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

Hiraga, K.; Kikuchi, G.

Journal of Biochemistry 92(5): 1489-1498


ISSN/ISBN: 0021-924X
PMID: 7153213
Accession: 006719095

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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 3 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 aminomethyl moiety with the pyridoxal phosphate of P-protein.