Effect of stabilizers on diaminobenzidine reactions of mitochondria

The effect of various stabilizers--0.9% NaCl, 7.5% sucrose and 7.5% polyvinyl pyrrolidone (PVP) on reactions of mitochondria with fresh and photooxidized diaminobenzidine (DAB) was investigated. NaCl and PVP abolished the DAB staining of mitochondria incubated without exogenous cytochrome c; NaCl, however, was ineffective when exogenous cytochrome c or oxidized DAB were present in the incubation medium. PVP considerably decreased the intensity of all reactions performed in the presence of exogenous cytochrome c or oxidized DAB. The mechanism of the observed effect is not likely to involve osmotic protection of mitochondria; extraction of endogenous cytochrome c from fresh frozen tissue by NaCl and greatly increased viscosity of PVP-containing media seem to be most probable explanations.