bluuebunny/crossref_metadata_2025 huggingface dataset:
Approximate steady-state properties of lattices of interacting three-state enzyme molecules: a novel phase transition.
Authors: Hill T L , Stein L
Published: May 2006

Previous work on the cooperative behavior of lattices of interacting two-state enzyme molecules at steady state is extended here to interacting three-state enzyme molecules with a one-way cycle. The Bragg-Williams (mean field) approximation is used. A phase-transition example with a bifurcation point is discussed. Compared to conventional phase transitions (with a van der Waals loop), several new and complicated features appear. A second paper on this subject will contain a number of other examples of three-state systems.
H
p

theory for the poly-disc
Authors: Gundy R. F. , Stein E. M.
Published: May 2006

We show that the

H
p

spaces on the bi-disc can be characterized in terms of either the nontangential maximal function and the area integral or their probabilistic analogues resulting by introducing two-time Brownian motion (i.e., the martingale maximal function) and the corresponding square function.
Identification and isolation of a collagen-binding fragment of the adhesive glycoprotein fibronectin.
Authors: Hahn L H , Yamada K M
Published: May 2006

We have identified and purified a polypeptide region containing the collagen-binding site of the adhesive glycoprotein fibronectin. Chicken cellular fibronectin isolated from cultured embryonic fibroblasts was permitted to bind to gelatin coupled to agarose beads and was then digested extensively with chymotrypsin. A prominent 40,000-dalton fragment of fibronectin consisting of a single polypeptide chain was detected by sodium dodecyl sulfate/polyacrylamide gel electrophoresis of material remaining bound to the gelatin-agarose. This fragment appeared within 10 min after the digestion was initiated and persisted for more than 20 hr. This proteolytic fragment was isolated in electrophoretically pure form and retained its affinity for collagen. Plasma fibronectins from chicken and human blood also contained collagen-binding proteolytic fragments of similar size. This finding suggest that the collagen-binding sites of cellular and plasma fibronectins are homologous.
Soluble precursor of an integral membrane protein: synthesis of procoat protein in Escherichia coli infected with bacteriophage M13.
Authors: Ito K , Mandel G , Wickner W
Published: May 2006

Prior to virus assembly, the major coat protein of coliphage M13 is an integral protein of the host cytoplasmic membrane. Coat protein synthesized in vitro is initially made with an NH2-terminal "leader peptide" of 23 amino acids and is termed "procoat." We now report that procoat is a biosynthetic precursor of coat protein in vivo. Conversion of procoat to coat occurs within 30 sec in cells infected with wild-type virus. This proteolytic processing is delayed in cells infected by M13 mutants (in genes 1, 5, or 7) that are defective in virus assembly. Pulse--chase experiments in combination with subcellular fractionation show that procoat is synthesized in a soluble form in the cytoplasm and is then incorporated into the cytoplasmic membrane, where it is converted to coat protein. This finding is supported by the observation that procoat is synthesized exclusively by polysomes that are not membrane bound. These results are interpreted in terms of the "membrane-triggered folding" hypothesis of membrane protein assembly.
Lateral translational diffusion of cytochrome
c
oxidase in the mitochondrial energy-transducing membrane
Authors: Höchli Matthias , Hackenbrock Charles R.
Published: May 2006

The degree of freedom for lateral translational diffusion by cytochrome
c
oxidase and other integral proteins in the energy-transducing membrane of the mitochondrion was determined by combining the use of an immunoglobulin probe monospecific for the oxidase with thermotropic lipid phase transitions. Lateral mobility of the oxidase was monitored by observing the distribution of the immunoglobulin probe on the membrane surface by deep-etch electron microscopy and by observing the distribution of intramembrane particles (integral proteins) in the hydrophobic interior of the membrane by freeze-fracture electron microscopy. Incubation of the membrane with the immunoglobulin resulted in a time-dependent clustering of predominantly large intramembrane particles. Low temperature-induced lipid phase transitions resulted in the close packing of all intramembrane particles and cytochrome
c
oxidase by lateral exclusion from domains of gel-state bilayer lipid and was completely reversible. However, when cytochrome
c
oxidase was crosslinked through an immunoglobulin lattice prior to returning the membrane to above the lipid phase transition temperature, small intramembrane particles rerandomized while the large oxidase-related particles remained clustered. These observations reveal that cytochrome
c
oxidase can diffuse laterally in the energy-transducing membrane, either independently of all other integral proteins or in physical union with one or more other integral proteins. In addition, many other as yet unidentified smaller integral proteins can diffuse independently of the oxidase.
Dual control of cell growth by somatomedins and platelet-derived growth factor.
Authors: Stiles C D , Capone G T , Scher C D , Antoniades H N , Van Wyk J J , Pledger W J
Published: May 2006

Quiescent BALB/c 3T3 cells exposed briefly to a platelet-derived growth factor (PDGF) become "competent" to replicate their DNA but do not "progress" into S phase unless incubated with growth factors contained in platelet-poor plasma. Plasma from hypophysectomized rats is deficient in progression activity; it does not stimulate PDGF-treated competent cells to synthesize DNA, demonstrating that somatomedin C is required for progression. Various growth factors were tested for progression activity and competence activity by using BALB/c 3T3 tissue culture assays. Multiplication stimulating activity and other members of the somatomedin family of growth factors are (like somatomedin C) potent mediators of progression. Other mitogenic agents, such as fibroblast growth factor, are (like PDGF) potent inducers of competence. Growth factors with potent progression activity have little or no competence activity and vice versa. In contrast, simian virus 40 provides both competence and progression activity. Coordinate control of BALB/c 3T3 cell growth in vitro by competence factors and somatomedins may be a specific example of a common pattern of growth regulation in animal tissues.
Fetal cells in the blood of pregnant women: detection and enrichment by fluorescence-activated cell sorting.
Authors: Herzenberg L A , Bianchi D W , Schröder J , Cann H M , Iverson G M
Published: May 2006

Fetal cells, potentially usable for prenatal diagnosis, were sorted from maternal blood samples taken as early as 15 weeks of gestation. Immunogenetic and cytogenic criteria established the fetal origin of the observed cells: Y-chromatin-containing (male) cells were detected in the sorted sample if and only if the newborn proved to be male and carried cell-surface antigens detected by the fluorescent-labeled antibody used for sorting with the fluorescence-activated cell sorter.
Biochemical determinants of tumor sensitivity to 5-fluorouracil: Ultrasensitive methods for the determination of 5-fluoro-2′-deoxyuridylate, 2′-deoxyuridylate, and thymidylate synthetase
Authors: Moran Richard G. , Spears C. Paul , Heidelberger Charles
Published: May 2006

Techniques have been developed to measure FdUMP, the active metabolite of 5-FUra; thymidylate synthetase (TMP synthase; 5,10-methylenetetrahydrofolate:dUMP
C
-methyltransferase, EC 2.1.1.45), the target enzyme for this antimetabolite; and dUMP, the substrate that competes with FdUMP for binding to TMP synthetase. As little as 0.02 pmol of FdUMP can be quantitated with a competitive ligand binding assay by using homogeneous
Lactobacillus casei
/MTX TMP synthetase as a binding protein. A new binding assay for TMP synthetase allows detection of 0.005 pmol of enzyme. The quantitative enzymatic conversion of dUMP to [
methyl
-
14
C]-TMP using 5,10-methylene[
14
C]tetrahydrofolate by pure
L. casei
TMP synthetase is used as an assay for dUMP with a sensitivity of 10 pmol.

Cultured CCRF-CEM human lymphoblastic leukemia cells formed high levels of FdUMP (2.6 nmol per 10
9
cells) within 11 hr after exposure to 30 μM 5-FUra. Tumor cell TMP synthetase levels dropped, and then free FdUMP appeared. The intracellular dUMP pool was low (2-5 nmol per 10
9
cells) in logarithmically growing cultures of several tumor cell lines but expanded rapidly in CCRF-CEM cells on exposure to 5-FUra after enzyme levels decreased. The levels of dUMP found after exposure to 5-FUra are sufficient to severely retard inhibition of TMP synthetase by FdUMP.

The methods described are sufficiently sensitive to allow these biochemical parameters of 5-FUra action to be measured in cell culture or in needle biopsy samples of human tumors.
Evidence for internal homology in bovine preproparathyroid hormone.
Authors: Cohn D V , Smardo F L , Morrissey J J
Published: May 2006

By means of a statistical method for detecting distant evolutionary relationships between proteins, we found a high probability that internal homologies exist in preproparathyroid hormone, the biological precursor of proparathyroid hormone and parathyroid hormone. The regions so defined were -27 to +22 of preproparathyroid hormone vs. +26 to +74 parathyroid hormone and -23 to +29 of preproparathyroid hormone vs. +30 to +81 of parathyroid hormone. Examination of these regions for possible similarities of internal secondary structure (beta turns, alpha helix, and beta sheet) by a second type of predictive formulation indicated that most of the regions calculated to be related on an evolutionary basis were likewise homologous in terms of structure. These results and other considerations suggest that a primitive form of parathyroid hormone, possibly of pituitary origin, existed (or still exists). Parathyroid hormone of higher species likely was formed by gene doubling and fusion of the primitive gene.
Retrograde transport of nerve growth factor in chicken embryo.
Authors: Brunso-Bechtold J K , Hamburger V
Published: May 2006

We have demonstrated retrograde transport of nerve growth factor to the dorsal root ganglia in the chicken embryo. Polyacrylamide gel pellets impregnated with 125I-labeled nerve growth factor were implanted subcutaneously in the leg of stage 36 (10-day) chicken embryos. The embryos were killed 8 hr after implantation and were processed for routine autoradiography. Examination revealed significant labeling of all lumbar dorsal root ganglia on the side of the implanted pellet. The lateral motor columns and ventral roots as well as the dorsal roots on both sides were unlabeled. These observations show that in the chicken embryo, during the period of sensory cell sensitivity to nerve growth factor, there is a selective uptake and retrograde transport of nerve growth factor from the target area to the dorsal root ganglia. These observations supplement reports from other laboratories in which selective retrograde transport of nerve growth factor in neonatal and adult rodents has been demonstrated.
Stereocilia mediate transduction in vertebrate hair cells (auditory system/cilium/vestibular system).
Authors: Hudspeth A J , Jacobs R
Published: May 2006

The vertebrate hair cell is a sensory receptor that responds to mechanical stimulation of its hair bundle, which usually consists of numerous large microvilli (stereocilia) and a single true cilium (the kinocilium). We have examined the roles of these two components of the hair bundle by recording intracellularly from bullfrog saccular hair cells. Detachment of the kinocilium from the hair bundle and deflection of this cilium produces no receptor potentials. Mechanical stimulation of stereocilia, however, elicits responses of normal amplitude and sensitivity. Scanning electron microscopy confirms the assessments of ciliary position made during physiological recording. Stereocilia mediate the transduction process of the vertebrate hair cell, while the kinocilium may serve primarily as a linkage conveying mechanical displacements to the stereocilia.
Chemical crosslinking of a solubilized enkephalin macromolecular complex.
Authors: Zukin R S , Kream R M
Published: May 2006

Covalently bound [3H]D-Ala2,Met5-enkephalinamide- and 125I-labeled D-Ala2,N-Me-Phe4,Met-(O)5-ol-enkephalin-macromolecule complexes have been prepared by crosslinking the solubilized noncovalent complexes from rat brain. Gel electrophoresis of the partially purified 125I-labeled enkephalin-macromolecule complex under nondenaturing conditions results in a single major/radioactive peak. The complex has a Stokes radius of approximately 48 A as determined by molecular exclusion chromatography; this radius corresponds to a molecular weight of 380,000 for a spherical molecule. In preliminary experiments, sodium dodecyl sulfate electrophoresis of the complex shows a major radioactive peak corresponding to a molecular weight of 35,000. The preparation of these specific covalent enkephalin-macromolecule complexes should be useful in purification of the receptor and in probing the molecular mechanism of opiate action.
Inhibition of neuronal acetylcholine sensitivity by α-toxins from
Bungarus multicinctus
venom
Authors: Ravdin Peter M. , Berg Darwin K.
Published: May 2006

Bungarus multicinctus
venom contains several α-toxins in addition to the widely used α-bungarotoxin (Bgt 2.2). We have found that two of the α-toxins (Bgt 3.1 and 3.3) inhibit neuronal acetylcholine (AcCho) sensitivity when tested on ciliary ganglion neurons in cell culture. Over 90% of the AcCho sensitivity recorded in response to iontophoretic application of AcCho was blocked when the neurons were incubated with either of the toxins at 10
-7
M for 1 hr at 37°C. The blockade could be partially reversed by incubating the neurons for 1-2 hr in medium lacking the toxins. The neurons also had a high-affinity binding site for Bgt 2.2, as indicated by binding studies with rhodamine-labeled Bgt 2.2. Concentrations of Bgt 2.2(10
-7
M) that should be nearly adequate to saturate the high-affinity site, however, had no detectable effect on AcCho sensitivity of the neurons. Higher concentrations of Bgt 2.2(10
-5
M) produced a partial inhibition of AcCho sensitivity, suggesting either that the neurons had two classes of binding sites for Bgt 2.2 (with the low-affinity site affecting AcCho sensitivity) or that the preparation of Bgt 2.2 contained minor components (e.g., Bgt 3.1 or 3.3) that were responsible for the blockade. The mechanisms by which Bgt 3.1 and 3.3 inhibit neuronal AcCho sensitivity remain unknown. If they bind specifically to the AcCho receptor, they will be useful agents for studying the distribution and regulation of this membrane component.
On the spectral geometry of spaces with cone-like singularities
Authors: Cheeger Jeff
Published: May 2006

I describe an extension of a portion of the theory of the Laplace operator on compact riemannian manifolds to certain spaces with singularities. Although this approach can be extended to include quite general spaces, this paper will confine itself to the case of manifolds with cone-like singularities. These singularities are geometrically the simplest possible, but they already serve to illustrate new phenomena that are typical of the more general situation. Moreover, by inductive arguments, the study of simplicial complexes whose simplices have constant curvature and totally geodesic faces (e.g.,
p.l.
manifolds) can in large measure be reduced to the study of cone-like singularities.
Complex-analyticity of harmonic maps and strong rigidity of compact Kähler manifolds
Authors: Siu Yum-Tong
Published: May 2006

A harmonic map
f
between two compact Kähler manifolds is shown to be either holomorphic or conjugate holomorphic under a suitable negativity condition on the curvature of the image manifold and a condition on the rank of
df
. As a consequence, a compact Kähler manifold of dimension ≥2 that is of the same homotopy type as a compact Kähler manifold with suitable negative curvature condition or as a compact quotient of an irreducible classical bounded symmetric domain must be either biholomorphic or conjugate biholomorphic to it.
Further studies on the mode of action of the heme-controlled translational inhibitor: stimulating protein acts at level of binary complex formation.
Authors: de Haro C , Ochoa S
Published: May 2006

Previous work has shown that (i) at physiological concentrations of eukaryotic initiation factor 2 (eIF-2), formation of the ternary complex eIF-2-GTP-Met-tRNAi, which precedes the assembly of a 40S initiation complex, requires the presence of eIF-2 stimulating protein (ESP) and (ii) the interaction of eIF-2 with ESP is blocked by the translational inhibitor which, in reticulocyte lysates, is activated in the absence of hemin. Present evidence indicates that formation of the ternary complex is preceded by formation of the binary complex eIF-2-GTP and that ESP acts at the level of binary complex formation.
Initiation of general recombination catalyzed in vitro by the recA protein of Escherichia coli.
Authors: McEntee K , Weinstock G M , Lehman I R
Published: May 2006

Homogeneous recA protein catalyzes the hybridization of single-stranded DNA to homologous regions in duplex DNA. The products are D-loops, which are formed with equal efficiency in linear and supercoiled molecules. This assimilation reaction can be separated into two partial reactions. In the first, recA protein binds to duplex DNA and produces a reA protein-DNA complex. The binding shows a sigmoidal dependence on recA protein concentration, requires ATP, GTP or the gamma-thio analog of ATP, and Mg2+, but does not require hydrolysis of the nucleoside triphosphate. In the second reaction, single-stranded regions of the recA protein-ATP-duplex DNA intermediate hybridize with free complementary single strands to produce D-loop structures. This reaction is coupled to ATP hydrolysis and is analogous to the renaturation of single-stranded DNA catalyzed by the recA protein [Weinstrock, G.M., McEntee, K. & Lehman, I.R. (1979) Proc. Natl. Acad. Sci. USA 76, 126-130]. Hydrolysis of ATP appears to be required in these reactions for dissociation of recA protein from the DNA.
Ion-channel component of cytochrome oxidase.
Authors: Fry M , Green D E
Published: May 2006

Cytochrome oxidase is resolvable into an electron transfer complex and an ion transfer complex. The ion transfer complex has been shown to have the capability for inducing nonspecific ion transport into liposomes. Subunit I of cytochrome oxidase has been identified as an ion-channel-forming protein.
Insertion mutant of bacteriophage f1 sensitive to EcoRI.
Authors: Boeke J D , Vovis G F , Zinder N D
Published: May 2006

The nucleotide sequence A-A-T-T was inserted into the intergenic region of the f1 genome at a site cleaved by Hae III (cleavage sequence (G-G-C-C). The resultant viable phage mutant (R199) contains a single site sensitive to the restriction endonuclease EcoRI (cleavage sequence G-A-A-T-T-C). This phage is sensitive to EcoRI restriction and modification in vivo and in vitro. Its potential for use as a cloning vector has been tested by construction in vitro of an f1/pBR322 chimeric phage. The four bases inserted into wild-type f1 to generate the R199 mutant came from a small restriction fragment obtained by digesting plasmid pBR322 with EcoRI and HindIII. The use of this linker prepared from a biological substrate is an example of a technique for constructing restriction enzyme sites in vitro. It is presented as an alternative to the use of synthetic linkers and should be generally applicable.
Separation and structure of the prosthetic group of the blue fluorescence protein from the bioluminescent bacterium
Photobacterium phosphoreum
Authors: Koka Prasad , Lee John
Published: May 2006

The highly fluorescent prosthetic group of the blue fluorescence protein purified from the bioluminescent bacterium
Photobacterium phosphoreum
has been dissociated and separated from its apoprotein by affinity chromatography on Cibacron Blue-Sepharose. It has been identified as 6,7-dimethyl-8-(1′-D-ribityl)lumazine by several methods of characterization, all of which gave results identical to those for an authentic sample. In neutral solution, absorption maxima are at 407, 275 (shoulder), and 256 nm, with a single fluorescence maximum at 491 nm. The proton magnetic resonance spectrum exhibits a singlet at 2.66 ppm corresponding to the methyl substituted at the 6 position of lumazine and a multiplet centered at 3.85 ppm corresponding to the C-2′-5′ protons of the ribityl group. A Raman spectrum was obtained by the technique of coherent anti-Stokes Raman scattering and the

R
F

values by paper chromatography were determined in four solvent systems. The isolated compound was readily transformed into riboflavin by riboflavin synthetase. Fifty grams (dry weight) of
P. phosphoreum
contains at least 20 mg of this lumazine derivative, an amount comparable to that found in other microorganisms classified as riboflavin overproducers. The overproduction of this lumazine in this case apparently has to do with its function in the generation of bioluminescence.
Increased nuclease activity in cells treated with pppA2'p5'A2'p5' A.
Authors: Hovanessian A G , Wood J , Meurs E , Montagnier L
Published: May 2006

A series of 2'-5'-linked oligo(adenylic acid) triphosphate (2'-5' A) inhibitors of protein synthesis were described recently. These inhibitors are synthesized from ATP by an enzyme activated in interferon-treated cell extracts or rabbit reticulocyte lysates by double-stranded RNA. We show here that 2'-5' A is a potent inhibitor of protein synthesis in intact cells of different origin (human, monkey, hamster, and mouse). At a concentration of 10 nM (in AMP equivalents), protein synthesis is inhibited by 50-85%. There is also a secondary effect on the total RNA synthesis which becomes evident several hours after inhibition of protein synthesis. All of these effects, however, are transient and, after a recovery period, both RNA and protein synthesis resume rates comparable to the appropriate controls. A nuclease activity is detected in cells after treatment with 2'-5'A. The total polyadenylylated RNA is much reduced in comparison to that from untreated cells, and electrophoretic analysis in polyacrylamide slab gels provides evidence for its degradation. Similarly, there is an apparent degradation of ribosomal RNA. Consistent with these results, extracts from cells that had been treated with 2'-5'A manifest an enhanced nuclease activity in vitro on incubation with exogenous RNA. Here, we propose that, as in cell-free systems, the mechanism of action of 2'-5'A in intact cells involves activation of a nuclease. This activation is transient, but the nuclease remains sensitive to further activation by the inhibitor.
Water permeability changes studied by 17O nuclear magnetic resonance during differentiation of Friend leukemia cells.
Authors: Haran N , Malik Z , Lapidot A
Published: May 2006

Water permeability of Friend leukemia cells was studied by 17O nuclear magnetic resonance during differentiation induced by dimethyl sulfoxide (Me2SO). While in noninduced cells water permeability was essentially constant during the growth period, in the Me2SO-induced cells there were two distinct periods at which the water permeability was increased by at least an order of magnitude. These periods correspond to approximately one doubling time and 6 days of growth. This change in water permeability is not due to direct interaction of Me2SO with the membrane but must be ascribed to structural changes in the membrane during the course of differentiation.
Light-induced damage to ocular lens cation pump: prevention by vitamin C.
Authors: Varma S D , Kumar S , Richards R D
Published: May 2006

The cation pump activity of the ocular lens was damaged by exposure to light in the presence of riboflavin phosphate. The intensity of light was similar to that used for reading purposes. The observed light-induced damage was due to superoxide or its derivatives, the superoxide being produced photochemically. Such damage was attenuated by vitamin C in amounts comparable to that in the aqueous humor. Thus, a new role for the high ascorbate level present in the anterior chamber fluid and the lens has been suggested. Ascorbate in other tissues also might have this novel physiological function of protecting against damage due to superoxide and its derivatives produced during normal cellular oxidation.
Degradation of junctional and extrajunctional acetylcholine receptors by developing rat skeletal muscle.
Authors: Steinbach J H , Merlie J , Heinemann S , Bloch R
Published: May 2006

We have examined the rate of degradation of the total acetylcholine receptor content of diaphragm muscles of young rats and have found that even in muscles from 1-day-old rats some receptors are metabolically more stable than adult extrajunctional receptors. Further experiments have shown that acetylcholine receptors at junctional regions from young rats are degraded slowly, whereas those in extrajunctional regions are degraded rapidly. The results demonstrate that junctional acetylcholine receptors in rat diaphragm are degraded at a slow rate characteristic of adult junctional receptors at all ages after birth.
Immunocytochemical localization of rat peripheral nervous system myelin proteins: P2 protein is not a component of all peripheral nervous system myelin sheaths.
Authors: Trapp B D , McIntyre L J , Quarles R H , Sternberger N H , Webster H D
Published: May 2006

Specific antibodies have been developed against P1, P2, and P0 myelin proteins and were used to study the localization of these proteins in the rat peripheral nervous system. Both peripheral and central nervous system myelin sheaths contain P1 protein. P0 and P2 proteins are found exclusively in peripheral nervous system myelin sheaths. Antisera to P1 and P0 proteins stain all peripheral nervous system myelin sheaths uniformly. P2 protein is not a component of all peripheral nervous system myelin sheaths. In sheaths that do contain P2 protein, it is concentrated in the area of the Schmidt-Lanterman incisures.
Amino acid sequence and physicochemical similarities between streptococcal M protein and mammalian tropomyosin.
Authors: Hosein B , McCarty M , Fischetti V A
Published: May 2006

The amino-terminal sequences of two peptides of type 24 streptococcal M protein show similarities with that of rabbit skeletal muscle tropomyosin, having up to 40% identical residues and probabilities of occurring by chance as low as P less than 10(-5). In addition, a hexapeptide (Glu-Ala-Glu-Lys-Ala-Ala) that is found five times in the M24 protein was shown to be identical to a sequence in tropomyosin. Similarities are also seen in the amino acid compositions and physicochemical properties of the two proteins. The amino-terminal sequences of peptides from another bacterial surface protein, staphylococcal protein A, are highly correlated with segments of two other myofibrillar proteins, rabbit actin (P less than 10(-7)) and rabbit myosin A1 light chain (P less than 10(-6)). The data presented suggest that a close structural relationship exists between mammalian muscle proteins and the biologically active surface proteins of staphylococci and streptococci. In addition, the correlation between sequences in M protein and tropomyosin represents direct evidence of a structural similarity at a molecular level between a streptococcal protein and a mammalian muscle component and may therefore prove relevant to the pathogenicity of the streptococcus.
Allogeneic cytolysis of reconstituted membrane vesicles.
Authors: Hollander N , Mehdi S Q , Weissman I L , McConnell H M , Kriss J P
Published: May 2006

The successful use of lipid bilayer model membranes as targets for cytotoxic lymphocytes is described. Lipid vesicles were made from a mixture of dipalmitoyl lecithin, dimyristoyl lecithin, and cholesterol. Membrane proteins of LSTRA or EL4 tumor cells (as source of H-2 antigens), human eye muscle membrane proteins (as supporting proteins), and 51Cr marker were inserted into the lipid vesicles. Incubation of the reconstituted vesicles with lymphocytes sensitized in mixed lymphocyte cultures against allogeneic cells resulted in the specific release of intravesicular 51Cr. Vesicle damage was mediated by thymus-derived lymphocytes. H-2 antigens could be incorporated into vesicles without eye muscle proteins. However, immune damage of the vesicles could not be demonstrated when vesicles inserted with H-2 antigens in the absence of eye muscle proteins were used as targets.
Release of platelet-derived growth factor from human platelets by arachidonic acid
Authors: Linder Barbara L. , Chernoff Arthur , Kaplan Karen L. , Goodman DeWitt S.
Published: May 2006

Platelet α-granules contain a factor that stimulates the proliferation of arterial smooth muscle cells and may play a role in atherogenesis. We have studied the role of arachidonic acid in mediating the release of the platelet-derived growth factor (PDGF) from human platelets. PDGF was assayed by stimulating of [
3
H]thymidine incorporation into DNA of mouse 3T3 cells. Platelet aggregation and the release of platelet factor 4,β-thromboglobulin, and serotonin were also studied. A biphasic response pattern was observed when gel-filtered platelets were incubated with arachidonate over the concentration range 0.01-0.4 mM. At low arachidonate levels (approximately 0.025-0.1 mM), specific concentration-dependent aggregation and release of PDGF and of the other components were observed. This effect was not seen with any of five other fatty acids tested and was suppressed by indomethacin (25 μM). At higher arachidonate concentrations (approximately 0.15-0.35 mM), a concentration-dependent turn-off of both aggregation and release occurred. At these concentrations the platelets remained functional, and no release of lactate dehydrogenase was observed. A similar biphasic pattern of arachidonate-induced aggregation and release was observed with platelet-rich plasma, over a similar range of arachidonate to albumin mole ratios. These studies demonstrate that PDGF and other α-granule constituents can be released from platelets specifically by arachidonate via an indomethacin-sensitive pathway, most probably involving the platelet cyclooxygenase and conversion of arachidonate to prostaglandin metabolities. The mechanisms responsible for the turn-off of the specific arachidonate-mediated responses at higher arachidonate concentrations remain to be defined.
Earth resources
Authors: Skinner Brian J.
Published: May 2006

Reliable supplies of metals have historically been the keys to industrial and technological development. But many metals are subject to the possible exhaustion of traditional kinds of deposits. A continued supply of such metals, which include tin, tungsten, silver, lead, zinc, and many others, will require their recovery from common rocks, in which they are found in solid solution in common silicate minerals. Recovery from unconventional sources will be so energy intensive that we may eventually have to stop mining such metals. The greatest challenge facing the U.S. Geological Survey in its second century will be the problem of resource limitations.
Characterization of a histone-like protein extracted from yeast mitochondria.
Authors: Caron F , Jacq C , Rouvière-Yaniv J
Published: May 2006

Analysis of proteins isolated by affinity chromatography on DNA-cellulose from highly purified yeast mitochondria shows that these organelles do not contain histones but have in abundance a DNA-binding protein of 20,000 daltons. The purification yield of this protein, called HM, indicates that mitochondria have at least an equal mass of HM relative to DNA. The amino acid composition and its electrophoretic characterization reveal that HM, rich in lysine, is slightly basic and heat stable. HM appears to be coded by the yeast nucleus, as shown by its presence in several "petite" mutants. We have shown that HM, like histones or histone-like proteins, is able to introduce superhelical turns into circular relaxed DNA in the presence of a nicking-closing activity.
Characterization of alkylamine-sensitive site in alpha 2-macroglobulin.
Authors: Swenson R P , Howard J B
Published: May 2006

Methylamine reacts with the plasma protease inhibitor, alpha 2-macroglobulin, to form an irreversible, covalent modification. Quantitation of the reaction indicates 3.9 +/- (SD) 0.4 reactive sites per native tetrameric protein (Mr = 725,000) or one site per subunit. The reaction is selective and specific in that only 1 or 2 labeled peptides are observed on radioautography of peptide maps derived from [14C]methylamine-treated alpha 2-macroglobulin. A single chymotryptic peptide was isolated in 56% overall yield from the labeled protein. The peptide sequence by Edman degradation was found to be Gly-Cys-Gly-Glu-X-Asn-Met-(Val, Leu), in which X was the only radiolabeled phenylthiohydantoin derivative. Amino acid analysis and mass spectral analysis of the derivative suggests that X is gamma-glutamylmethylamide. Because glutamic acid and glutamine residues do not normally react with alkylamines, this work presents presumptive evidence for an alternative activated center in selected proteins.
Enzymatic identification of mannose 6-phosphate on the recognition marker for receptor-mediated pinocytosis of beta-glucuronidase by human fibroblasts.
Authors: Natowicz M R , Chi M M , Lowry O H , Sly W S
Published: May 2006

Human beta-glucuronidase (beta-D-glucuronide glucuronosohydrolase, EC 3.2.1.31), like many other glycoprotein lysosomal hydrolases, is subject to receptor-mediated endocytosis by fibroblasts. Prior work demonstrated charge heterogeneity in beta-glucuronidase and showed that high-uptake forms are more acidic than slowly internalized forms. Considerable indirect evidence implicated mannose 6-phosphate as an essential part of the recognition marker on high-uptake enzyme forms. Here we report the purification of beta-glucuronidase from human spleen and demonstrate enzymatically that mannose 6-phosphate is released on acid hydrolysis of pure enzyme varies directly with its susceptibility to pinocytosis by fibroblasts. Enzyme forms resolved by CM-Sephadex chromatography differed over an 18-fold range in uptake rate and in mannose 6-phosphate content. The most acidic forms had 4.4 mol of mannose 6-phosphate per mol of enzyme. The mannose 6-phosphate was released from the enzyme by treatment with endoglycosidase H with concomitant loss of susceptibility to adsorptive endocytosis. Thus, these studies provide direct evidence that mannose 6-phosphate is present on high-uptake enzyme forms, that it is present in the recognition marker for uptake, and that it is present on oligosaccharide that is released by endoglycosidase H.
Comparison of adult, embryonic, and dystrophic myosin heavy chains from chicken muscle by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and peptide mapping.
Authors: Rushbrook J I , Stracher A
Published: May 2006

Chicken myosin heavy chains from adult fast white muscle fibers (both normal and dystrophic), adult slow red fibers, and embryonic presumptive fast white fibers were compared by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and by peptide mapping. The heavy chain of slow red myosin migrated electrophoretically more slowly than the heavy chains of the other myosins and differed markedly from them in its peptide maps. The heavy chain of dystrophic fast white myosin was similar to its normal counterpart by peptide mapping but showed slight differences. The peptide map of the heavy chain of embryonic presumptive fast white myosin had the general features of that of the heavy chain of fast white, not slow red, fibers but contained definite differences from the former. The results are consistent with the existence of a separate gene for the heavy chain of embryonic presumptive fast white myosin.
Subunit structure of dihydrolipoyl transacetylase component of pyruvate dehydrogenase complex from
Escherichia coli
Authors: Bleile Dennis M. , Munk Peter , Oliver Robert M. , Reed Lester J.
Published: May 2006

Limited tryptic digestion of the pyruvate dehydrogenase complex of
Escherichia coli
or its dihydrolipoyl transacetylase core cleaves the trypsin-sensitive transacetylase subunits into two large fragments, A (lipoyl domain) and D (subunit binding domain). Release of fragments A from the complex does not significantly affect its sedimentation coefficient or its appearance in the electron microscope. Fragment A contains the lipoyl moieties (
3
H-labeled), is acidic with an apparent isoelectric point of about 4.0, has a
M
r
of 31,600 as determined by sedimentation equilibrium analysis, and has a swollen or extended structure (

f/f
o

= 1.78). Fragment A exhibits anomalous properties, probably due to its acidic nature. It is resistant to staining with Coomassie blue and it migrates on sodium dodecyl sulfate/polyacrylamide gels as if it had a
M
r
of 46,000-48,000. Further tryptic digestion converts fragment A into a lipoyl-containing fragment of
M
r
20,000 (fragment B) and eventually into an apparently stable product of estimated
M
r
about 10,000 (fragment C). Fragment D has a compact structure of
M
r
about 29,600 as determined by sedimentation equilibrium analysis in 6 M guanidinium chloride, and it possesses the intersubunit binding sites of the transacetylase, the binding sites for pyruvate dehydrogenase and dihydrolipoyl dehydrogenase, and the catalytic site for transacetylation. The assemblage of fragments D is responsible for the cube-like appearance of the transacetylase in the electron microscope. High-resolution electron micrographs of the transacetylase show fiber-like extensions, apparently corresponding to tryptic fragment A, surrounding the cube-like core.
Filament interaction in intact muscle fibers monitored by light scattering.
Authors: Katz G M , Mozo A , Reuben J P
Published: May 2006

Measurement of changes in optical properties of intact muscle fibers during contraction has proven to be difficult or, in some cases, impossible due to movement of the muscle relative to the incident beam. In this paper we describe a technique for immobilizing single fibers in clear gelatin, which permits measurement of light scattering signals undistorted by movement artifacts. We also describe the phase and amplitude relationship between changes in intensity of light scattering (at 90 degrees to incident beam) and tensions induced by electrically activating single fibers. With tensions that range up to 50% Po (Po = maximal tension measured by exposure of fibers to 200 mM K+), the maximal increase in light scattering is about 25% of that for resting fibers. The scattering increase precedes tension, and at low temperatures the interval between the two peaks can be 50--100 msec. We interpret these data on intact fibers, as we did our earlier data from studied on skinned fibers, as indicating that increases in light scattering power of muscle are primarily due to attachment of myosin cross-bridges to actin filaments.
Interspecies homology of nitrogenase genes.
Authors: Ruvkun G B , Ausubel F M
Published: May 2006

Cloned nitrogen fixation (nif) genes from Klebsiella pneumoniae hybridize to DNA from 19 out of 19 widely divergent nitrogen-fixing bacterial strains but do not hybridize to DNA from 10 different non-nitrogen-fixing species. K. pneumoniae nif DNA fragments that hybridize to DNA from other species contain part of the three structural genes that code for nitrogenase polypeptides. We have utilized this homology to clone an EcoRI restriction endonuclease fragment from Rhizobium meliloti that hybridizes to the K. pneumoniae nif structural genes. Some of the species whose DNA hybridizes with K. pneumoniae nif DNA have been postulated to have diverged from K. pneumoniae 3 x 10(9) years ago. Nitrogenase genes are the only known example of such highly conserved prokaryotic translated genes. Nitrogenase genes are either extraordinarily conserved in evolution or have been exchanged between different nitrogen-fixing species relatively recently in evolutionary time.
Photoaffinity labeling of rat androgen binding protein.
Authors: Taylor C A , Smith H E , Danzo B J
Published: May 2006

The photoinactivation and photoaffinity labeling of androgen binding sites present in cytosol prepared from intact sexually mature rat epididymides have been demonstrated by using unlabeled and [3H]-labeled 17 beta-hydroxy-4,6-androstadien-3-one. Both photoinactivation and photolabeling are dependent upon exposure to light. These processes are inhibited when photolysis is conducted in the presence of the photoinert compound 17 beta-hydroxy-5 alpha-androstan-3-one, suggesting that steroid-specific sites are involved in the reactions. The labeled steroid-specific product of photolysis is macromolecular with a molecular weight of 47,000 as determined by electrophoresis on polyacrylamide gels containing NaDodSO4, and proteinaceous because digestion of the cytosol with pronase before photolysis eliminates steroid-specific binding. After photolysis, the protein-steroid complex has the ability to withstand dissociation during electrophoresis under denaturing conditions, and unlabeled 17 beta-hydroxy-5 alpha-androstan-3-one fails to displace the label from the complex. Thus, the binding of [3H]17 beta-hydroxy-4,6-androstadien-3-one to the cytosolic protein is covalent. This steroid-specific product is identified as an androgen binding protein of testicular origin by its comigration with native androgen binding protein on nondenaturing polyacrylamide gels and by its molecular weight which is within the range reported for androgen binding protein subunits.
Supramolecular structure of stacked and unstacked regions of the photosynthetic membranes of
Prochloron
sp., a prokaryote
Authors: Giddings Thomas H. , Withers Nancy W. , Staehelin L. Andrew
Published: May 2006

Freeze-fracture replicas of the photosynthetic prokaryote
Prochloron
sp., collected at Coconut Island, Hawaii, show that the thylakoids are differentiated into stacked and unstacked regions much like the thylakoids of green algae and higher plants. On the exoplasmic (E) fracture face, the particle density is greater in stacked regions (≈3100 particles/μm
2
) than in unstacked regions (≈925 particles/μm
2
). On the complementary protoplasmic (P) fracture face, the particle density is lower in stacked regions (≈2265 particles/μm
2
than in unstacked regions (≈4980 particles/μm
2
). The histogram of the diameters of E face particles in unstacked regions shows a single broad peak centered at 80 Å. In stacked regions, four distinct peaks, at 75, 105, 130, and 160 Å, are observed. These size classes are virtually identical to those found on E faces of thylakoids of the green alga
Chlamydomonas
and of greening pea chloroplasts. In the latter systems, the different size classes of E face particles are believed to represent photosystem II units surrounded by variable amounts of chlorophyll a/b light-harvesting complex. We propose that the same interpretation applies to the thylakoids of
Prochloron
, which contain a similar chlorophyll a/b complex. Our results add to the evidence supporting the view of the chlorophyll a/b complex as both a light-harvesting complex and a membrane adhesion factor. The similarity of the architecture of the thylakoids of
Prochloron
to that of green algal and plant chloroplasts also provides additional evidence of an evolutionary relationship between
Prochloron
and the chloroplasts of green plants.
Nuclear and cytoplasmic genes controlling synthesis of variant mitochondrial polypeptides in male-sterile maize
Authors: Forde Brian G. , Leaver Christopher J.
Published: May 2006

The polypeptides synthesized
in vitro
by mitochondria isolated from etiolated maize shoots of a number of different nuclear and cytoplasmic genotypes have been compared by using polyacrylamide gel electrophoresis. We have previously shown that mitochondria from maize plants carrying the T or C forms of cytoplasmically inherited male sterility (
cms
-T and
cms
-C mitochondria) can be distinguished from each other and from the mitochondria of normal (N) plants by the synthesis of a single additional or variant polypeptide species. Using lines that carry the T cytoplasm, and that differ principally in the presence or absence of nuclear “restorer” alleles that suppress the male-sterile phenotype, we find that these nuclear genes specifically suppress synthesis of the 13,000
M
r
variant polypeptide. A 21,000
M
r
polypeptide that is synthesized by N mitochondria is not detectable among the translation products of
cms
-T mitochondria from either restored or nonrestored lines. Results obtained with a number of lines possessing dominant restorer alleles from different sources indicate that it is the restorer gene at the
Rf
1
locus that is primarily responsible for regulating synthesis of the 13,000
M
r
polypeptide. Mitochondria from lines with the S form of cytoplasmic male sterility (
cms
-S) were found to synthesize a group of minor polypeptides, ranging in molecular weight from 42,000 to 88,000, which were not detected in N,
cms
-T, or
cms
-C mitochondria. In the case of the S and C forms of male sterility no differences were found between the translation products of mitochondria from restored and nonrestored lines.
Coupling of active ion transport and aerobic respiratory rate in isolated renal tubules.
Authors: Balaban R S , Mandel L J , Soltoff S P , Storey J M
Published: May 2006

We report the results of studies in which the cytoplasmic coupling between Na+,K+-ATPase activity (presumably a measure of active transport) and the mitochondrial respiratory rate was investigated in a tubule suspension from the rabbit kidney cortex. Simultaneous measurements of the redox state of mitochondrial nicotinamide adenine dinucleotide (NAD) (performed fluorometrically), the cellular ATP and ADP concentrations, and the oxygen consumption rate (QO2) were made under conditions known to alter the Na+,K+-ATPase turnover. Ouabain (25 microM) caused: (i) a 54% inhibition of QO2, (ii) a net reduction of NAD, and (iii) a 30% increase in the ATP/ADP ratio. The addition of K+ (5 ?M) to K+-depleted tubules caused: (i) an initial 127% stimulation of QO2 followed by a new steady-state QO2 50% above control, (ii) an initial large oxidation of NAD followed by a new steady state more oxidized than the control level, and (iii) a 47% decrease in the cellular ATP/ADP ratio. These data indicate that the cellular ATP and ADP concentrations or the ATP/ADP ratio may be part of the coupling mechanism linking Na+,K+-ATPase turnover and the aerobic metabolic rate in kidney.
Model for regulation of the histidine operon of Salmonella.
Authors: Johnston H M , Barnes W M , Chumley F G , Bossi L , Roth J R
Published: May 2006

A model is proposed that accounts for regulation of the histidine operon by a mechanism involving alternative configuration of mRNA secondary structure (the alternative stem model). New evidence for the model includes sequence data on three regulatory mutations. The first (hisO1242) is a mutation that deletes sequences needed to form the attenuator mRNA stem and causes constitutive operon expression. The second mutation (hisO9654) is a His- ochre (UAA) mutation in the leader peptide gene; the existence of this mutation constitutes evidence that the leader peptide gene is translated. The third mutation (hisO9663) is remarkable. It neither generates a nonsense codon nor affects a translated sequence; yet, it is suppressible by amber suppressors. We believe this mutation causes a His- phenotype by interfering with mRNA secondary structure. The suppressibility of the mutation is probably due to disruption of the attenuator stem by ribosomes that read through the terminator codon of the leader peptide gene. This explanation is supported by the observation of derepression of a wild-type control region in the presence of an amber suppressor. Evidence is presented that hisT mutants (which lack pseudouridine in the anticodon arm of histidine tRNA) may cause derepression of the his operon by slowing protein synthesis in the leader peptide gene.