Gastric microsomal NADH-cytochrome b5 reductase: characterization and solubilization.

1.1. NADH-cytochrome b5 reductase from hog gastric microsomes was studied with respect to substrate dependence, optimum pH, thermal denaturation as well as anti-cytochrome b5 antibodies and different ions.2.2. The reduction of potassium ferricyanide by the enzyme was specific for NADH.3.3. Using potassium ferricyanide or trypsin-solubilized liver cytochrome b5 (Tb5) as substrates, enzyme activity was inhibited by ADP and to a lesser extent by ATP.4.4. Tb5- (but not ferricyanide-) reductase was activated by ionic strength up to 0.05 ion equivalent per liter and inhibited at higher strengths whatever the ion used (Cl−, Na+, Ca2+, Mg2+).5.5. Enzyme solubilization occurred with Triton X100. The solubilization increased the Tb5- (but not the ferricyanide-) reductase activity up to a Triton:protein ratio of 15.6.6. We therefore suggest that gastric microsomes contain a Triton soluble membrane-bound NADH cytochrome b5 reductase which is in many respects similar to the liver and red cell enzymes.