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Biomedical subjects

K Nishio

Publications and source records attributed to K Nishio.

At least 253 records · Page 14Linked to original sources
PubMed1982

Interaction of aminoacyl-tRNA with bacterial elongation factor Tu: GTP complex: effects of the amino group of amino acid esterified to tRNA, the amino acid side chain, and tRNA structure.

The present investigation was undertaken to see to what extent the alpha-amino group of the amino acid, the side chain of the amino acid of aminoacyl-tRNA, and the tRNA structure are involved in determining the affinity of aminoacyl-tRNA for bacterial elongation factor Tu-GTP complex. Various aminoacyl-tRNAs, mis-aminoacylated tRNAs, and formylated aminoacyl-tRNAs were prepared, and the dissociation constants of the ternary complexes of aminoacyl-tRNA with ET-Tu: GTP were determined by the RNase-resistance assay. The results indicated that the free amino-acid group of the amino acids in aminoacyl-tRNA is strongly required for binding with EF-Tu : GTP. In this concentration, the biological significance of formylation for Met-tRNAMetf species is discussed.

Amino Acids↗
PubMed1982

Isolation and characterization of a Pseudomonas aeruginosa PAO mutant defective in the structural gene for the LIVAT-binding protein.

A mutant of Pseudomonas aeruginosa PAO which has a defect in the structural gene for a binding protein for leucine, isoleucine, valine, alanine, and threonine (LIVAT-binding protein) was isolated and characterized. DL-4-azaleucine was taken up via the high-affinity branched-chain amino acid transport system (LIV-I), but not via the low affinity system (LIV-II), and then inhibited the growth of P. aeruginosa cells. This finding enabled us to select mutants defective in the LIV-I transport system alone. Among such mutants, strain PAO3530 was found to produce an altered LIVAT-binding protein. The shock fluid of this strain contained a normal level of the protein which corresponded to the wild-type LIVAT-binding protein as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by an immunological test. However, the shock fluid showed almost no binding activity for branched-chain amino acids, suggesting that strain PAO3530 has a defect in the structural gene for the LIVAT-binding protein. The mutation locus (bra-310) was mapped in a region between cnu-9001 and oru-325 on the chromosome of P. aeruginosa PAO by conjugation mediated by plasmid FP5 or R68.45.

Alanine↗
PubMed1980

Abnormal codon recognition of glycyl-tRNA from the posterior silk glands of Bombyx mori.

Two species of glycine tRNA (tRNA1Gly and tRNA2Gly) were purified from the posterior silk glands of Bombyx mori. Digestion of tRNA1Gly wit RNase T1 revealed that this tRNA corresponds to the species which has recently been sequenced by Garel and Keith (1), and Züniga and Steitz (2), independently. However, the position 9 of our tRNA2Gly was occupied by unmodified guanosine instead of m1G. The codon recognition properties of highly purified tRNA1Gly and tRNA2Gly were investigated in detail according to the method of Nirenberg and Leder (3). All four glycine codons were recognized by tRNA1Gly and by tRNA2Gly. These results suggest the presence of abnormal base-pairs between the first base G of the anticodon and all the third bases of the codons, or the recognition by "two-out-of-three" type reading.

Animals↗
PubMed1980

The interaction between the effects of insulin and ouabain on the activity of Na transport system in frog skeletal muscle.

The effects of insulin and ouabain on 22Na efflux and net Na loss were examined in frog sartorius muscles. After removal of ouabain, 22Na efflux which had been inhibited by ouabain remained at the inhibited level for more than 2 hr. In ouabain-free solution, insulin stimulated the Na efflux from ouabain-preincubated muscles. The stimulating effect of insulin on 22Na efflux was completely blocked by the presence of ouabain. Insulin shifted the Na efflux vs. intracellular Na concentration relationship toward the region of lower Na concentrations, and made the slope of log (Na efflux) vs. log [Na]1 relationship less step. On the other hand, ouabain shifted the Na efflux vs. intracellular Na concentration relationship toward the region of higher Na concentration, and made the slope of the log (Na efflux) vs. log [Na]1 relationship steeper. The relationship between insulin-stimulated Na efflux and intracellular Na concentration obtained from ouabain-preincubated muscle was located in the region of higher Na concentrations than that obtained from control muscle. These findings suggest that insulin increases an apparent affinity of binding sites for Na ions, and the possibility that insulin increases the Vmax of Na transport system may be excluded. In contrast with the effect of insulin, ouabain may be considered to decrease the apparent affinity of binding site for Na ions.

Animals↗
PubMed1980

Effects of ouabain on Na efflux in high internal Na and insulin-preincubated muscles.

To gain an insight into the mechanism of stimulation by insulin of Na efflux, the effect of high concentrations of internal Na on the inhibition by ouabain of Na efflux was compared to the inhibition by ouabain of insulin-stimulated Na efflux. The rate coefficient of 22Na efflux from "high-Na" muscle exposed to ouabain was lower than that from "low-Na" muscle exposed to ouabain. Similarly, the rate of net Na loss from the "high-Na" muscle which had been exposed to ouabain was lower than that frm the "low-Na" muscle. These findings indicate that Na transport units whose internal Na-binding sites have been occupied by Na is susceptible to ouabain. The insulin-stimulated Na efflux was inhibited by ouabain to a larger extent than was the Na efflux from the control muscle, although the final level of the rate coefficient of 22Na efflux from the muscle exposed to both insulin and ouabain was not always lower than that from the muscle exposed only to ouabain. The similarity between the effects of ouabain in "high-Na" muscle and in insulin-preincubated muscle suggests that insulin increases the fraction of Na transport units whose internal Na-binding sites have been occupied by Na.

Animals↗
PubMed1980

Apparent affinity changes induced by insulin of Na-K transport system in frog skeletal muscle.

The dependency of Na efflux on intracellular Na concentration was examined on sartorius muscles of Rana catesbeiana. In normal Ringer, the rate coefficient of 22Na efflux is nearly proportional to the internal Na concentration, i.e., Hill's coefficient in the dependency of Na efflux on internal Na concentration was around two. As long as insulin is present in the bathing solution, the rate coefficient of 22Na efflux retains the stimulated level. Insulin caused a leftward shift of the relationship between Na efflux and the logarithm of internal Na concentration, and concomitantly decreased Hill's coefficient. A model of the coupling of Na transport and hydrolysis of ATP was proposed. The theoretical relation derived from this model accounted for these findings quite satisfactorily. According to this model, insulin shifts as a cofactor the equilibrium between dephosphorylated and phosphorylated states of carriers, whose Na binding sites are not occupied by Na, toward the phosphorylated state.

Animals↗