Diaminobenzidine reactions in control and treated Amoeba proteus.

Cytochrome oxidase activity was demonstrated in Amoeba proteus by diaminobenzidine (DAB) cytochemistry. Deposition of the reaction product occurred on the inner mitochondrial membranes and the cristae. The reaction was abolished by cyanide incubations. Positive reactions were produced with both unfixed and fixed cells: although staining potential was destroyed by any prefixatives which included glutaraldehyde. Cells prefixed with 4% formaldehyde, to raise structural preservation, retained staining ability. Amoebae subjected to prolonged anaerobiosis or to treatment with the carcinogen N-methyl-N-nitrosourethane (MNU) displayed a reduction in DAB reactivity. A positive reaction was only produced in incubations of unfixed cells and even in these the intensity of cristal staining was depleted. The possible use of DAB reactions where lesions in mitochondrial functioning have occurred is considered.