Experimental studies on the effects of tension on intraneural microcirculation in sutured peripheral nerves.

Tension on an end-to-end nerve suture causes injury to the intraneural vessels. Impairment of the transverse anastomoses occurs first, followed by degeneration of the intrafascicular vessels. The the transverse anastomoses undergo complete degeneration, and the extrafascicular vessels also sustain severe damage. This series of circulatory disturbances is an important factor to consider when determining the advisability of an end-to-end nerve suture.     

Relation of solute and sorbed boron to the boron hazard in irrigation water

Summary The current criteria for evaluating the boron (B) hazard of irrigation water for specified crops are based on the concentration of B in the irrigation water without consideration of soil properties or the leaching fraction. Experiments were conducted to determine the influence of B sorption capacity on plant uptake of B at rates of 0.1, 2.5, 5.0 and 10.0 ppm B in the irrigation water with a leaching fraction of 0.5. A relatively B sensitive crop, oats (Avena sativa), was grown on four arid-region soils of varying B sorption capacities. The results show that B in solution rather than sorbed B influenced B toxicity. Contribution from the Department of Soils, Water and Engineering, The University of Arizona, Tucson, Arizona 85721. Arizona Agricultural Experiment Station No. 2508. Research Associates and Associate Professor, respectively. The senior author is currently at the Department of Soils and Irrigation, American University of Beirut Beirut, Lebanon.     

Negatively charged RNase-susceptible molecules on the surface of ascites tumor cells

RNase-susceptible ionogenic groups on the cell surface membranes of two leukemic and two nonleukemic strains of ascites tumor cells were studied by cell electrophoresis, DEAE-Sephadex A-25 column and paper chromatography, and indirect membrane immunofluorescence. RNase treatment of the nonleukemic ascites tumor cells (Ehrlich ascites tumor and Sarcoma 180) produced a significant reduction in their electrophoretic mobilities. When the cells were labeled with [3H]uridine then incubated with RNase, there was a marked increased in the radioactive nucleotides present in the incubation medium as compared to the results of the experiment with RNase-untreated controls. Indirect membrane immunofluorescence studies of nonleukemic ascites tumor cells suggest that the sites that react with anti-RNA antibody are distributed diffusely on their surfaces. RNase treatment of these cells markedly reduced their ability to react with the antibody. It thus appears that RNAs are present on the surface membrane of nonleukemic ascites tumor cells and that RNase digests these RNAs, removing negatively charged nucleotides from their electrophoretic surfaces. This results in a reduction in mobility. In contrast, leukemic ascites cells (L1210 and C1498) incubated with RNase showed no significant change in mobility or in the amount of nucleotides released into the incubation medium. Moreover, no fluorescence was found on the surface of cells examined by indirect membrane immunofluorescence. This suggests that leukemic ascites cells are devoid of RNAs on their surface.     

Demonstration of a high affinity Ca2+ ATPase in rat liver plasma membranes

Rat liver plasma membranes contained a high affinity Ca²⁺-ATPase which had an apparent half saturation constant of 0.2 μM for calcium. The Ca²⁺-ATPase was not stimulated by adding magnesium and/or calmodulin. Conversely, the addition of these substances diminished the calcium-stimulation of the ATPase. Orthovanadate (7 nM-2 mM), mitochondrial ATPase blockers (NaN₃, KCN, dicyclohexylcarbodiimide), Na⁺, K⁺ and ouabain had no effect on the ATPase activity. The ATPase was separated from nonspecific divalent cation stimulatable ATPase (Mg²⁺-ATPase) by solubilization with Triton X-100 followed by a Sephadex G-200 column chromatography and showed an apparent molecular weight of 200,000.     

β-structure from the microfibillar proteins of Merino wool

The β-structure of S-caboxymethyl derivatives of microfibrillar proteins isolated from Merino wool was investigated by X-ray diffraction for comparison with the structur of β-keratin. The S-carboxymethylated microfibrillar proteins(SCMKA) w well-oriented β-films of SCMKA weer obtained by stretching the SCMKA cast films in steam up to about 300% extesnsion. It was found that the reflections in β-pattern of SCMKA may be indexed on a pseudo-orthorhombic unit cell with a =0.94 nm, b = 0.66 nm and c = nm, where the ab, and c axes are in the direction of the interchain hydrogen bonding, the main chain(fibre axis) and the side chain, respectively. The unit cell dimesnions evaluated for SCMKA were almost the same as those for β-keratin, suggeting that few peptide sequences containing S-carboxymethyl cystine may be involved in the formation of β-structure from SCMKA.     

Isolation and characterization of visible light-sensitive mutants of Escherichia coli K12

Six mutants of Escherichia coli K12 that are sensitive to visible light have been isolated. Five of them, including an amber mutant, are defective in a gene that maps near 11 minutes on the linkage map of the chromosome, and this gene has been designated visA. The sixth mutant, which was isolated from bacteria that carried the visA+/visA+ diploid allele, is defective in a gene that maps near 63 minutes on the linkage map, which has been designated visB. These mutant strains of bacteria are killed by illumination with visible light. The effective wavelength of the light is around 460 nm. The nucleotide sequence of the visA gene was determined. As a result of a search for homologous products, we found that visA may be identical to hemH, the structural gene for ferrochelatase which catalyzes a final step in the biosynthesis of heme. A possible mechanism for the killing of the visA mutant bacteria is discussed.     

Characterization of the phosphatase activity of a baculovirus-expressed calcineurin A isoform.

Calcineurin A was purified by calmodulin-Sepharose affinity chromatography from Sf9 cells infected with recombinant baculovirus containing the cDNA of a rat calcineurin A isoform. The Sf9-expressed calcineurin A has a low basal phosphatase activity in the presence of EDTA (0.9 nmol/min/mg) which is stimulated 3-5-fold by Mn2+. Calmodulin increased the Mn2+ stimulated activity 3-5-fold. Bovine brain calcineurin B increased the A subunit activity 10-15-fold, and calmodulin further stimulated the activity of reconstituted A and B subunits 10-15-fold (644 nmol/min/mg). The Km of calcineurin A for 32P-RII pep (a peptide substrate (DLDVPIPGRFDRRVSVAAE) for CaN), was 111 microM with or without calmodulin, and calmodulin increased the Vmax about 4-fold. The Km of reconstituted calcineurin A plus B for 32P-RII pep was 20 microM, and calmodulin increased the Vmax 18-fold without affecting the Km. CaN A467-492, a synthetic autoinhibitory peptide (ITSFEEAKGLDRINERMPPRRDAMP) from calcineurin, inhibited the Mn2+/calmodulin-stimulated activities of the reconstituted enzyme and the A subunit with IC50's of 25 microM and 90 microM, respectively. The reconstitution of the phosphatase activity of an expressed isoform of calcineurin A by purified B subunit and calmodulin may facilitate comparative studies of the regulation of calcineurin A activity by the B subunit and calmodulin.     

A DBL-homologous region of the yeast CLS4/CDC24 gene product is important for Ca(2+)-modulated bud assembly.

The CLS4/CDC24 is essential for the budding process of the yeast Saccharomyces cerevisiae. Disruption of the CLS4/CDC24 gene is lethal, and expression of the CLS4 product under the control of the GAL1 promoter is sufficient for cellular growth. The CLS4 product is detected in yeast cell lysate with an apparent molecular mass of 93 kD (854 amino acid residues) and shows homology with the human DBL oncogene product. Temperature-sensitive cdc24-1 mutation is located in the N-terminal portion of the protein whereas Ca(2+)-sensitive cls4-1 mutation is present after the DBL-homologous region (amino acid residues 281-518) near the putative Ca(2+)-binding site. Mutations within the DBL-homologous region are responsible for the Ca(2+)-sensitive phenotype. Thus the CLS4 gene product seems to have several functional domains within the molecule essential for bud assembly.     

Primate's p53 inhibits SV40 DNA replication in vitro

Previous reports indicated that rodent p53 inhibits simian virus 40 (SV40) DNA replication in vitro as well as in vivo while that from primate cells does not (1-4). Here we report the evidence that p53 of primate origin also inhibits SV40 DNA replication in vitro. p53-SV40 large tumor antigen (T antigen) complex purified from SV40 infected COS-1 cells had little replication activity and inhibited SV40 DNA replication in vitro. These results suggest that inhibition of SV40 DNA replication by p53 should be regarded as general property of the protein and does not determine the mode of species specific replication of SV40 DNA.     

Elastic behavior of zymogen granule membranes in response to changes in pH and pCa.

In the process of secretion, the membrane of secretory granules is expected to change its elastic behavior. Elastic modulus of the membrane of zymogen granules, prepared from the rat pancreas acinar cell, was measured by an osmotic swelling method. The elastic modulus of the granule membrane at pCa 8 reduced from the maximal value of 230 dyn/cm at pH 6.0 to almost zero at pH 7.5. In a cytosol of an acinar cell, calcium ions play an important role as a second messenger in secretion. The elastic modulus of the granule membrane reduced in a sigmoidal fashion at pCa between 7.0 and 6.0. This range of pCa corresponds to a physiological rise of free Ca2+ concentrations in the cell cytosol when stimulated by external secretagogues. Reduction of the elastic modulus indicates that the state of the granule membrane switches to a more flexible one in which the granule is easy to appose to the cell plasma membrane and then swell as a final step of exocytosis.