Partial purification and characterisation of cysteine protease in wheat germ.

Proteases have become an essential part of the modern food and feed industry, being incorporated in a large and diversified range of products for human and animal consumption. The objective of this study was to purify and characterise a protease from wheat germ. After purification a single protease of molecular weight 61-63 kDa (determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis) was obtained. The purified protease had optimal activity at 50 °C and maintained its activity completely after incubation at 30 °C for 30 min, while over 47% of the activity was lost after incubation at 80 °C for 30 min. The purified protease had optimal activity and maintained maximum stability at pH 5.5, while the activity decreased after incubation for 30 min at other pH values. The protease was inhibited by Mg(2+), Mn(2+), Ba(2+) and iodoacetic acid and stimulated by Li(+), Ca(2+), Cu(2+), β-mercaptoethanol and dithiothreitol, while Zn(2+), L-cysteine and glutathione had no significant effect on its activity. At pH 5.5 the enzyme had a K(m) of 0.562 mg mL(-1) with casein as substrate and showed higher affinity to casein than to bovine serum albumin, ovalbumin and gelatin. The purified enzyme from wheat germ was identified as a cysteine protease.