Purification and characterization of proteolytic enzymes from normal and opaque-2 Zea mays L. developing endosperms.

ABSTRACT

Purification and characterization of proteases from developing normal maize endosperm and high lysine opaque-2 maize endosperm have been carried out with a view to understand their role in storage protein modification. At day 15, normal maize endosperm had two types of proteolytic enzymes, namely, protease I and protease II, while at day 25 protease II disappeared and in place protease III appeared. However, in opaque-2 maize endosperm at both the stages only one type of enzyme (protease I) was present. These proteases had many properties in common—optimum pH and temperature were respectively, 5·7and 40°C; their activity was inhibited to the extent of 75 –93 % by p-chloromercuribenzoate; trypsin inhibitor inhibited the activity more at early stages of endosperm development; all proteases cleaved synthetic substrates p-tosyl-L-arginine methylesler and N-benzoyl-Ltyrosine ethyl ester and poly-L-glutamic acid. The Km values of day 15 and 25 normal maize endosperm proteases ranged from 2·73–3·30, while for opaque-2 maize endosperm protease I it was 3·33 mg azocasein per ml assay medium. These enzymes, however, differed with respect to proteolytic activity towards poly-L-lysine. Only normal maize endosperm protease III at day 25 followed by protease II at day 15 showed high activity towards this homopolypeptide suggesting thereby their role in determining the quality of normal maize endosperm protein.