hybridization experiments have been performed with these samples. The data clearly demonstrate that only two light chains are required for the expression of the full ATPase activity of myosin. The third light chain consistently is associated with adult myosin, but definitive evidence for its role is lacking.
Evidence for Procollagen, a Biosynthetic Precursor of Collagen
Authors: Bellamy Garland , Bornstein Paul
Published: May 2006

Incubation of rat calvaria for short times in the presence of a labeled amino acid revealed the existence of a collagen fraction (procollagen) that functions as a biosynthetic precursor of collagen. Procollagen contains an α1-like chain (pre-α1) that elutes earlier from CM-cellulose than does rat-bone α1 and has a molecular weight, estimated by acrylamide gel electrophoresis, of 120,000. A time-dependent conversion of pre-α1 to α1 was demonstrated by incubation of calvaria for periods varying from 9 to 60 min and by a pulse-chase experiment. Limited cleavage of procollagen with pepsin resulted in a molecule with a chain resembling α1 in chromatographic properties, molecular weight, and relative hydroxyproline and proline contents. Thus, conversion of procollagen to collagen is likely to occur
in vivo
by a proteolytic mechanism. The additional peptide sequences in procollagen may serve to initiate chain association in triple-helix formation, to facilitate molecular transport, and to inhibit intracellular fibrogenesis.
Tricubic Polynomial Interpolation
Authors: Birkhoff Garrett
Published: May 2006

A new triangular “finite element“ is described; it involves the 12-parameter family of all quartic polynomial functions that are “tricubic“ in that their variation is cubic along any parallel to any side of the triangle. An interpolation scheme is described that approximates quite accurately any smooth function on any triangulated domain by a continuously differentiable function, tricubic on each triangular element.
Conformation of Cyclolinopeptide A Observed by Nuclear Magnetic Resonance Spectroscopy
Authors: Brewster Anne I. , Bovey F. A.
Published: May 2006

The 220 MHz spectrum of the cyclic nonapeptide Phe-Phe-Leu-Ile-Ile-Leu-Val-Pro-Pro (all L), designated
cyclolinopeptide A
, is analyzed by decoupling, exchange of peptide NH protons with deuterium, and measurement of the temperature dependence of the NH chemical shift. Measurement of the NH doublet spacings gives values of J
Nα
, the vicinal coupling of α-CH and NH protons of specific amino acid residues. These in turn provide estimates of the rotation angles [unk] about the HN—C
α
H
α
bonds, which in combination with energy minimization studies, allow the determination of the conformation of the main chain. It is concluded that this polypeptide in dimethylsulfoxide solution does not contain intramolecular hydrogen bonds. Deuterium-exchange rates and temperature-dependence studies indicate that of the seven peptide NH protons, five are exposed to solvent, while two, which exchange somewhat more slowly than the others, may be situated in the interior of the ring.
Fluorescence Spectroscopy of an Oriented Model Membrane
Authors: Yguerabide Juan , Stryer Lubert
Published: May 2006

We have devised a simple method that makes it feasible to apply fluorescence techniques to lipid bilayer membranes to elucidate aspects of their structure and dynamics. Fluorescence excitation, emission, and polarization spectra were obtained from a single spherical bilayer membrane consisting of oxidized cholesterol and fluorescent probe. The emission transition moments of
N,N
′-di(octadecyl)oxacarbocyanine and 12-(9-anthroyl)-stearic acid were found to be aligned parallel to the plane of the bilayer, whereas that of
p
-bis-[2-(4-methyl-5-phenyloxazolyl)]-benzene was aligned in a perpendicular direction. All three probes exhibited appreciable rotational mobility, parallel to the plane of the bilayer, in durations of nanoseconds. An attractive feature of this model membrane is that fluorescence measurements can be made at the same time as electrical measurements and perturbations. Also, it may be possible to incorporate functional protein assemblies into this model and to use fluorescence spectroscopy to delineate some aspects of their assembly and function.
Beginnings of Village-Farming Communities in Southeastern Turkey
Authors: Braidwood Robert J. , Çambel Halet , Redman Charles L. , Watson Patty Jo
Published: May 2006

Since the end of World War II, much evidence has accrued of the primary phase of village-farming community life in Southwestern Asia, which began about 7000 B.C. The remains of (usually) several of the positively domesticated animals (dog, sheep, goat, pig) and plants (wheat, barley, legumes such as peas and lentils) assure us that these settlements were based on effective food production, although collected wild foods also remained a significant portion of the human diet. Evidence of a transitional phase (or phases) that must have immediately preceded the primary phase of effective food production has, however, remained very elusive. Part of a breakthrough appears to have been made in the autumn 1970 field campaign at Çaÿonü Tepesi in southeastern Turkey, where the expansion and deepening of earlier exposures has yielded evidence that may span a significant portion of the transition.
Interactions in Colonies of Primitively Social Bees: Artificial Colonies of
Lasioglossum zephyrum
Authors: Michener Charles D. , Brothers Denis J. , Kamm Dwight R.
Published: May 2006

Lasioglossum zephyrum
usually lives in small colonies but is facultatively solitary. Lone bees and colonies produced from female pupae of the same generation were established in artificial indoor nests. Both the length of the prereproductive period and the number of cells produced per bee per day decreased with increasing colony size. In most colonies, ovarially and behaviorally recognized castes arose, a queen and workers, but with all intergradations. The mean size of queens was larger than that of workers. Nearly all queens mated although few workers did so in rooms with a few males, but mating had no effect on subsequent behavior or ovarian development. In groups of diverse age there was a tendency for the oldest bees to be queens; queens also were larger on the average than workers. In groups of equal age, the largest bee was most often queen. As would be expected for a scarcely social species, mechanisms of social integration (resulting in division of labor and differentiation of castes) mostly appear to involve behavioral features of the solitary ancestors and accidental results of joint occupancy of nests. There is no evidence of direct food or pheromone transfer among adult bees.
Evidence for Induction by Cortisol
In Vitro
of a Protein Inhibitor of Transport and Phosphorylation Processes in Rat Thymocytes
Authors: Makman Maynard H. , Dvorkin B. , White Abraham
Published: May 2006

Studies of intact rat thymocytes incubated
in vitro
with cortisol, actinomycin D, puromycin, and cycloheximide indicate that distinct inhibitory effects of cortisol on transport and phosphorylation are due to an action on mRNA synthesis with consequent induction of synthesis of protein(s) with inhibitory influence. Incubation of thymocytes with cortisol results in inhibition of the rate of labeled orthophosphate incorporation into ATP and the entry of rubidium ion and hexoses into the cells. Continuing protein synthesis is required for the progressive and persistent manifestation of the inhibitory effects of the steroid. RNA synthesis is also required during the initial phase of incubation of cells with cortisol, but significant inhibitory effects of cortisol, once initiated, are evident for at least 60-120 min after addition of actinomycin D. In contrast, addition of cycloheximide some time after cortisol results in prevention or reversal of the effects of the steroid. In the absence of cortisol, the antibiotics exert relatively little effect on orthophosphate incorporation and on the transport processes studied. It is suggested that the sequence of events leading to dissolution of thymocytes exposed to cortisol is initiated by the synthesis of mRNA coding for inhibitory protein(s) with more rapid turnover rates than that of the mRNA, and that these events are modulated by the relative sensitivity of different cellular processes to the protein inhibitor(s).