On Functional Role of Cytochrome b₅

I. NADH-linked Cytochrome c Reductase in Microsomes

Abstract

1) The participation of cytochrome b₅ in the mierosomal NADH-cytochrome c reductase activity was kinetically studied. Most of the activity could be ascribed to the action of cytochrome b₅.
2) Steady-state kinetics of the NADH-cytochrome c reductase activity of intact microsomes has revealed that the enzyme follows a so-called ping-pong mechanism. This is also true for the mechanism of NADH-linked reduction of solubilized cytochrome b₅, when catalyzed by intact microsomes.
3) The non-ionic detergent, Emalgen 810, has been used for the study of the mierosomal cytochrome b₅ system. The detergent inhibits the reduction of mierosomal bound cytochrome b₅, as well as the NADH-cytochrome c reductase activity of microsomes. In contrast, the detergent accelerates the NADH- “soluble” cytochrome b₅ reductase activity of microsomes.
4) Liver microsomes, when treated with the detergent, exhibit an enzymic activity for the reduction of metmyoglobin or methemoglobin by NADH.