Subcellular localization and characterization of nucleoside diphosphate kinase in rat retina: Effect of diabetes

Nucleoside diphosphate kinase (NDP kinase) catalyzes the transfer of termin al phosphate from nucleotide triphosphates (e.g. ATP) to nucleotide diphosp hates (e.g. GDP) to yield nucleotide triphosphates (e.g. GTP). Since guanin e nucleotides play critical role(s) in GTP-binding protein (G-protein)-medi ated signal transduction mechanisms in retina, we quantitated NDP kinase ac tivity in subcellular fraction-derived from normal rat retina. A greater th an 85% of the total specific activity was present in the soluble fraction, which was stimulated (up to 7 fold) by 2 mM magnesium. NDP kinase exhibited saturation kinetics towards di- and tri-phosphate substrates, and was inhi bited by known inhibitors of NDP kinase, uridine diphosphate (UDP) or cromo glycate (CRG). We have previously reported significant abnormalities in the activation of G-proteins in streptozotocin (STZ)-diabetic rat retina (Kowl uru er al. Diabetologia 35:624-631, 1992). Since NDP kinase has been implic ated in direct interaction with and/or activation of various G-proteins, we quantitated both basal and magnesium-stimulated NDP kinase activity in sol uble and particulate fractions of retina derived from STZ-diabetic rats to examine whether abnormalities in G-protein function in diabetes are attribu table to alterations in retinal NDP kinase. There was no effect of diabetes either on the basal or the magnesium-activated retinal NDP kinase activity . This study represents the first characterization of NDP kinase activity i n rat retina, and suggests that in diabetes, this enzyme may not be rate-li miting and/or causal for the observed alterations in retinal G-protein func tions.