Acid Carboxypeptidases in Grains and Leaves of Wheat, Triticum aestivum L.

Extracts of resting and germinating (3 days at 20 degrees C) wheat (Triticum aestivum L. cv Ruso) grains rapidly hydrolyzed various benzyloxycarbonyldipeptides (Z-dipeptides) at pH 4 to 6. Similar activities were present in extracts of mature flag leaves. Fractionation by chromatography on CM-cellulose and on Sephadex G-200 showed that the activities in germinating grains were due to five acid carboxypeptidases with different and complementary substrate specificities. The wheat enzymes appeared to correspond to the five acid carboxypeptidases present in germinating barley (L Mikola 1983 Biochim Biophys Acta 747: 241-252). The enzymes were designated wheat carboxypeptidases I to V and their best or most characteristic substrates and approximate molecular weights were: I, Z-Phe-Ala, 120,000; II, Z-Ala-Arg, 120,000; III, Z-Ala-Phe, 40,000; IV, Z-Pro-Ala, 165,000; and V, Z-Pro-Ala, 150,000. Resting grains contained carboxypeptidase II as a series of three isoenzymes and low activities of carboxypeptidases IV and V. During germination the activity of carboxypeptidase II decreased, those of carboxypeptidases IV and V increased, and high activities of carboxypeptidases I and III appeared. The flag leaves contained high activity of carboxypeptidase I and lower activities of carboxypeptidases II, IV, and V, whereas carboxypeptidase III was absent.