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Biomedical subjects

G Kikuchi

Publications and source records attributed to G Kikuchi.

At least 37 records · Page 2Linked to original sources
PubMed1982

Identification of the product of heme degradation catalyzed by the heme oxygenase system as biliverdin IX alpha by reversed-phase high-performance liquid chromatography.

Biliverdins formed from heme by a microsomal preparation and a reconstituted heme oxygenase system were each converted to their dimethyl esters and analyzed for isomeric composition by reversed-phase high-performance liquid chromatography, using a column of mu Bondapak C18 (Waters Associates); on this column, the dimethyl esters of four biliverdin IX isomers, that is IX alpha, IX beta, IX gamma, and IX delta, have been shown to be eluted separately in the order IX alpha, IX beta, IX delta, and IX gamma, when developed with methanol/water. The analysis indicated that the enzymatically formed biliverdins were exclusively IX alpha; the elution profile exhibited no other significant elution peak due to other biliverdin isomers. It was concluded that the heme oxygenase system cleaves the heme ring specifically at the alpha-methene bridge to yield biliverdin IX alpha.

Animals↗
PubMed1982

The mitochondrial glycine cleavage system: differential inhibition by divalent cations of glycine synthesis and glycine decarboxylation in the glycine-CO2 exchange.

The exchange of glycine carboxyl carbon with CO2 catalyzed by the combination of chicken liver glycine decarboxylase (P-protein) and aminomethyl carrier protein (H-protein) was markedly inhibited by various divalent cations, although extents of inhibition by individual metal ions varied considerably. Cu2+ and Zn2+, at 100 microM, inhibited the reaction almost completely, and the inhibitions by Co2+ and Ni2+ were also significant, while Mg2+ and Mn2+ did not appreciably affect the reaction. The inhibition by Zn2+ was competitive with both bicarbonate and H-protein and non-competitive with glycine. Of the two reactions involved in the glycine-CO2 exchange, decarboxylation of glycine yielding the H-protein-bound aminomethyl moiety was not significantly affected by 100 microM Zn2+ or Cu2+, but carboxylation of the H-protein-bound aminomethyl moiety to form glycine was strongly inhibited by either Zn2+ or Cu2+. Various degrees of inhibition of the glycine-CO2 exchange by other divalent metal ions could also be accounted for by the inhibition of the carboxylation step of the exchange reaction. The primary site of the action of divalent metal ions is likely to be not P-protein but H-protein, and the binding of metal ions with the H-protein-bound intermediate of glycine decarboxylation was assumed to account for the observed marked inhibition.

Animals↗
PubMed1982

The mitochondrial glycine cleavage system: inactivation of glycine decarboxylase as a side reaction of the glycine decarboxylation in the presence of aminomethyl carrier protein.

Glycine decarboxylase, tentatively called P-protein, was inactivated when it was incubated with glycine in the presence of the aminomethyl carrier protein, called H-protein. The inactivation was accompanied by a spectral change in the P-protein as a pyridoxal phosphate enzyme; the spectrum became unusual, with a peak at 330 nm. The fluorescence emission spectrum of the inactivated P-protein showed a distinct peak at 390 nm when excited at 325 nm. Such a spectral change and concomitant inactivation of the P-protein could be completely prevented by the addition of sodium bicarbonate, which initiates the glycine-CO2 exchange in the reaction mixture. The inactivated P-protein was associated with H-protein and the methylene carbon of glycine, but not the carboxyl carbon, in a manner not separable by gel filtration, although the molar ratios of those three components were not constant. The H-protein recovered in the inactivated P-protein fraction was also catalytically inactive. Neither the pyridoxal derivative nor the methylene carbon of glycine appeared to be covalently bound with the protein, and the methylene carbon could be recovered as formaldemethone when treated with dimedone. The inactivation of the P-protein appears to represent a suicide reaction of the P-protein as a side reaction of the glycine decarboxylation, which is supposed to involve the formation of a ternary complex of P-protein, aminomethyl moiety of glycine and H-protein through a Schiff base linkage of the H-protein-bound amino-methyl moiety with the pyridoxal phosphate of P-protein.

Amino Acid Oxidoreductases↗
PubMed1981

Degradation of mesoheme and hydroxymesoheme catalyzed by the heme oxygenase system: involvement of hydroxyheme in the sequence of heme catabolism.

Mesoheme bound to heme oxygenase protein was easily degraded to mesobiliverdin by incubation with NADPH-cytochrome c reductase and NADPH. The features of mesoheme degradation were very similar to those of protoheme degradation catalyzed by the heme oxygenase system; an intermediate compound having its absorption maximum at 660 nm appeared in the couse of mesoheme degradation and this compound is presumably equivalent to the 688 nm compound which appears in the course of protoheme degradation. Hydroxymesoheme was chemically prepared and a complex of hydroxymesoheme and heme oxygenase was prepared. The complex was fairly stable in air, but when the complex was incubated with the NADPH-cytochrome c reductase system, the hydroxymesoheme bound to heme oxygenase was readily converted to mesobiliverdin through the 660 nm compound as an intermediate. It is evident that hydroxyheme is a real intermediate of heme degradation in the heme oxygenase reaction and that the 688 nm compound (or the 660 nm compound in the mesoheme system) is located between hydroxyheme and the biliverdin-iron chelate. The ferrous state of heme-iron may also be necessary for the onset of further oxidation of hydroxyheme.

Animals↗