Purified cryptocytochrome-c of Pseudomonas denitrificans was separated by starch gel electrophoresis at pH 6.0(M/80 citrate buffer) to a cathodical non-heme denitrifying enzyme, a less migrating reddish cryptocytochrome c and an anodic non-enzyme protein. Cryptocytochrome-c could not replace cyto-chrome c1552 in the denitrifying enzyme-nitrite (or hydroxylamine) system.