Iso-enzymes of acid ribonuclease in cotyledons of Pisum sativum L.

Acid ribonuclease from cotyledons of Pisum sativum is very stable, with a temperature optimum of 65° C. It has a molecular weight of 17,500 and there is evidence that a fragment, with a molecular weight of 3,100, retains enzyme activity. Acid ribonuclease from the cotyledons of five-day old seedlings may be fractionated into two iso-enzymes, I and II, by CM-cellulose chromatography. The increase in activity of iso-enzyme I is not inhibited by cycloheximide, whereas the increase in iso-enzyme II activity is strongly inhibited by cycloheximide. Cotyledons of 9-day old seedlings contain only iso-enzyme I, whilst cotyledons of 15-day old seedlings contain three iso-enzymes, I, IIa and III.