FMO5 and myocardial infarction: The expression of gp91phox (a key component of NADPH oxidase which is the most important superoxide-producing enzyme in the ischemic reperfused heart) was also markedly upregulated while catalase and MnSOD levels were downregulated in the MI/R-treated group (Figures 4(c)-4(f), compared with the sham group).