ONE-ELECTRON AND 2-ELECTRON REDUCTION OF MENADIONE IN GUINEA-PIG AND RAT CARDIAC TISSUE

1. In both guinea-pig and rat heart, mitochondrial NADH-ubiquinone-reductase and soluble DT-diaphorase accounted for 49-50% and 48-50% of menadione metabolism, respectively. Microsomal NADPH-cytochrome P450-reductase was responsible for < 1% of menadione reduction. 2. Menadione was a high-affinity substrate for all reductases (K(m) values from 1 to 10-mu-M). 3. Marked amounts of O2.- (superoxide anion) were generated as a consequence of cardiac metabolism of menadione. 4. Menadione-induced O2.- generation was about 3-fold higher in guinea-pig than in rat heart. 5. All results were compared with data obtained on guinea-pig and rat liver.