INACTIVATION OF LIPOAMIDE DEHYDROGENASE BY COBALT(II) AND IRON(II) FENTON SYSTEMS - EFFECT OF METAL CHELATORS, THIOL COMPOUNDS AND ADENINE-NUCLEOTIDES

Fe(II)-and Co(II)-Fenton systems (FS) inactivated the lipoamide reduct ase activity but not the diaphorase activity of pig-heart lipoamide de hydrogenase (LADH). The Co(II) system was the more effective as LADH i nhibitor. Phosphate ions enhanced the Fe(II)-FS activity. EDTA, DETAPA C, DL-histidine, DL-cysteine, glutathione, DL-dithiothreitol, DL-lipoa mide, DL-thioctic acid, bathophenthroline, trypanothione and ATP, but not ADP or AMP, prevented LADH inactivation. Reduced disulfide compoun ds were more effective protectors than the parent compounds. Mg ions c ounteracted ATP protective action. Glutathione and DL-dithiothreitol p artially restored the lipoamide dehydrogenase activity of the Fe(II)-F S-inhibited LADH. DL-histidine exerted a similar action on the Co(Il)- FS-inhibited enzyme. Ethanol, mannitol and benzoate did not prevent LA DH inactivation by the assayed Fenton systems and, accordingly, it is postulated that site-specific generated HO' radicals were responsible for LADH inactivation. With the Co(II)-FS, oxygen reactive species oth er than HO', might contribute to LADH inactivation.