Characterization of Pepstatin-Sensitive Acid Protease in Resting Rice Seeds

抄録

Resting rice seeds contained an acid protease whose optimal pH was 3.5 for casein containing 3.6_M urea and 2.5_??_3.0 for acid denatured haemoglobin. The enzyme was stable in a pH range between 5 and 9. The apparent molecular weight of the enzyme was 60000_??_65000. The enzyme was separated into several fractions by ion-exchange chromatography on DE-32 and by isoelectric focusing. Multiple forms of the enzyme were assumed to be due to the complex formation of the enzyme and inactive proteins. The enzyme activity was completely inhibited by 1×10^-6_M pepstatin. ID₅₀ value of the enzyme for pepstatin was estimated to be 5×10^-8_M, which indicates a high affinity of the enzyme for pepstatin. The enzyme is a typical acid protease (carboxyl proteinase) that is sensitive to pepstatin.