Cyanide - Enzyme-activity Control

Plants generate cyanide from cyanogenic glucides and histidines. Ethylene biosynthesis is also accompanied by cyanide production. Nitrate reductase can occur in reduced form following its interaction with NADH in the absence of nitrate. The reduced form of the enzyme has the ability to combine with cyanide forming enzyme-CN complex which is enzymatically inactive. Nitrate, blue light or oxygen oxidise the enzyme-CN complex releasing cyanide.

The cyanide free enzyme regains its activity. Hydroxyl amine or superoxide inactivates the enzyme which on exposure to blue light gets converted to active form. It is observed that plants grown in blue light are higher in protein contents. Blue light regulation of nitrate reductase activity may be one of the primary factors responsible for higher protein synthesis.