Search PubMed⌕ Search

Biomedical subjects

Y Hirota

Publications and source records attributed to Y Hirota.

At least 541 records · Page 30Linked to original sources
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

Function of phospholipids in Escherichia coli. Characterization of a mutant deficient in cardiolipin synthesis.

Screening of a collection of temperature-sensitive mutants of Escherichia coli for defects in phospholipid metabolism led to the isolation of a mutant deficient in cardiolipin synthesis. The defective gene, named cls, is closely linked to the trp marker and maps at about Minute 27 on the E. coli chromosome. After transfer of cls to a defined genetic background by transduction, the mutant has the following properties as compared to an isogenic wild type. Exponentially growing cells show a reduction in cardiolipin content by a factor of at least 15 (less than 0.2 mol % of the total phospholipids). A crude membrane fraction derived from the mutant is unable to synthesize cardiolipin from phosphatidylglycerol in vitro. The mutant has no distinctive phenotype regarding its growth properties, membrane-associated respiratory functions, or the ability to insert bacteriophage M13 coat protein into the cell envelope. The cls mutation confers a 5-times reduction in the turnover of the phosphate moiety of phosphatidylglycerol.

Cardiolipins↗
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↗