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

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 34Uminmgof 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, Ag, Hg, 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.