MYROSINASE FROM ROOTS OF RAPHANUS-SATIVUS

Two myrosinase isoenzymes (EC 3.2.3.1) were extracted and purified by (NH4)(2)SO4 precipitation and DEAE-cellulose and Sephadex G-200 chromatography from radish root tissues with M(r)s 28 800 and 58 900. The most active one (120 U mg(-1)) was identified and characterized. The yield of the purified myrosinases was 21 mg (2398 U) of pure enzymes from 100 g of dry root tissues. The purity was ascertained by obtaining a single sharp band by disc electrophoresis. Optimal myrosinase activity on sinigrin was recorded in phosphate buffer, pH 6-6.5 at 37 degrees. The K-m for myrosinase with sinigrin as substrate was 0.47 mM at pH 6. The enzyme was stable for 45 min at 30 and 40 degrees (18% denaturation).