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Biomedical subjects

T Ohta

Publications and source records attributed to T Ohta.

At least 1,387 records · Page 77Linked to original sources
PubMed1978

The reaction of tryptophan with cystine during acid hydrolysis of proteins. Formation of tryptathionine as a transient intermediate in a model system.

Under the conditions commonly used to hydrolyze proteins with 6 M HCl, tryptophan reacted with cystine to give a transient intermediate, which was isolated and identified as 2-(2-amino-2-carboxyethylthio)tryptophan (tryptathionine) by NMR studies, etc. Studies on the formation and degradation of the above compound showed that beta-3-oxoindolylalanine and cysteine, which were previously reported to be the main degradation products of tryptophan and cystine, respectively, are formed by the hydrolysis of this intermediate during the course of the reaction.

Amino Acids↗
PubMed1978

Electron microscopic observation on sperm penetration and pronuclear formation in the fish egg.

Unfertilized eggs of the medaka, Oryzias latipes were inseminated after being mechanically freed from the chorion. In the first step of penetration, as soon as it reached the vitelline surface, the whole spermatozoon was quickly enclosed by ooplasmic protrusions (fertilization cone) of the vitelline surface. In the second step, the egg plasma membrane fused with various regions of the plasma membrane of the enclosed spermatozoon; finally the sperm flagellum was also incorporated into the ooplasm. Initial disappearance of the nuclear envelope of the sperm with vesiculation at the apical region of the head is followed by dispersal of the sperm chromatin. The nuclear envelope is then reformed by fusion of elongated or flattened vesicles along the margin of dispersing nuclear chromatin. The mature male pronucleus has a large nucleolus within a wrinkled envelope. It seems that the fertilization process in this fish involves some features of that occurring in the marine invertebrate and the mammalian eggs.

Animals↗
PubMed1978

Sequence variability of immunoglobulins considered from the standpoint of population genetics.

The probability of gene identity between members of a multigene family was investigated, assuming mutation, random genetic drift, and unequal crossing-over. The theoretical results on the equilibrium and transient behavior of the identity probability were applied to the analyses of sequence variability in the variable regions of immunoglobulins. The probability of amino acid identity between corresponding residue sites at different but homologous immunoglobulin sequences was computed both within and between species from data reported by other workers. The average probability of amino acid identity was obtained for the hypervariable regions and also for the framework regions. From statistical analyses based on population genetics theory it is concluded that somatic mutations cannot be the major cause of hypervariability and that the results can readily be explained by the germ line theory.

Journal Article↗
PubMed1978

Stepwise mutation model and distribution of allelic frequencies in a finite population.

A mathematical theory is developed that enables us to derive a formula for the equilibrium distribution of allelic frequencies in a finite population when selectively neutral alleles are produced in stepwise fashion (stepwise mutation model). It is shown that the stepwise mutation model has a remarkable property that distinguishes it from the conventional infinite allele model (Kimura-Crow model): as the population size increases indefinitely while the product of the effective population size and the mutation rate is kept at a fixed value, the mean number of different alleles contained in the population rapidly reaches a plateau which is not much larger than the effective number of alleles (reciprocal of homozygosity).

Alleles↗
PubMed1978

Detection of mutagenicity of the colon carcinogen 1,2-dimethylhydrazine by the host-mediated assay and its correlation to carcinogenicity.

Mutagenic potential of 1,2-dimethylhydrazine (DMH) was investigated in the host-mediated assay with mice used as hosts. This assay revealed potent mutagenicity of this colon carcinogen for Salmonella typhimurium G46. The mutagenicity of DMH was inhibited by pretreatment of mice with disulfiram. In addition, mouse strain and sex differences influenced the mutation induction by DMH: Mutation induction was significantly lower in C57BL/6 mice than in outbred ICR mice of either sex and was generally higher in male than in females of either C57BL/6 or ICR mice.

Animals↗