Interactions between NADH-Cytochrome b₅ Reductase and Cytochrome b₅ Preparations Purified from Liver Microsomes

抄録

Two types of NADH-cytochrome b₅ reductase [EC 1. 6. 2. 2] (fp₁) preparations, one solubilized by treatment with detergents (d-fp₁) and the other solubilized by digestion with lysosomes (l-fp₁), and two types of cytochrome b₅ preparations, one solubilized with detergents (d-b₅) and the other by tryptic digestion (t-b₅), were used to study the interactions between the flavoprotein and the cytochrome. The functional interactions were studied by measuring the NADH-cytochrome c reductase activity reconstituted from the flavoprotein and the cytochrome. Among the four possible combinations tested, the system consisting of d-fp₁ and d-b₅ was by far the most efficient with respect to the maximal cytochrome c-reducing activity and the cytochrome b₅ concentration giving half maximal activity. Gel filtration on a Sepharose 6B column indicated that a functional aggregate of large particle size was formed on mixing d-fp₁ and d-5₅. However, no aggregate was detected when d-fp₁ was mixed with t-b₅ or trypsin-treated d-b₅. It is concluded that aggregate formation was principally responsible for the high catalytic activity of the system consisting of d-fp₁ and d-b₅.