Proteinases and Enzyme Stability in Crude Extracts of Castor Bean Endosperm

Abstract

The stability of catalase, fumarase and isocitrate lyase from deliberately broken organelles in crude extracts from endosperm tissue of castor bean seedlings was examined. These enzymes are relatively stable at 2.degree. C in extracts from endosperm of 2 day seedlings but rapid losses of activity occur in extracts from older seedlings. These losses are caused by the thiol-proteinase present in the extracts. The inclusion of 35% glycerol prevented the loss of catalase, fumarase and isocitrate lyase activity and various inhibitors of proteinases afforded limited protection. The most striking protectant was leupeptin, an inhibitor of serine and thiol-proteinases. Leupeptin completely inhibited the loss of activity of the 3 enzymes in crude extracts and improved yields when included in the grinding medium.