Subcellular Distribution of Sulfite Cytochrome c Reductase in Rat Liver Tissue

The intracellular distribution of sulfite cytochrome c reductase was investigated in homogenates of rat liver and compared with the distribution of cytochrome oxidase, acid phosphatase, catalase and glucose‐6‐phosphatase which were used respectively as reference enzymes for mitochondria, lysosomes, peroxisomes and endoplasmic reticulum. 60% of the enzyme is recovered in the mitochondrial fraction, the remainder being found principally in the soluble fraction.The total mitochondrial fraction was analyzed by differential centrifugation in a stabilizing sucrose gradient and by isopycnic centrifugation in a sucrose gradient. The distribution curves of sulfite cytochrome c reductase are similar to those of two mitochondrial enzymes, cytochrome oxidase and adenylate kinase, and quite different from those of reference enzymes of other particles.Sulfite cytochrome c reductase exhibits a structure‐linked latency. The enzyme can be unmasked and solubilized by hypotonic treatment and by digitonin. In the activation experiments, its behaviour was similar to that of adenylate kinase and different from that of glutamate dehydrogenase.These findings are discussed in the light of the results of other authors. It is concluded that most of the rat liver sulfite cytochrome c reductase is associated with the mitochondria and is probably situated in the intermembrane space of these granules.