LOCALIZATION OF METMYOGLOBIN-REDUCING ENZYME (NADH-CYTOCHROME-B(5) REDUCTASE) SYSTEM COMPONENTS IN BOVINE SKELETAL-MUSCLE

Localization of metmyoglobin-reducing enzyme system components (NADH-cytochrome b5 reductase, cytochrome b5, outer mitochondrial membrane cytochrome b) was demonstrated in bovine skeletal muscle by immunohistochemical techniques. Both NADH-cytochrome b5 reductase and OM cytochrome b were located in red fibers. However, localization of cytochrome b5 did not show a definite difference between fiber types. Using an immunoblotting technique, NADH-cytochrome b5 reductase was found predominantly in the mitochondrial fraction, but it was also detected at lower levels in the microsomal fraction. OM cytochrome b was found predominantly in the mitochondrial fraction, but cytochrome b5 was detected only in the microsomal fraction. The results from this study, along with previous work about the localization of myoglobin in muscle, suggest that NADH-cytochrome b5 reductase reduces metmyoglobin by using OM cytochrome b at the mitochondrial surface and, in part, by using cytochrome b5 at the sarcoplasmic reticulum.