PRODUCTION OF SUPEROXIDE RADICALS IN GLYOXYSOMAL MEMBRANES FROM CASTOR BEAN ENDOSPERM

The production of superoxide free radicals (O-2-radical-anion) by NADH was investigated in glyoxysomal membranes from germinating castor bean (Ricinus communis L., cv. Hale) endosperm purified by treatment with 0.1 M Na2CO3. About 25 % of the NADH:cytochrome c reductase activity in glyoxysomal membranes was mediated by O-2-radical-anion radicals induced by NADH. The rate of superoxide production by glyoxysomal membranes from castor bean endosperm (about 27 nmol O-2-radical-anion x mg(-1) protein x min(-1)) was the highest measured so far in peroxisomal membranes. Incubation of membranes with an antibody against whole glyoxysomal membrane proteins from castor bean endosperm produced an inhibition of about 40 % in the NADH-dependent O-2-radical-anion generation, whereas the O-2-radical-anion-independent NADH:cytochrome c reductase activity was not affected. A superoxide dismutase isoenzyme was detected by native gel electrophoresis and characterized as a Mn-superoxide dismutase, and appeared to be a peripheral protein of glyoxysomal membranes. The NADH-induced generation of O-2-radical-anion radicals by glyoxysomal membranes from castor bean endosperm supports the idea that the production of superoxide is a common metabolic property of peroxisomal membranes. The possible function of Mn-superoxide dismutase in glyoxysomal membranes is discussed.