ACTIVATION OF GLYCINE DECARBOXYLASE IN PEA LEAF MITOCHONDRIA BY ATP

Activity of glycine decarboxylase decreased by 60-70% after the isolat ed pea leaf mitochondria were aged for 5 h in the absence of glycine a nd was completely lost after 24 h. The reverse reaction, i.e., product ion of glycine from serine, ammonium, dihydrolipoate, and bicarbonate, was also inhibited in these aged mitochondria. Glycine decarboxylase could be reactivated by both exogenous and endogenous ATP. The latter was formed during the oxidation of succinate, malate, or oxoglutarate. Glycine decarboxylase consists of four subunits (P-, H-, L-, and T-pr oteins). The aged mitochondria were able to catalyze the exchange of [ C-14]bicarbonate-glycine and the oxidation of dihydrolipoate, indicati ng the persistence of P-, H-, and L-protein activities. Serine hydroar ymethyltransferase catalyzes the formation of serine from methylene te trahydrofolate and another glycine molecule at the last reaction of gl ycine oxidation. The aged mitochondria were able to catalyze the forma tion of methylene tetrahydrofolate from [C-14]serine and its reverse r eaction. Therefore, it was concluded that the loss of glycine decarbox ylase activity was due to an inhibition of the reaction catalyzed by T -protein, which required ATP for its activation. (C) 1995 Academic Pre ss, Inc.