INVOLVEMENT OF CYANIDE-RESISTANT AND ROTENONE-INSENSITIVE PATHWAYS OFMITOCHONDRIAL ELECTRON-TRANSPORT DURING OXIDATION OF GLYCINE IN HIGHER-PLANTS

Metabolism of glycine in isolated mitochondria and protoplasts was inv estigated in photosynthetic, etiolated (barley and pea leaves) and fat -storing (maize scutellum) tissues using methods of [1-C-14]glycine in corporation and counting of (CO2)-C-14 evolved, oxymetric measurement of glycine oxidation and rapid fractionation of protoplasts incubated in photorespiratory conditions with consequent determination of ATP/AD P ratios in different cell compartments, The involvement of different paths of electron transport in mitochondria during operation of glycin e decarboxylase complex (GDC) was tested in different conditions, usin g aminoacetonitrile (AAN), the inhibitor of glycine oxidation in mitoc hondria, rotenone, the inhibitor of Complex I of mitochondrial electro n transport, and inhibitors of cytochrome oxidase and alternative oxid ase, It was shown that glycine has a preference to other substrates ox idized in mitochondria only in photosynthetic tissue where succinate a nd malate even stimulated its oxidation, Rotenone had no or small effe ct on glycine oxidation, whereas the role of cyanide-resistant path in creased in the presence of ATP, Glycine oxidation increased ATP/ADP ra tio in cytosol of barley protoplasts incubated in the presence of CO2, but not in the CO2-free medium indicating that in conditions of high photorespiratory nus oxidation of NADH formed in the GDC reaction pass es via the non-coupled paths, Activity of GDC in fat-storing tissue co rrelated with the activity of glyoxylate-cycle enzymes, glycine oxidat ion did not reveal preference to other substrates and the involvement of paths non-connected with proton translocation was not pronounced, I t is suggested that the preference of glycine to other substrates oxid ized in mitochondria is achieved in photosynthetic tissue by switching to rotenone-insensitive intramitochrondrial NADH oxidation and by inc reasing of alternative oxidase involvement in the presence of glycine. (C) 1997 Federation of European Biochemical Societies.