Pepstatin-sensitive proteolytic activity of sorghum seeds

Two novel proteinases were isolated from resting sorghum seeds and purified 100-fold. The activity of the purified enzymes was completely inhibited by pepstatin A and was unaffected by PMSF, leupeptin, EDTA and E-64 (L-trans- epoxysuccinyl leucylamino 4 guanidino butane), which indicates that they b elong to the class of aspartic proteinases. SDS-PAGE and native-PAGE reveal ed a monomeric 29-kDa enzyme and a heterodimeric 61-kDa enzyme with two S-S linked subunits of 49 and 12 kDa. The proteases have maximum activity at 4 5 degrees C and pH 3.5, with haemoglobin as substrate. Activity at 60 degre es C is higher than at 30 degrees C.