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Biomedical subjects

M Nishikimi

Publications and source records attributed to M Nishikimi.

At least 109 records · Page 6Linked to original sources
PubMed1980

Oxidation by superoxide of tocopherols dispersed in aqueous media with deoxycholate.

alpha-Tocopherol dispersed in aqueous media with deoxycholate was found to be oxidized, at a physiological pH, by a xanthine-xanthine oxidase system. This reaction was completely inhibited by the addition of superoxide dismutase, whereas catalase and mannitol (scavenger of hydroxyl radical) did not affect the reaction. This finding indicates that the oxidation of alpha-tocopherol is caused by O2. The reaction product formed was identified as 8 alpha-hydroxy-alpha-tocopherone by thin-layer chromatography and ultraviolet spectroscopy. The product was found to change spontaneously to alpha-tocopherol quinone. beta-, gamma-, and delta-tocopherol dispersed with deoxycholate also reacted with O2. The reaction of tocopherols dispersed in the micellar form may be considered as a model of in vivo reaction of tocopherols, since tocopherols are present in tissues largely in the membranes, where O2 is known to be generated.

Ascorbic Acid↗
PubMed1980

A possible function of thiols, including glutathione, as cofactors in the conversion of thyroxine to 3,3',5-triiodothyronine in rat liver microsomes.

Thyroxine (T4) is known to be converted to triiodothyronine (T3) in rat liver microsomes. An endogenous stimulatory factor for the conversion of T4 to T3 was identified as reduced glutathione (GSH) by Sephadex G-15 gel chromatography of rat liver extract. The production of T3 in rat liver microsomes was maximally stimulated above a GSH concentration of 4mM, and an approximately 5-fold stimulation was attained. This degree of stimulation was approximately 10 time less than that observed with dithiothreitol (DTT). Activity in the conversion of T4 to T3 was solubilized from the microsomes using 0.1% deoxycholate. When the solubilized microsomal preparation, pre-treated with DTT or GSH, was subjected to gel filtration on a Sepharose CL-6B column to separate the preparation from the thiol, almost no T3 producing activity was observed in any of the collected fractions. However, when DTT or GSH was added to the fractions containing high molecular weight components, the activity of the production of T3 was sustained. This finding indicates that these thiols play an essential role in the conversion of T4 to T3, possibly acting as cofactors.

Animals↗
PubMed1976

Immunologic evidence that the gene for L-gulono-gamma-lactone oxidase is not expressed in animals subject to scurvy.

L-Gulono-gamma-lactone oxidase (L-gulono-gamma-lactone:oxygen 2-oxidoreductase, EC 1.1.3.8) is the enzyme that catalyzes the terminal step of L-ascorbic acid biosynthesis in mammalian liver. The absence of the oxidase activity in primates and guinea pigs is the reason why these animals are subject to scurvy, which must be considered an inborn error of metabolism. Attempts were made to determine if a protein immunologically crossreactive with L-gulono-gamma-lactone oxidase is present in these animals. Detergent-solubilized microsomal preparations from guinea pig and African green monkey liver did not precipitate the antisera directed to either rat or goat enzyme, nor did any of the other cell fractions obtained from guinea pig liver react with either antiserum. No crossreactive protein was detectable in guinea pig microsomes even with the sensitive procedure or micro-complement fixation. On the other hand, extracts of all 10 other mammalian (4 orders) liver microsomes tested were shown to contain L-gulono-gamma-lactone oxidase activity that did crossreact with antibodies to the rat and goat enzymes. One explanation of these findings is that, in the guinea pig, and perhaps in primates too, the structural gene for L-gulono-gamma-lactone oxidase is not expressed.

Alcohol Oxidoreductases↗