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Biomedical subjects

M Ohki

Publications and source records attributed to M Ohki.

At least 181 records · Page 10Linked to original sources
PubMed1983

Enhancement of dengue virus type 2 replication in mouse macrophage cultures by bacterial cell walls, peptidoglycans, and a polymer of peptidoglycan subunits.

The effects of bacterial cell walls, peptidoglycans, and a water-soluble polymer of peptidoglycan subunits on dengue virus type 2 replication in cultured mouse peritoneal macrophages were studied. Pretreatment of macrophage cultures with all of test cell walls isolated from seven bacterial species for 3 days significantly enhanced the virus production in the cultures. Peptidoglycans prepared from four of the above cell walls also exerted the virus production-enhancing effects in a similar manner as the walls. A water-soluble polymer of peptidoglycan subunits which was prepared by treatment of Staphylococcus epidermidis wall peptidoglycan with an interpeptide bridge-splitting enzyme (endopeptidase) also definitely enhanced the virus production in macrophage cultures, although its activity was weaker than that of the original wall and peptidoglycan. Macrophage cultures from athymic nude mice, when treated with cell walls and peptidoglycans of S. epidermidis and Lactobacillus plantarum for 3 days, also showed an increased ability to support dengue virus type 2 replication. The infectious center assay demonstrated that the virus replication enhancement by S. epidermidis cell wall and peptidoglycan was primarily due to an increase in the number of virus-infected cells. This finding did not seem to be in conflict with the observation that macrophages treated with the above cell wall or peptidoglycan phagocytized more latex particles than did untreated macrophages. The conclusions based on the above experiments are that the treatment of mouse peritoneal macrophage cultures with bacterial cell walls and their components increases the take of dengue virus type 2 by macrophages and thus raises the virus production in the macrophage cultures.

Animals↗
PubMed1982

Pyridazinones. 1. Synthesis and antisecretory and antiulcer activities of thio amide derivatives.

In an effort to develop new types of antiulcer agents, a series of novel 3(2H)-pyridazinone derivatives and related analogues was synthesized. Substituted 3(2H)-pyridazinones and their 4,5-dihydro analogues were alkylated by omega-haloalkyl cyanides at the N-2 position under phase-transfer catalytic reaction, and the nitrile group was converted to the thio amide group by treatment with hydrogen sulfide alone or with the appropriate primary or secondary amines. Various substituents were introduced on the nitrogen of thio amide, on the carbon in the side chains, and on the 3(2H)-pyridazinone ring. The synthesized compounds were evaluated for gastric antisecretory activity in the pylorus-ligated rat, and selected compounds were applied to experimental ulcer models, such as Shay's, aspirin-induced, and stress-induced ulcers in the rat. Structure-activity relationships are discussed. 3(2H)-Pyridazinones with a C-6 phenyl group and an N-2 alkyl side chain with a terminal thio amide group (48, 49, 51, and 52) were the most potent among the compounds tested.

Animals↗
PubMed1982

Synthesis of mRNA of malB operons at specific stages in the cell cycle of Escherichia coli.

The mRNA synthesis of the malB operons was examined using synchronous cultures of Escherichia coli. mRNA of the malB operons were synthetized in cell cycle-specific manners different from the bulk mRNA synthesis. The synthesis occurred in two stages during a cell cycle, one in the middle of the cycle and the other at the time slightly before cell division. Identification of the species of mRNA revealed that the malK-lamB operon was preferably transcribed in the former stage of the cycle while a major fraction of mRNA of the malE-malF operon was synthesized in the later stage.

Cell Cycle↗
PubMed1979

A pleiotropic defect of membrane synthesis in a thermosensitive mutant tsC42 of Escherichia coli.

Synthesis of membrane proteins in a thermosensitive mutant of Escherichia coli K12, tsC42, that has a defect in a mechanism of cell cycle-dependent duplication of membrane enzymes was examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The cells were labeled differentially with [14C]- and [3H]arginine and the membrane proteins synthesized at nonpermissive and permissive temperatures were compared. The results showed that at the nonpermissive temperature, the syntheses of cytoplasmic membrane proteins and outer membrane proteins were reduced more than 70% and 50%, respectively. No significant accumulation of precursor molecules of membrane proteins at the nonpermissive temperature was detected in pulse-chase experiments. It is therefore assumed that the mutant has a defect in a gene that regulates the biosynthesis of many membrane proteins.

Arginine↗
PubMed1979

Genetic and biochemical studies of transport systems for branched-chain amino acids in Escherichia coli.

Mutants of Escherichia coli K-12 requiring high concentrations of branched-chain amino acids for growth were isolated. One of the mutants was shown to be defective in transport activity for branched-chain amino acids. The locus of the mutation (hrbA) was mapped at 8.9 min on the E. coli genetic map by conjugational and transductional crosses. The gene order of this region is proC-hrbA-tsx. The hrbA system was responsible for the uptake activity of cytoplasmic membrane vesicles. It was not repressed by leucine. The substrate specificities and kinetics of the uptake activities were studied using cytoplasmic membrane vesicles and intact cells of the mutants grown in the presence or absence of leucine. Results showed that there are three transport systems for branched-chain amino acids, LIV-1, -2, and -3. The LIV-2 and -3 transport systems are low-affinity systems, the activities of which are detectable in cytoplasmic membrane vesicles. The systems are inhibited by norleucine but not by threonine. The LIV-2 system is also repressed by leucine. The LIV-1 transport system is a high-affinity system that is sensitive to osmotic shock. When the leucine-isoleucine-valine-threonine-binding protein is derepressed, the high-affinity system can be inhibited by threonine.

Amino Acids, Branched-Chain↗
PubMed1979

Genetic studies of an Escherichia coli K-12 temperature-sensitive mutant defective in membrane protein synthesis.

The mutant divE42(Ts) of Escherichia coli K-12, defective in the synthesis of membrane proteins and in the transcription of the lac operon at high temperature, has been further characterized. It was found that a mutation (divE42) located at about min 22 on the E. coli chromosome map is responsible for the Lac- phenotype and temperature-sensitive growth. The mutation could be contransduced with serC, pyrD, or pyrC by phage P1 at a frequency of 4, 16, or 0.5%, respectively, the gene order being serC-pyrD-ompA-sulA-divE-pyrC. Examination of temperature-independent revertants and Pyr+ transductants revealed that all the mutant phenotypes examined (deficiencies in the increase of activities of some membrane enzymes, expression of the lac operon, and synthesis of several other proteins) are due to a single mutation (divE42) which is recessive to the wild-type (divE+) allele. Protein synthesis in the mutant was also analyzed by dodecyl sulfate-polyacrylamide gel electrophoresis. Synthesis of a number of proteins, including membrane proteins, was found to decrease significantly, whereas that of an elongation factor, EF-Tu, increased upon transfer of a log-phase culture to high temperature (42 degrees C). These effects of temperature shift-up on protein synthesis were evident within 5 min under the conditions used.

Bacterial Proteins↗