Nitrate reductase of Chlorella fusca: Partial purification, cytochrome content and presence of HCN after in vivo inactivation.

An inactivated nitrate reductase (EC 1.6.6.1) formed in vivo by the green alga Chlorella fusca Shihira and Kraus is shown to be a cyanide complex. The partially purified inactive enzyme releases 0.048 nmol of HCN per unit of enzyme activated. This compares with 0.066 nmol of HCN liberated in similar previous measurements with the inactivated enzyme from Chlorella vulgaris. The nitrate reductase from C. fusca has been purified to a level of 67 μmol nitrate reduced per min per mg enzyme. It contains a cytochrome b557, at a level 1.9-fold higher per unit of active enzyme, than the nitrate reductase from C. vulgaris.