β-GALACTOSIDASE FROM WATERMELON (Citrullus lanatus) SEEDLINGS: PARTIAL PURIFICATION AND PROPERTIES

Abstract

β-Galactosidase from watermelon (Citrullus lanatus) seedlings was partially purified. Extract was fractionated in two steps with ammonium sulfate at 30 & 80% saturations. Ammonium sulfate precipitated enzyme yielded 60% recovery and two folds purification of the enzyme. Further, the enzyme was subjected to CM-Cellulose and Sephadex G-100 chromatography to obtain 24-folds purification. The specific activity was increased to from 1.5 U to 36 U per milligram of protein. The overall yield was 13.2%. The enzyme had optimum pH 4.8 and pH stability between pH 4.0 and 7.0 was observed. Optimum temperature was 50°C and temperature stability was also shown up to 50°C. Thereafter enzyme activity fell and inactivated completely at 70°C. The Km and Vmax were found to be 0.2 mM and 34Umin-1mg-1of protein, respectively. β-mercaptoethanol exhibited very small activation at moderate concentration, but the inhibition was displayed at high concentrations. Heavy metal ions such as Al+3, Ag+1, Hg+2, etc. inhibited the enzyme strongly. The inhibition by heavy metals and SH-reacting reagents suggests that cystein was necessary for enzyme activity. On the addition of β-mercaptoethanol to pre-incubated enzyme with metal ions, the inhibition was relieved. The β-Galactosidase activity was increased in the presence of alcohols. This activation reflected glycosyltransferase activity.