bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Effect in Opal Below Room Temperature
Authors: Buerger Martin J. , Shoemaker Gerald L.
Published: May 2006

Opal, once believed to be amorphous silica, was shown by Levin and Ott (1932,
J. Amer. Chem. Soc.
54, 828-829) to give an x-ray powder pattern of the high-temperature form of cristobalite. The early explanation of this anomalous existence of a phase below its high-low transition temperature is now known to be untenable. One of us suggested that the tiny sizes of the component cristobalite crystals might explain the anomaly; if so, the transition might be expected below ambient temperatures. The record of a du Pont 900 Thermoanalyzer indeed revealed heat effects in opal below ambient temperatures, with an exotherm having a maximum at about -40° on cooling and an endotherm that began about -50° on heating. This was not a latent-heat effect due to the high-low transition of cristobalite, however, for the low-cristobalite pattern persisted to below -50°. Opal normally contains 4-9% water, which is tenaciously held; water loss is nearly linear with temperatures up to about 422°, when water loss is abruptly complete. Water-free opal does not display the thermal effect, but the same opal rehydrated does display it. Water is housed in minute voids, judged to be a few hundred Ångströms across, between minute particles of cristobalite. This water behaves differently from water in bulk, for its begins to melt at about -50°.
Translational Control of Hemoglobin Synthesis by an Initiation Factor Required for Recycling of Ribosomes and for their Binding to Messenger RNA
Authors: Kaempfer Raymond , Kaufman Jennifer
Published: May 2006

The continued recycling of ribosomes during protein synthesis in rabbit reticulocyte lysates at 37° requires an initiation factor whose activity is rapidly lost in the absence of added heme. Partially purified factor (
i
) fully maintains the polysomes; (
ii
) inhibits the association of 40S and 60S ribosomal subunits into single ribosomes; (
iii
) promotes the quantitative entry of added 60S subunits into polysomes; (
iv
) allows the accumulation of ribosomal subunits, instead of single ribosomes, when initiation is blocked with aurin tricarboxylate; and (
v
) is absolutely required for the binding of globin messenger RNA to ribosomes.

These properties suggest that this mammalian initiation factor functions analogously to bacterial IF-3. In addition, the translational control of globin synthesis by heme is exerted, directly or indirectly, through this factor.
Some Thermodynamic Relations at the Critical Point in Liquid-Vapor Systems
Authors: Rice O. K. , Chang Do Ren
Published: May 2006

The relation of the symmetry of the thermodynamic functions with respect to the critical density ρ

c

to the analyticity of the chemical potential above the critical temperature is discussed with the aid of thermo-dynamic considerations. Special consideration is given to the differential coefficients ([unk]
2
μ/[unk]
T
2
)ρ and ([unk]
2
P
/[unk]
T
2
)ρ. The discussion is extended to the two-phase region, and some of the relations between critical exponents are analyzed. A proof is given that the vapor-pressure curve joins smoothly with the critical isochore. The behavior of the entropy along the coexistence curve is considered. Finally, an argument is presented that the Griffiths-Liberman inequality γ′ ≥ β(δ - 1) is an equality.
DNA Nucleotide Sequence Restricted by the RI Endonuclease
Authors: Hedgpeth Joe , Goodman Howard M. , Boyer Herbert W.
Published: May 2006

The sequence of DNA base pairs adjacent to the phosphodiester bonds cleaved by the RI restriction endonuclease in unmodified DNA from coliphage λ has been determined. The 5′-terminal nucleotide labeled with
32
P and oligonucleotides up to the heptamer were analyzed from a pancreatic DNase digest. The following sequence of nucleotides adjacent to the RI break made in λ DNA was deduced from these data and from the 3′-dinucleotide sequence and nearest-neighbor analysis obtained from repair synthesis with the DNA polymerase of Rous sarcoma virus [Formula: see text] The RI endonuclease cleavage of the phosphodiester bonds (indicated by arrows) generates 5′-phosphoryls and short cohesive termini of four nucleotides,
p
A
p
A
p
T
p
T. The most striking feature of the sequence is its symmetry.
Formation of Bimolecular Membranes from Lipid Monolayers and a Study of Their Electrical Properties
Authors: Montal M. , Mueller P.
Published: May 2006

Bimolecular membranes are formed from two lipid monolayers at an air-water interface by the apposition of their hydrocarbon chains when an aperture in a Teflon partition separating two aqueous phases is lowered through the interface. Formation of the membrane is monitored by an increase of the electrical capacity, as measured with a voltage clamp. Electrical resistance of the unmodified membrane is analogous to that of conventional planar bilayers (black lipid membranes) prepared in the presence of a hydrocarbon solvent, i.e., 10
6
-10
8
ohm cm
2
; the resistance can be lowered to values of 10
3
ohm cm
2
by gramicidin, an antibiotic that modifies the conductance only when the membranes are of biomolecular thickness. In contrast to the resistance, there is a significant difference between the capacity of bilayers made from mono-layers and that of hydrocarbon-containing bilayers made by phase transition; the average values are 0.9 and 0.45 μF cm
-2
, respectively. The value of 0.9 μF cm
-2
approximates that of biological membranes. Assuming a dielectric constant of 2.1 for the hydrocarbon region, the dielectric thickness, as calculated from a capacity of 0.9 μF cm
-2
, is 22 Å. This value is 6-10 Å smaller than the actual thickness of the hydrocarbon region of bilayers and cell membranes, as determined by x-ray diffraction. The difference may be due to a limited penetration of water into the hydrocarbon region near the ester groups that would lower the electrical resistance of this region and reduce the dielectric thickness. Asymmetric membranes have been formed by adjoining two lipid monolayers of different chemical composition.
Regulation of Aryl Hydrocarbon Hydroxylase in Intraspecific Hybrids of Human, Mouse, and Hamster Cells
Authors: Wiebel F. J. , Gelboin H. V. , Coon H. G.
Published: May 2006

Microsomal aryl hydrocarbon (benzo{a}-pyrene) hydroxylase is an enzyme complex highly inducible by various substrates. The activity of this enzyme complex was studied in hybrid cell strains obtained from parent cells that differ widely in basal as well as in induced enzyme activity. Hybrid cells were made from mouse fibroblasts, 3T3-4C2, with moderate basal and induced enzyme activity and the L-cell subline, A9, which has no detectable hydroxylase activity. Hybrid A9/3T3-4C2 cells exhibited enhanced basal and induced enzyme activities, which were 2- to 5-fold higher than those in 3T3-4C2 cells. In contrast, intraspecific hybrid cells of the human cell lines, JEC-3 and VA-2, and the hamster cell lines, OBP and BHK, exhibited a reduced basal and induced enzyme activity that was similar to or lower than that of the parent with low enzyme activity. In all hybrid cells examined, an association was observed between basal and induced enzyme activities, suggesting a closely coupled regulation of these activities.
Positive Control of Endolysin Synthesis
In Vitro
by the Gene
N
Protein of Phage λ
Authors: Greenblatt Jack
Published: May 2006

Positive control
in vitro
by gene
N
protein of bacteriophage λ was demonstrated. λ DNA was used to direct
in vitro
synthesis of λ endolysin in a cell-free protein-synthesizing preparation derived from
Escherichia coli
. The endolysin synthesis depends on the concomitant
in vitro
synthesis of λ gene
N
protein. When λ
N
-
DNA was used to direct the cell-free preparation, endolysin was made only if extract was added from cells in which a λ prophage had been induced. The use of various prophage deletion strains proved that if this stimulating activity made
in vivo
is coded by a known λ gene, it must be coded by gene
N
. The ability to stimulate endolysin synthesis
in vitro
on a λ
N
-
DNA template, therefore, constitutes an assay for
N
protein.
Alkylamine-Dependent Amino-Acid Oxidation by Lysine Monooxygenase—Fragmented Substrate of Oxygenase
Authors: Yamamoto Shozo , Yamauchi Takashi , Hayaishi Osamu
Published: May 2006

Lysine monooxygenase catalyzes the oxygenative decarboxylation of L-lysine and produces a corresponding acid amide. L-Alanine was inactive as substrate. However, when propylamine was present, oxidation, but not oxygenation, of alanine was demonstrated with the oxygenase. Alanine was converted to pyruvate, with the liberation of ammonia and hydrogen peroxide, but propylamine remained unchanged. Other α-monoamino acids were also oxidized in the presence of alkylamines with various carbon chain lengths. The highest oxidase activity was observed when the total chain length of both amino acid and amine was nearly identical with that of lysine. Available evidence indicates that the amine-dependent amino-acid oxidase activity is associated with the lysine oxygenase activity.
Selective Inhibition of Growth of Transformed Cells by Protease Inhibitors
Authors: Schnebli Hans Peter , Burger Max M.
Published: May 2006

Five protease inhibitors with different modes of action were found to reduce the growth of transformed mouse (Py3T3, SV3T3, and 3T12) and hamster (PyBHK) cells. Some of these inhibitors caused the transformed cells to cease growth at saturation densities characteristic for nontransformed cells.

The protease inhibitors were strikingly selective with regard to the transformed cells; they had essentially no effect on the growth of the nontransformed cells. From this result, it is concluded that the inhibitors block a protease-like activity that is required for the unrestrained growth of transformed cells.

The inhibitors exerted their effect directly on the cells; they did not affect growth by interacting with serum components of the medium.
Effect of L-Sorbose on Polysaccharide Synthetases of
Neurospora crassa
Authors: Mishra N. C. , Tatum E. L.
Published: May 2006

Neurospora
glycogen synthetase (EC 2.4.1.11) occurs in 100,000 ×
g
particles. The two forms (glucose-6-phosphate dependent-independent) of glycogen synthetase were solubilized and separated by digitonin treatment of the 100,000 ×
g
particles. Glucan synthetase activity of
Neurospora
was found only in a cell-wall preparation. These two enzymes have been characterized in relation to the paramorphogenic action of sorbose. Sorbose-grown cultures showed a marked decrease in the specific activity of both enzymes, as compared to sucrose-grown wild-type cultures. Sorbose inhibited the activity of the wild-type enzymes both
in vivo
and
in vitro
. In the presence of 5 mM sorbose incorporation of [
14
C]glucose from [
14
C]uridinediphosphate glucose into glycogen by the dependent form of glycogen synthetase was completely inhibited. Thus, the paramorphogenic action of sorbose seems to result from its inhibition of these enzymes of cell-wall biosynthesis. Activities of the enzymes from the sorbose-resistant mutant,
patch
, were not affected by sorbose either
in vivo
or
in vitro
.
Barbiturate Interaction with Phosphatidylcholine
Authors: Novak Raymond F. , Swift T. J.
Published: May 2006

A hydrogen-bonding interaction between phenobarbital or pentobarbital with phosphatidylcholine in chloroform is indicated by the effects of added phosphatidylcholine on the infrared and proton magnetic resonance spectra of these barbiturates. The nitrogenbound proton of the barbiturate and the orthophosphate moiety of the phosphatidylcholine molecule appear to be involved. The more pronounced effect with the two barbiturates occurs in the proton magnetic resonance spectra of phenobarbital with increased amounts of phosphatidylcholine. A plot of the chemical shift of phenobarbital N—H against the concentration of phosphatidylcholine is linear and gives an extrapolated shift of 260 Hz (2.6 ppm) at 35°C for a phosphatidylcholine-phenobarbital ratio of unity, pure 1:1 complex. It is suggested that the general depressant nature of barbiturates may be accounted for by their association in a similar fashion with a number of other phosphate-containing molecules.
Herpesviruses and Oncogenesis
Authors: Klein George
Published: May 2006

Herpesviruses have been implicated in oncogenesis. They have been found to be etiologic agents in certain chicken, primate, and frog neoplasms. There is suggestive evidence that herpesviruses may contribute to the genesis of certain human lymphomas.
The Question of the Primary Electron Acceptor in Bacterial Photosynthesis
Authors: Loach P. A. , Hall R. L.
Published: May 2006

An electrophoretic purification of
Rhodospirillum rubrum
photoreceptor subunits prepared by alkaline urea-detergent disruption is described. Completely active photoreceptor subunits with less than 0.30 eq of iron (or any other transition metal) per phototrap can routinely be prepared. A new photoproduced electron paramagnetic resonance (EPR) signal has been detected in these preparations; it was shown to be due to a photoreduced species. It has a
g
-value of 2.0050 ± 0.0003, a peak-peak width of 7.0 ± 0.3 G, and a nearly Gaussian shape. The response of the new signal to microwave power is different from that of the EPR signal of the photoproduced primary electron donor of chromatophores. Quantum yield measurements of spin production show that the new signal is very efficiently formed (ϕ = 0.6) simultaneously with the electron donor radical. No hyperfine structure (down to 0.1 G modulation amplitude) was observed in the new signal, either at room temperature or at the temperature of liquid nitrogen. The possible identity of this molecule is discussed.
Nonprotein Amino Acids from Spark Discharges and Their Comparison with the Murchison Meteorite Amino Acids
Authors: Wolman Yecheskel , Haverland William J. , Miller Stanley L.
Published: May 2006

All the nonprotein amino acids found in the Murchison meteorite are products of the action of electric discharge on a mixture of methane, nitrogen, and water with traces of ammonia. These amino acids include α-amino-
n
-butyric acid, α-aminoisobutyric acid, norvaline, isovaline, pipecolic acid, β-alanine, β-amino-n-butyric acid, β-aminoisobutyric acid, γ-aminobutyric acid, sarcosine,
N
-ethylglycine, and
N
-methylalanine. In addition, norleucine, alloisoleucine,
N
-propylglycine,
N
-isopropylglycine,
N
-methyl-β-alanine,
N
-ethyl-β-alanine α,β-diaminopropionic acid, isoserine, α,γ-diaminobutyric acid, and α-hydroxy-γ-aminobutyric acid are produced by the electric discharge, but have not been found in the meteorite.
Nitrogen Ligands at the Active Site of Alkaline Phosphatase
Authors: Taylor June S. , Coleman Joseph E.
Published: May 2006

The two Zn(II) ions of native
Escherichia coli
alkaline phosphatase (EC 3.1.3.1) that are necessary for activity have been replaced by
63
Cu(II). Titration of apoenzyme with up to 2 eq of Cu(II) gives a homogeneous species with an electron spin resonance typical for Cu(II) in an axially symmetric environment, with

A
z

= 496 MHz,

g
z

=
g
‖ = 2.27, and

g
x

=

g
y

= 2.05. At least seven nitrogen hyperfine lines, spaced 11 G apart, are clearly resolved on the
M
= +[unk] Cu(II) hyperfine peak in the parallel region. When more than 2 eq of Cu(II) are added, the electron spin resonance spectrum shows at least two types of Cu(II) binding sites; the additional site, or sites, are characterized by lower
g
and higher

A
z

values. When Cu(II) is added to native Zn(II) alkaline phosphatase or to apoenzyme incubated with 2 eq of Zn(II), the electron spin resonance spectrum shows little or no trace of the species with higher
g
values and nitrogen splitting. These results indicate that the species with higher
g
represents copper bound at the site normally occupied by the 2 Zn (II) ions necessary for enzyme activity, and that the metal ion at this site has at least 3 equivalent nitrogen ligands, probably histidyl side chains.
Translation of Avian Myeloblastosis Virus RNA in a Cell-Free Lysate of
Escherichia coli
Authors: Siegert W. , Konings R. N. H. , Bauer H. , Hofschneider P. H.
Published: May 2006

In a cell-free extract of
E. coli
, RNA from avian myeloblastosis virus directs the synthesis of a protein that is antigenically identical with the group-specific antigen 4, and other proteins, three of which correspond in molecular weight to group-specific antigens 1-3.
Translational Restarts: AUG Reinitiation of a
lac
Repressor Fragment
Authors: Platt Terry , Weber Klaus , Ganem Don , Miller Jeffrey H.
Published: May 2006

An early, spontaneous amber mutation in the
lac i
-gene allows translational reinitiation, which results in a mutant
lac
repressor. Comparison of the amino-terminal sequence of this mutant repressor with the partial amino-acid sequence of the wild-type
lac
repressor shows that reinitiation occurs at the first internal AUG codon, and results in a mutant protein lacking 42 residues at the amino-terminal end. This protein binds the inducer isopropyl-β-D-thiogalactoside with normal affinity, and is capable of maintaining a tetrameric structure; however, it does not repress
in vivo
. These data suggest that the amino-terminal portion of the wild-type
lac
repressor is necessary either for direct binding to the
lac
operator or for the correct conformation for binding to DNA.
Weak Compactness and Control Measures in the Space of Unbounded Measures
Authors: Brooks James K. , Dinculeanu Nicolae
Published: May 2006

We present a synthesis theorem for a family of locally equivalent measures defined on a ring of sets. This theorem is then used to exhibit a control measure for weakly compact sets of unbounded measures. In addition, the existence of a local control measure for locally strongly bounded vector measures is proved by means of the synthesis theorem.
Significant Liquid-Structure Theory of Viscosity and Self-Diffusion of the Alkali Metals
Authors: Hsu Chen C. , Eyring Henry
Published: May 2006

Significant liquid-structure theory has been used to calculate the transport properties of the alkali metals. Unlike previous calculations, the volume and temperature dependence of the solid-like structure has been taken into consideration. Equations for the potential energy as a function of volume of the alkali metals, which lead to agreement between calculated and experimental values of thermodynamic and transport properties, are given. The calculated results are in satisfactory agreement with the experimental data.
Spin-Label Studies of Dynamics of Lipid Alkyl Chains in Biological Membranes: Role of Unsaturated Sites
Authors: Eletr S. , Keith Alec D.
Published: May 2006

Cultures of a yeast mutant, deficient in the synthesis of unsaturated fatty acids, were supplemented with either stearolic acid or with any one of three octadecanoic acids having a
cis
double bond 6, 9, or 11 carbons away from the acyl group. The resulting cells, with lipid alkyl chains well defined with respect to the position and nature of unsaturated sites, were then studied with spin-labeled stearic acids having a
N
-oxyloxazolidine ring located at 4, 6, 9, or 12 carbons away from the acyl group, and added
in vitro
to the cellular preparations.

Differences in the molecular motion of each spin label were observed, as a function of the unsaturated site, in the intact yeast cells. Characteristic order to disorder phase transitions are inferred from data of temperature dependence. The results also indicate that triple bonds and
cis
double bonds inhibit a relatively ordered packing of lipid alkyl chains in the region between unsaturated sites and terminal methyl groups, leaving the hydrophobic region bounded by acyl groups and unsaturated sites unaffected.
Cytochalasin B: Inhibition of Glucose and Glucosamine Transport
Authors: Estensen Richard D. , Plagemann Peter G. W.
Published: May 2006

Cytochalasin B has been shown to potently inhibit the transport of glucose, deoxyglucose, and glucosamine by Novikoff hepatoma cells in suspension culture without affecting their intracellular phosphorylation and metabolism. Deoxyglucose transport is inhibited by cytochalasin B in a simple competitive manner. Although this inhibition is not sufficient to explain the biological action of the drug on cytokinesis, it does explain earlier observations on inhibition by cytochalasin B of the incorporation of glucose and glucosamine, and probably of other extracellular precursors, into macromolecules by various types of cells.
Circadian Systems: Longevity as a Function of Circadian Resonance in
Drosophila melanogaster
Authors: Pittendrigh Colin S. , Minis Dorothea H.
Published: May 2006

Drosophila melanogaster
, which had been reared under standard conditions (25° and a 24-hr light/dark cycle involving 12 hr of light) were exposed, on the first day of adult life, to four environments (all at 25°) as follows: (
i
) a 24-hr day consisting of 12 hr light and 12 hr dark; (
ii
) a 21-hr day (10.5 hr light, 10.5 hr dark); (
iii
) a 27-hr day (13.5 hr light, 13.5 hr dark); and (
iv
) constant light. The experiment was repeated four times. In all four experiments the flies on a 24-hr day lived significantly longer than the flies in the other environments. This result, comparable to other observations on plants, indicates that eukaryotic systems as oscillators perform most effectively when they are driven close to their natural “circadian” frequency.
Circadian Rhythms in Drinking Behavior and Locomotor Activity of Rats Are Eliminated by Hypothalamic Lesions
Authors: Stephan Friedrich K. , Zucker Irving
Published: May 2006

Bilateral electrolytic lesions in the suprachiasmatic nuclei permanently eliminated nocturnal and circadian rhythms in drinking behavior and locomotor activity of albino rats. The generation of 24-hr behavioral rhythms and the entrainment of these rhythms to the light-dark cycle of environmental illumination may be coordinated by neurons in the suprachiasmatic region of the rat brain. Destruction of the medial preoptic area had no effect on 24-hr drinking rhythms.
β
2
-Microglobulin—A Free Immunoglobulin Domain
Authors: Peterson Per A. , Cunningham Bruce A. , Berggård Ingemar , Edelman Gerald M.
Published: May 2006

Analysis of the primary structure of β
2
-microglobulin indicates that this human protein is homologous in sequence to the constant portion of immunoglobulin light chains (C
L
), and to the homology regions (C
H
1, C
H
2, and C
H
3) of the constant portion of γ1 (heavy) chains of immunoglobulin G. Homology with the C
H
3 region is particularly striking. No convincing homology could be demonstrated by similar comparisons with the variable regions of immunoglobulin light and heavy chains. β
2
-Microglobulin contains an intrachain disulfide loop of 57 amino-acid residues that is similar in size to disulfide loops found in the constant regions of immunoglobulin G. These findings suggest that β
2
-microglobulin is a free immunoglobulin domain, possibly serving an effector function similar to that of the C
H
3 domain of γ1 chains of immunoglobulin G.
The Binding of [
3
H]Thyrotropin and an
3
H-Labeled Exophthalmogenic Factor by Plasma Membranes of Retro-orbital Tissue
Authors: Winand Roger J. , Kohn Leonard D.
Published: May 2006

Plasma membranes of cells from retroorbital tissue have been prepared from the Harderian glands of guinea pigs and have been characterized as being reasonably free of other subcellular structures by electron microscopy and by enzyme-marker analyses. Both bovine thyrotropin and a proteolytic derivative of bovine thyrotropin with exophthalmogenic activity but without thyroid-stimulating activity specifically bind to these membranes. Gammaglobulin from the sera of patients with malignant exophthalmos increases the binding of both pituitary factors, whereas binding is not similarly increased by gammaglobulin from the sera of individuals who are not exophthalmic. The increased binding caused by the gammaglobulin from exophthalmic patients is the same whether the sera are positive or negative for the long-acting thyroid stimulator. Present binding experiments do not indicate a direct interaction between the gammaglobulin and the plasma membranes of the cells from Harderian glands. A mechanism for the pathogenesis of human exophthalmos is proposed on the basis of these data.
Bifurcation Theory and the Type Numbers of Marston Morse
Authors: Berger Melvyn S.
Published: May 2006

Let
H
be a real Hilbert space and
f
(
x
,λ) be a
C
2
operator mapping a small neighborhood
U
of (
x
0
,λ
0
) ε (
H
× R
1
) into itself. We investigate the solutions of the equation
f
(
x
,λ) = 0 near a solution (
x
0
,λ
0
), assuming that
f
(
x
,λ) is a gradient mapping and 0 < dim Ker

f
x

(
x
0
,λ
0
) < ∞. In particular, we show that the type numbers of Marston Morse for an isolated critical point can be used to prove the existence of a point of bifurcation at (
x
0
,λ
0
). An application of this result is given to the discovery of periodic motions near a stationary point for a large class of nonlinear Hamiltonian systems in “resonant” cases.
Identification of Lactate Dehydrogenase Isoenzymes by Rapid Kinetics
Authors: Bishop Michael J. , Everse Johannes , Kaplan Nathan O.
Published: May 2006

Stopped-flow kinetics indicate that human and chicken heart-type
4
lactate dehydrogenases (LDH) become inhibited as DPNH is oxidized in the presence of high concentrations of pyruvate. This inhibition is much less marked with the human and chicken muscle-type
4
enzymes. The initial rates and the difference in inhibition between the two types of enzyme have made it possible to determine the amount of, as well as the ratio between, the two types of LDH that are present in a given sample by a single kinetic assay. The stopped-flow kinetic method has been used to analyze amounts of LDH isoenzyme in different tissues, as well as in serum.
Characterization by Electron Microscopy of Fused F-Prime Factors in
Escherichia coli
Authors: Palchaudhuri S. R. , Mazaitis A. J. , Maas W. K. , Kleinschmidt A. K.
Published: May 2006

During previous attempts to find mutants in which incompatibility between two F-prime (F′) factors of
E. coli
is abolished, we found that two F′ factors harbored in the same cell occasionally recombined to form a single genetic unit. Thus, a fused F′
trp
+
arg
+
factor was obtained from a mating of a strain carrying
recA
F′
trp
+
with a strain carrying
recA
F′
arg
+
. In the present paper physical fusion of the two F′ factors, inferred from genetic studies, is confirmed by electron microscopy. F DNA was extracted, after detergent lysis, from four fused F′ strains: the parental F′
trp
+
and F′
arg
+
strains and three F
+
strains. This supercoiled DNA was separated on ethidium bromide-cesium chloride gradients and converted to the open circular from before electron microscopy. The contour lengths in μm of the various DNA preparations were: F′
trp
+
, 59.4; F′
arg
+
, 33.2; the four F′
trp
+
arg
+
factors, 38.5, 39.6, 63.2, and 73.5: the three F factors, 31.1, 31.1, and 31.0. Thus, different fused F′ factors formed from the same parental F′ factors vary in length, but are shorter than the sum of the parental F′ factors.
Association of Actinomycin D and Deoxyribodinucleotides as a Model for Binding of the Drug to DNA
Authors: Krugh Thomas R.
Published: May 2006

The association of actinomycin D and eleven different deoxyribodinucleotides were studied as model complexes for the interaction of actinomycin D and DNA. All of the deoxyribodinucleotides containing guanine will complex with actinomycin D, and the guanine base has a preferred orientation with respect to the chromophore of actinomycin D. The spectrophotometric binding curve for pdG-dC is sigmoidal (Hill constant = 2.0 ± 0.2), while the binding curves of all other dinucleotides of the form pdN-dG are hyperbolic. The equilibrium expression for the complex with pdG-dC was second order in dinucleotide concentration, with
K
App
= 1.7 × 10
7
liter
2
/mol
2
, while the binding of pdC-dG was first order in dinucleotide concentration, with
K
App
1.8 × 10
3
liter/mol. The sigmoidal pdG-dC binding curve shows that actinomycin D has a preference for G-C sequences of DNA as potential binding sites.
Filament Formation by Purified
Physarum
Myosin
Authors: Nachmias Vivianne
Published: May 2006

Physarum
myosin can be separated from actomyosin by ultracentrifugation, and purified by gel filtration. Unlike actomyosin, myosin is soluble in 0.05 M KCl in the pH range of 6-7. However, in the absence of actin, the slime mold myosin can be precipitated in 0.05 M KCl by the addition of millimolar concentrations of CaCl
2
. The precipitates consist of aggregated, short bipolar filaments. Magnesium has a similar effect, but results in the precipitation of more loosely packed aggregates.

The length of the compact filaments is 0.45 μm; thus, predominantly tail-to-tail, but also some head-to-tail, interactions occur under these conditions. Since the size and shape of these thick filaments are close to those seen in fixed and sectioned ameboid cells and in platelets, all of these filaments are probably composed of myosins.
Stimulation of Chondromucoprotein Synthesis in Chondrocytes by Extracellular Chondromucoprotein
Authors: Nevo Zvi , Dorfman Albert
Published: May 2006

Chondrocytes in suspension culture preserve their differentiated state, as expressed by a high rate of chondromucoprotein synthesis. Purified chondromuco-protein added to a suspension of cultured embryonic epiphyseal cartilage cells stimulates the rate of synthesis of chondromucoprotein at concentrations up to 2 mg/ml. The stimulation involved synthesis of the entire molecule since incorporation of labeled serine (into core protein), glucosamine, acetate, or sulfate was increased. Neither the amount of synthesis of total protein nor that of collagen was increased. No elevation of xylosyltransferase and
N
-acetylgalactosaminyltransferase activities was observed. The stimulation was produced by several other polyanionic substances. No evidence was found of the entry of chondromucoprotein into chondrocytes under the conditions of the experiments. Mild trypsinization lowered the response to added chondromucoprotein and decreased the endogenous rate of chondromucoprotein synthesis. Incubation of cells after trypsinization results in restoration of the rates of chondromucoprotein synthesis. The endogenous, as well as the stimulated, rate of chondromucoprotein synthesis varied with the density of chondrocytes in culture. It is suggested that the rate of chondromucoprotein synthesis may be partially controlled by cell surface receptors.
Resolution of a Spectrum of Nucleoprotein Species in Sonicated Chromatin
Authors: Reeck Gerald R. , Simpson Robert T. , Sober Herbert A.
Published: May 2006

Sonicated rabbit-liver chromatin is fractionated by ion-exchange chromatography on ECTHAM-cellulose, a weakly cationic adsorbent. The chromatographic procedure provides a series of fractions having a spectrum of thermal denaturation profiles. The earliest-eluting fractions melt cooperatively at a significantly higher temperature than bulk chromatin, and totally lack any of the components of chromatin that melt at low temperatures. In contrast, the latest-eluting fractions are significantly enriched in their content of DNA sequences that melt at low temperatures. Although the protein to DNA mass ratio of all fractions is equal to that of unfractionated chromatin, polyacrylamide gel electrophoresis demonstrates that the relative amounts of individual proteins vary across the chromatographic peak. The most pronounced changes observed are the enrichment of a particular high molecular weight nonhistone protein in the later fractions, and a significant diminution of lysine-rich histone in the last fractions. The results, in conjunction with the demonstration by McConaughy, B. L. & McCarthy, B. J. (
Biochemistry
11, 998-1003, 1972) that RNA transcribed
in vivo
in immature chick erythrocytes hybridizes to the DNA of only the portions of chromatin from these cells that melt at low temperatures, suggest that this fractionation may separate transcribable DNA sequences in chromatin from the repressed segments of a eukaryotic genome.
Isolation of a Pyrophosphoryl Form of Pyruvate, Phosphate Dikinase from Propionibacteria
Authors: Milner Yoram , Wood Harland G.
Published: May 2006

Pyruvate, phosphate dikinase from
Propionibacterium shermanii
catalyzes the formation of P-enolpyruvate, AMP, and inorganic pyrophosphate from pyruvate, ATP, and orthophosphate; the mechanism involves three partial reactions and three forms of the enzyme: pyrophosphoryl-enzyme, phosphoryl-enzyme, and free enzyme. The phosphoryl-enzyme was prepared by incubation with P-enolpyruvate and isolated by gelchromatography. The phosphoryl-enzyme was converted to
32
P
31
P-enzyme and [
32
P]Pi by incubation with [
32
P]PPi; 1 mol of pyrophosphoryl-enzyme was formed per mol of enzyme of molecular weight 150,000. The labeled enzyme released its radioactivity upon incubation with Pi or AMP to produce the expected [
33
P]PPi or [γ-
32
P]ATP, respectively. Hydrolysis of the pyrophosphoryl-enzyme with dilute acid yielded PPi. The β,γ-methylene analogue of ATP was reactive in exchange reactions with [
14
C]AMP. To our knowledge, this is the first proven example of a pyrophosphoryl-enzyme.
DNA-Directed Synthesis
In Vitro
of T4 Phage-Specific Enzymes
Authors: Natale Peter J. , Buchanan John M.
Published: May 2006

The synthesis of deoxynucleotide kinase (EC 2.7.4.2)
in vitro
by a preparation consisting of T4 bacteriophage DNA and a cell-free extract of
Escherichia coli
has been reported. A study of the role of monovalent cations in the synthesis of this enzyme as well as α-glucosyl transferase (EC 2.4.1.2) shows that potassium ions are required for maximal enzyme production. Examination of the RNA-directed system indicates that potassium ions are more effective than ammonium ion in the translation of messenger RNA for the formation of the biologically active proteins studied. From a comparison of the magnitude of the effect of ions on both the DNA- and RNA-directed systems, we conclude that potassium ions may also have a marked stimulatory effect on transcription of the deoxynucleotide kinase gene of T4 DNA. The time required for messenger initiation and completion and the size distribution of messenger RNA formed
in vitro
were also examined.
Thymus-Independence of Slowly Metabolized Immunogens
Authors: Sela Michael , Mozes Edna , Shearer G. M.
Published: May 2006

The role of thymus in antibody responses to a series of four synthetic polypeptide immunogens of the general formula multi-copoly(Tyr,Glu)-poly(Pro)-poly(Lys) was investigated as a function of the optical activity of the amino acids composing their structure. Irradiated nonthymectomized and thymectomized SJL mice were injected with thymocytes, marrow cells, or a mixture of both. Each group of recipients was immunized with the following copolymer enantiomorphs: all L-amino acids; L-amino acids outside and D inside; D-amino acids outside and L inside; or all D-amino acids. The antibody response to the immunogen composed of all L-amino acids was thymus-dependent, whereas the responses to the other three copolymers were all independent of the thymus. Similar cell transfers were performed in DBA/1 mice immunized with multi-copoly(L-Phe,L-Glu)-poly(D-Pro)-poly(D-Lys). This mouse strain produces specific antibodies against the (Phe,Glu) region and against the poly(D-prolyl) region. The immune response to the determinant with only L-amino acids on the outside was thymusdependent, whereas the response to the inside immunopotent region with only D-amino acids was thymusindependent. Since earlier studies have demonstrated that synthetic polypeptide antigens that contain D-amino acids are poorly metabolized, the thymus-independence of the antibody responses to these multichain synthetic polypeptides that possess repeating antigenic determinants was correlated with the metabolizability of the immunogens or their component determinants.
Specific Suppression of the Antibody Response by Antibodies to Receptors
Authors: Cosenza Humberto , Köhler Heinz
Published: May 2006

Balb/c myeloma proteins, TEPC 15 and MOPC 167, bind phosphorylcholine and precipitate with the C-polysaccharide moiety of pneumococci R36A. Anti-idiotypic antibodies to TEPC 15 myeloma raised in A/He mice prevent plaque formation by cells releasing antibody to phosphorylcholine and inhibit induction of the antibody response to phosphorylcholine
in vitro
and
in vivo
. This suppression is specific since antibodies against non-crossreacting idiotypic determinants of MOPC 167 do not prevent either formation of plaques or induction of the antibody response. Furthermore, the response to sheep erythrocytes is not suppressed by antibodies to TEPC 15. These results indicate that antibodies to phosphorylcholine and cell receptors for phosphorylcholine share similar antigen-binding sites with TEPC 15 myeloma protein. Thus, anti-idiotypic antibodies directed against TEPC 15 myeloma protein function as “anti-receptor” antibodies since they specifically prevent induction of the primary response to phosphorylcholine. It is proposed that antibodies to receptors may be involved in the homeostasis of the immune response.
The Use of Dopamine β-Hydroxylase as a Marker for the Central Noradrenergic Nervous System in Rat Brain
Authors: Hartman Boyd K. , Zide Doris , Udenfriend Sidney
Published: May 2006

Improvements in the method for localization of dopamine-β-hydroxylase by immunofluorescence allow the observation of noradrenergic-cell bodies, non-terminal fibers, and axon terminals in the rat brain. The distribution of the hydroxylase correlated well with the results obtained by localization of norepinephrine. Dopamine-β-hydroxylase was not observed in dopaminergic neurons or terminals, indicating that these cells do not have the capacity to synthesize norepinephrine. The use of the hydroxylase as a marker, however, has made it possible to visualize noradrenergic nerve terminals on small arteries in the brain parenchyma that have not been described by catecholamine-fluorescence histochemistry. The source of the terminals on small arteries appears to be central noradrenergic neurons rather than the peripheral sympathetic nervous system. Dopamine-β-hydroxylase generally was not observed in the large arteries of the brain parenchyma. These observations suggest that cerebral microcirculation is regulated by central noradrenergic neurons.
Inhibition of RNA-Dependent DNA Polymerase of Rous Sarcoma Virus by Thiosemicarbazones and Several Cations
Authors: Levinson Warren , Faras Anthony , Woodson Bruce , Jackson Jean , Bishop J. Michael
Published: May 2006

The RNA-dependent DNA polymerase of Rous sarcoma virus is inhibited by
N
-methyl isatin β-thiosemicarbazone and by thiosemicarbazide, but not by semicarbazide. These inhibitors also inactivate, upon contact with the virion, the transforming ability of Rous sarcoma virus. Sulfhydryl donors, such as 2-mercapto-ethanol, can prevent these effects. The RNA-directed activity of the purified polymerase is inhibited to a greater degree than is the DNA-directed activity.

Two cations, Cu
++
and Hg
++
, can inhibit RNA-dependent DNA polymerase and inactivate the transforming ability of the virus. Synergism between
N
-methyl isatin β-thiosemicarbazone and Cu
++
occurs, since treatment of the virus with a low dose of either
N
-methyl isatin β-thiosemicarbazone or Cu
++
has little effect; however, when the two compounds are mixed together, significant inactivation occurs. This observation supports the hypothesis that the antiviral action of thiosemicarbazones is a function of their ability to act as a ligand for metallic ions.

Several cations (Ag
+
, Co
++
, Zn
++
, Cd
++
, and Ni
++
) significantly inactivate the RNA-dependent DNA polymerase, but have little effect on the transforming ability. In view of this result, the conclusion that the enzyme activity is required for transformation remains open to question.
Inhibition of Reticulocyte Peptide-Chain Initiation by Pactamycin: Accumulation of Inactive Ribosomal Initiation Complexes
Authors: Kappen Lizzy S. , Suzuki Hideo , Goldberg Irving H.
Published: May 2006

Pactamycin does not inhibit the overall initiation factor- and GTP-dependent binding of [
35
S]Met-tRNA

f

to rabbit reticulocyte ribosomes but does prevent the formation of Met-puromycin, provided that the antibiotic is present during the course of the binding reaction. These data indicate that pactamycin blocks the synthesis of a functional peptide-chain initiation complex. Sucrose density gradient centrifugation analysis of binding reactions shows that pactamycin causes the accumulation of an initiation complex on the smaller ribosomal subunit (smaller initiation complex), to which the 60S ribosomal subunit either cannot join or with which it forms a larger inactive 80S initiation complex that falls apart under the conditions used for isolation. The smaller initiation complex formed in the presence of pactamycin differs from the normal intermediate in peptide-chain initiation in being much more resistant to degradation by pancreatic RNase. In the presence of pactamycin, the inactive smaller complex can also form on mRNA to which an unaffected ribosomal couple is already attached, forming an oligoribosome lacking a larger ribosomal subunit or a “1.5 mer.” These effects of pactamycin can be overcome to a considerable degree by elevation of the Mg
2+
concentration.
A Single Subunit from Avian Myeloblastosis Virus with Both RNA-Directed DNA Polymerase and Ribonuclease H Activity
Authors: Grandgenett Duane P. , Gerard Gary F. , Green Maurice
Published: May 2006

Two structurally distinct forms of RNA-directed DNA polymerase from avian myeloblastosis virus were resolved by chromatography on phosphocellulose and purified. In addition to RNA-directed DNA polymerase activity, both enzymes had ribonuclease H (RNase H) activity, which degraded the RNA moiety of RNA·DNA hybrids. As determined by sodium dodecyl sulfate-polyacrylamide disc-gel electrophoresis, one form had two subunits, alpha (α) and beta (β), with molecular weights of 65,000 and 105,000, respectively. The other had a single subunit, α, with a molecular weight of 65,000. The sedimentation coefficients of αβ and α, determined by glycerol gradient centrifugation in 0.35 M KCl, were 7.8 S and 5.2 S, respectively. Both enzymes had similar antigenic determinants and could not be distinguished by a differential response to several different RNA and DNA templates. We suggest that α, which contains both RNA-directed DNA polymerase and RNase H activity, is derived by dissociation of αβ; the function of the β subunit is unknown.
Theory of Muscular Contraction Extended to Groups of Actin Sites
Authors: Hill Terrell L.
Published: May 2006

It was shown in an earlier paper how to connect, in principle, the biochemical states of a cross-bridge with the mechanics of muscular contraction, by the methods of statistical mechanics. The treatment applies to cross-bridges that are able to interact with only one actin site at a time. The present paper shows that it is a straightforward matter to extend the theory to groups of actin sites (three, five, etc.), say 55 Å apart, as suggested by the work of Moore, H. E. Huxley, and DeRosier. The possibility of the cross-bridge attachment slipping between sites is included. This provides an alternative molecular interpretation of the model introduced by A. F. Huxley and Simmons. A second possible interpretation is also suggested: their discrete stable angles correspond to different biochemical (attached) states. The Huxley-Simmons analysis of an example is rederived and extended somewhat (
x
averaging), from the point of view of the present theory. Their qualitative conclusions are left unchanged by the
x
averaging, but significant quantitative effects are possible. Possible consequences of fast slipping in isotonic contraction are discussed in a preliminary way.
The Molecule Microscope: A New Instrument for Biological and Biomedical Research
Authors: Weaver James C. , King John G.
Published: May 2006

We describe a new instrument, the molecule microscope, which reveals directly spatial variations in the rate of evaporation of molecules from surfaces by using neutral molecules instead of light or charged particles used in existing kinds of microscopes. The surface composition of the sample determines the binding energy of the evaporating molecules and, hence, the rate of evaporation, which also depends on permeability of the sample when the molecules come either from within or from the other side. We show first results obtained with our apparatus, discuss the design of an instrument now under construction with ≈1-μm resolution, and describe briefly some more advanced versions under consideration with ≈100-Å resolution.
Particles with RNA of High Molecular Weight and RNA-Directed DNA Polymerase in Human Brain Tumors
Authors: Cuatico W. , Cho J.-R. , Spiegelman S.
Published: May 2006

We have previously shown that neoplastic cells of human breast cancers, leukemias, lymphomas, and sarcomas contain particles similar to the viruses that have been established as etiologic agents of these diseases in mice. The present paper concerns tumors of the central nervous system for which no suitable animal model or corresponding virus exists. Nevertheless, using the simultaneous detection test, we showed that human brain tumors contain 70S RNA and RNA-directed DNA polymerase encapsulated in a particulate component possessing a density of 1.17 g/ml. These particles satisfy the three diagnostic criteria that characterize RNA tumor viruses of animals. 24 Out of 26 (92%) of the most malignant (glioblastoma and medulloblastoma) brain tumors examined contained these virus-like entities.
Strychnine Binding Associated with Glycine Receptors of the Central Nervous System
Authors: Young Anne B. , Snyder Solomon H.
Published: May 2006

[
3
H]Strychnine binds to synaptic-membrane fractions of the spinal cord in a selective fashion, indicating an interaction with postsynaptic glycine receptors. Displacement of strychnine by glycine and other amino acids parallels their glycine-like neurophysiologic activity. The regional localization of strychnine binding in the central nervous system correlates closely with endogenous glycine concentrations. In subcellular fractionation experiments, strychnine binding is most enhanced in synaptic-membrane fractions. Strychnine binding is saturable, with affinity constants for glycine and strychnine of 10 and 0.03 μM, respectively.
Functions of a New Photoreceptor Membrane
Authors: Oesterhelt Dieter , Stoeckenius Walther
Published: May 2006

The purple membrane of
Halobacterium halobium
contains only one protein, bacteriorhodopsin, which closely resembles the visual pigments of animals. Light flashes cause a rapid transient shift of its absorption maximum from 560 to 415 nm. This shift is accompanied by release and uptake of protons. Respiring cells acidify the medium in the dark; if they contain purple membrane their O
2
consumption is reduced in the light. Starved or anaerobic cells containing purple membrane, in the absence of any apparent source of energy, generate and maintain a proton gradient across the cell membrane as long as they are exposed to light. We postulate that the light-generated proton gradient arises from a vectorial release and uptake of protons by bacteriorhodopsin, which is suitably oriented in the cell membrane and under continuous illumination oscillates rapidly between the long- and short-wavelength form. Preliminary results indicate that the gradient in
H. halobium
plays the central role in energy coupling attributed to such electrochemical gradients by Mitchell's chemiosmotic theory.