Search PubMed⌕ Search

Biomedical subjects

S Otsuka

Publications and source records attributed to S Otsuka.

At least 109 records · Page 6Linked to original sources
PubMed1982

[Changes of natural killer activity following local 60Co irradiation in intracranial tumor-bearing mice (author's transl)].

Changes of natural killer activity (NK activity) by local 60Co irradiation in intracranial tumor-bearing mice were studied by the method of 51Cr release assay. Local irradiation was administered 10 days after intracranial transplantation of 203-Glioma which had been originally induced by 20-methylcholanthrene in C 57 BL mice. Irradiation suppressed the growth of tumor and prolonged the mean survival time. The 50% survival time of untreated mice was about 2.5 weeks but that of mice treated by a single dose of 1000 rad and 1500 rad of irradiation was about 4.5 weeks and 6.5 weeks respectively. NK activity of spleen cells in these mice was serially examined. NK activity was gradually increased in mice treated by local irradiation, while it was gradually decreased in mice without treatment. On the other hand, NK activity remained unchanged in non-tumor-bearing control mice. Mice treated with 1000 rad and 1500 rad of irradiation showed 44.0% and 47.6% of % specific 51Cr release respectively 11 days after irradiation while normal mice showed 18.0%. The increased NK activity after local irradiation suggested that local irradiation might have enhanced the immunological defence mechanism against the tumor in the tumor-bearing hosts. Some characteristics of effector cells in this assay system were examined. The cytotoxicity of spleen cells was removed by the treatment of anti-BAT serum and complement but was not removed by the treatment of anti-Thy-1. 2 serum and complement. Since NK activity reflects the immunological resistance to tumors to some extent, it is felt important to clarify the significance of changes of NK activity in patients with brain tumors in relation to various treatments including surgery, radiotherapy, chemotherapy and immunotherapy in the next step.

Animals↗
PubMed1981

The reaction of oxygen with protocatechuate 3,4-dioxygenase from Pseudomonas putida. Characterization of a new oxygenated intermediate.

The reactions of protocatechuate dioxygenase (protocatechuate:oxygen 3,4-oxidoreductase, EC 1.13.11.3) with substrates and oxygen have been studied at 4 degrees C using rapid kinetic techniques. In this study, two oxygenated intermediates were kinetically and spectrally characterized. The rate of oxygen addition to the enzyme-substrate complex was determined to be 5 X 10(5) M-1 s-1. This oxygenated complex rapidly converts (450 s-1) to another spectrally identifiable compound which then breaks down into free enzyme and the product, beta-carboxy-cis,cis-muconic acid. To carry out these experiments properly, it was necessary to use hyperbaric oxygen, thus obtaining approximately 6 mM final concentration of oxygen. The procedure is described in this work. It was also shown that the normally slow substrate, dihydroxyphenyl propionate, when reacted with the enzyme and oxygen, rapidly forms two sequential intermediates. However, the second intermediate was not spectrally the same as that observed with protocatechuate, but was more like that of enzyme-product complexes. Similar, although less extensive, studies using the protocatechuate dioxygenase from Pseudomonas aeruginosa showed that very analogous behavior occurred with both substrates as did with the Pseudomonas putida enzyme.

Binding Sites↗
PubMed1981

Structure, assembly, conformation, and immunological properties of the two subunit classes of ferritin.

The two subunit types of human liver ferritin were purified to homogeneity. Both subunits reassembled in a well-defined manner and formed spherical particles that resembled natural apoferritin in electron micrographs. Affinity chromatography methods were employed to obtain preparations of antibodies that interacted exclusively either with the H or with the L polypeptides, demonstrating that distinct immunological properties may be ascribed to each subunit of ferritin. The amino acid compositions of the subunits were similar, but the larger H subunit had fewer leucine, phenylalanine, and arginine residues. It is therefore improbable that H subunits undergo proteolytic processing and are precursors for L subunits. Circular dichroism data indicated that homopolymers assembled from L-type subunits had substantially more ordered secondary structures and greater alpha-helical contents than their H counterparts. Small differences in the environment of tryptophan residues were evident from fluorescence spectra of each homopolymer. In isoelectric focusing experiments reassembled H or L homopolymers migrated as families of proteins within discrete pI ranges which are probably representative of subpopulations of each subunit type. The H homopolymer focused at lower pI's than the L component. These data substantiate the contention that both subunits are authentic polypeptide moieties of ferritin with some common structural features, but the results also underscore prominent dissimilarities in their properties.

Apoferritins↗
PubMed1980

Assembly of intra- and interspecies hybrid apoferritins.

An intraspecies hybrid apoferritin was assembled by mixing subunits of horse heart ferritin, which consists mainly of H-type subunits, and horse spleen ferritin, in which L-type subunits predominate. Interspecies hybrid apoferritins were reconstituted from subunits of human liver-horse spleen ferritins and from rat liver-horse spleen ferritins. All the hybrid ferritins migrated as single zones with electrophoretic mobilities intermediate between those of the parent ferritins. Isoelectric focusing data and immunological patterns were consistent with the view that the reassembled apoferritins were composite molecules that contained subunits from each of the interacting forms. Reconstitution occurred in a random manner, as there was no apparent preference for assembly of homologous subunits. These results suggest that intersubunit interaction domains and recognition mechanisms that dictate formation of the highly specific quaternary structure assumed by this protein are common for different species of ferritins.

Animals↗