GLYCOSIDASES OF TURNIP LEAF TISSUES .1. PHYSIOCHEMICAL PROPERTIES OF MYROSINASE AND DISACCHARASE ENZYMES

Four myrosinase (beta-thioglucosidase EC. 3.2.3.1) and seven disacchar ase (beta-fructofuranosidase, EC. 3.2.1.26) isoenzymes were isolated f rom turnip leaves. The most active enzymes were isolated in pure form. Myrosinase and disaccharase mol wt was 62.0 x 10(3) and 69.5 x 10(3) dalton, respectively, on the basis of gel filtration on Sephadex G-200 . Myrosinase pH profile showed high activity between pH 5 and 7 with t he optimum at pH 5.5. The purified enzyme was heat-stable for 60 min a t 30 degrees C with only loss of 24% of activity. Its activity is stro ngly inhibited (100%) by Pb2+, Ba2+, Cu2+, and Ca2+ ions, and activate d (70%) by EDTA at 0.04M. The pure enzyume failed to hydrolyze amylose , glycogen, lactose, maltose, and sucrose. The K-m and V-max values of myrosinase using sinigrin as specific substrate was 0.045 mM and 2.5 U, respectively. The maximal activity of disaccharase enzyme was obtai ned at pH 4-5 and at 35-37 degrees C. The enzyme was heat-stable at 30 degrees C for 30 min with only 10% loss of its activity. Its activity is strongly activated (70-240%) by Ca2+, Ba2+, Cu2+, and EDTA at 0.01 M. The enzyme activity is specific to the disaccharide sucrose and fai led to hydrolyze other disaccharides (maltose and lactose). The K-m an d V-max of disaccharase were 0.123 mM and 3.33 U, respectively.