The structure functional catalytic activity of rice bran lipase in the presence of selenium and lithium

Abstract

Rice bran lipase (RBL), an esterase (EC 3.1.1.3) is a versatile enzyme that catalyzes the hydrolysis of ester linkages, primarily in neutral lipids, such as triglycerides. The catalytic activity of RBL in the presence of selenium and lithium has been investigated. Lipase isolated from rice bran was treated with different concentrations of selenium and lithium ions and further subjected to activity determination, along with the kinetics of inhibition of RBL in conjunction with structure–function relationship of the enzyme. Both ions showed competitive inhibition of RBL activity in a concentration-dependent manner (1 μM to 1 mM). At 1 mM concentration of SeO₂ and Li₂SO₄, the enzyme loses its activity by 78 and 71%, respectively. From the analysis of the kinetic data, the inhibition constant K _i is found to be 4 μM for Li₂SO₄, and 1 μM for SeO₂, respectively. Spectrofluorimeter analysis and far UV-CD data showed minor changes in the emission intensity and conformation of the RBL in the presence of these ions at the above concentration. The results suggest that both selenium and lithium specifically inhibit RBL by probably binding near to the catalytic site or distorting the geometry of the active site of the RBL triad.