Physiological correlation between nucleoside-diphosphate kinase and the enzyme-associated guanine nucleotide binding proteins

Abstract

The physiological correlation between NDP-kinase and the enzyme-associated guanine nucleotide binding proteins (G1 and G2) has been studied in vitro . It was found that (i) incubation of the phosphoenzyme (enzyme-bound high-energy phosphate intermediate) of NDP-kinases with one of the nucleoside 5′-diphosphates (NDPs) in the presence of divalent cations (Mg 2+ and Ca 2+) results in the formation of nucleoside 5′-triphosphates (NTPs) within 40 sec even at low temperatures (below 4°C) without strict base-specificity; and (ii) high-energy phosphates on the phosphoenzyme can transfer preferentially to GDP on the guanine nucleotide binding proteins (G1, G2 and r-p21 protein) in the presence of 0.25 mM Ca 2+ or 1 mM Mg 2+ even if any other NDPs are present in the reaction mixtures. These observations suggest that NDP-kinase may be responsible for the phosphate-transfer between GDP on the guanine nucleotide binding proteins and its phosphoenzyme.