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Biomedical subjects

Y Nishimura

Publications and source records attributed to Y Nishimura.

At least 1,207 records · Page 67Linked to original sources
PubMed1979

Proton transfer kinetics in the lowest excited state of 1,N6-ethenoadenosine as revealed by fluorescence lifetime measurements.

Fluorescence lifetimes have been examined of 1, N6-ethenoadenosine (epsilon Ado), 1-methyl-ethenoadenosine (m1 epsilon Ado+), 9-methyl-ethenoadenosine (m9 epsilon Ado+), N1-deazaethenoadenosine (N1-deaza-epsilon Ado, and 9-methyl-N1-deazaethenoadenosine (m9N1-deaza epsilon Ado) at various pH's in the 7.5 approximately 1.5 region and at 20 degrees C. From an analysis we have reached the following conclusions. (1) The observed fluorescence of epsilon Ado is caused by the unprotonated, neutral, excited species epsilon Ado not not only at pH 7 but also at pH 2. (2) pKa of the excited epsilon Ado is lower than that of the ground state epsilon Ado. (3) The rate constant of protonation in the excited state is about 10(10) sec-1 M-1.

Adenosine↗
PubMed1978

Murein-lipoprotein of Escherichia coli: a protein involved in the stabilization of bacterial cell envelope.

Two independent mutants of Escherichia coli lacking murein-lipoprotein have been found. One mutant whose mutation was named lpo was subjected to detailed analyses. The absence of both bound and unbound lipoproteins was shown by electrophoretic analysis of 14C-arginine labelled membrane proteins of the mutant. Nor was serologically cross-reacting material detected in the mutant by the Ouchterlony-method. Sequestering magnesium from mutant cell suspensions by ethylenediaminetetraacetic acid caused cell lysis, which was prevented in the presence of 0.5 M sucrose. Incubation in culture media at a very low level of magnesium resulted in the formation of blebs in the mutant. Examination of mutant cells by electron microscopy showed that the outer membrane of the mutant was uneven with small irregular protuberances, some of which pinched off forming vesicles of various sizes. Phosphotungstate used for negative-staining penetrated into the periplasmic space of the mutant cells. The mutants leaked a considerable fraction of their periplasmic enzymes. These physiological and morphological alterations in the lipoproteinless mutant suggest that murein-lipoprotein helps to maintain the outer envelope structure by connecting the outer membrane with murein so that the outer membrane may fulfil its physiological functions as a barrier to the environment.

Electrophoresis↗
PubMed1978

On the process of cellular division in Escherichia coli: a series of mutants of E. coli altered in the penicillin-binding proteins.

A series of mutants defective in penicillin-binding components (or protein) (PBCs) was isolated from a collection of thermosensitive mutants of Escherichia coli. The mutants included mutations for each PBC (1 through 4) and a mutation in the activity of D-alanine carboxypeptidase 1a (PBC-5/6). PBC-1 was resolved into two components, PBC-1a and PBC-1b, which were the products of different genes referred to as ponA and ponB, respectively. No mutation examined in ponA-- or ponB--, by itself, was associated with a thermosensitive defect in growth. The mutants having ponB-- were hypersensitive to cephalosporins, which showed unusually high affinity to PBC-1a. Murein synthetic activity decreased markedly in cell-free preparations from the ponB-- mutant. The double mutation ponA-- ponB-- was found to be lethal. A mutant having ponAts and ponB-- revealed thermosensitivity of growth and lysed at the restrictive temperature. It is concluded that PBC-1a and PBC-1b could share a biochemical reaction necessary for cell elongation so that the function of either one may bypass the loss of the function of the other. With the series of mutants, the chromosomal locus of the gene for each PBC was mapped: ponA (PBC-1a) 73.5 min, ponB (PBC-1b) 3.3 min, rodA (PBC-2) 14.4 min, ftsI (PBC-3) 1.8 min, dacB (PBC-4) 68 min, and dacA (PBC-5/6) 13.7 min.

Bacterial Proteins↗
PubMed1978

Isolation of a mutant of Escherichia coli lacking penicillin-sensitive D-alanine carboxypeptidase IA.

A mutant of Escherichia coli that is deficient in D-alanine carboxypeptidase IA has been isolated. The enzyme is membrane bound and moderately sensitive to penicillin. It catalyzes in vitro both D-alanine carboxypeptidase and transpeptidase reactions. Being able to synthesize crosslinked peptidoglycan both in vivo and in vitro despite the absence of enzyme activity, the newly isolated mutant grew normally under a wide range of growth conditions. Therefore, this enzyme, like D-alanine carboxypeptidase IB, is not required for normal peptidoglycan synthesis in E. coli. The defect in the activity of D-alanine carboxypeptidase IA in the mutant however was not associated with disappearance of penicillin-binding proteins 5 and 6 (which have been shown to be D-alanine carboxypeptidase IA) or any of the other protein bands that bind [14C]penicillin G. Genetic mapping studies showed that the mutation (dacA) is located close to leuS(13.7 min) on the E. coli chromosome map. Double mutants (dacA dacB) that are deficient in both D-alanine carboxypeptidases IA and IB were obtained. These double mutants also were found to grow normally and to catalyze normal formation of crosslinked peptidoglycan.

Carboxypeptidases↗
PubMed1978

Isolation of Q nucleoside precursor present in tRNA of an E. coli mutant and its characterization as 7-(cyano)-7-deazaguanosine.

One of the E. coli mutants selected for deficiency of modified nucleoside Q was found to contain an analogue of Q and normal guanosine in place of Q. The analogue of Q, designated as preQo, was isolated on a large scale from purified tRNATyr containing preQo. The structure of preQo was determined to be 7-(cyano)-7-deazaguanosine by comparison of its ultraviolet absorption spectra, thin-layer chromatographic mobility and mass spectrum with those of synthetic material.

Escherichia coli↗
PubMed1978

Crystallization of arginine-, formylmethionine-tyrosine-, and glycine-transfer RNAs from Escherichia coli.

Crystals as large as 0.5 X 0.3 X 0.2 mm of purified arginine-transfer RNA from Escherichia coli have been prepared by a vapour diffusion method. X-ray diffraction photographs showed that the crystals gave reflections up to 3.7 A spacing. They have a trigonal space group P31 2 1 (OR P32 2 1) and cell-dimensions a=97.2, b=97.2, c=94.8A. Crystals of a mercury derivative of this transfer RNA have also been obtained, and an X-ray diffusion photography of one of them is presented. Formylmethionine-transfer RNA from E. coli was crystallized in various forms, and the appearance of the polymorphs was found to depend upon the amount of spermine in the solution from which the crystallization took place. Crystals of tyrosine-transfer RNA and glycine-transfer RNA have also been obtained.

Arginine↗
PubMed1978

Serum vitamin B12 levels of patients with rheumatoid arthritis.

To elucidate the role of vitamin B12 in the formation of anemia in patients with rheumatoid arthritis serum B12 levels were investigated in patients with rheumatoid arthritis, patients with osteoarthritis and normal subject. Serum B12 level in patients with rheumatoid arthritis was significantly higher than that in patients with osteoarthritis and normal subjects. Serum B12 level increased in proportion to Steinbrocker's stages, and was related more closely to hemoglobin concentration than to erythrocyte count and had a high correlation with alpha1- and alpha2-globulin.

Adult↗