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

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 lM 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 Ki is found to be 4 lM for Li2SO4, and
1 lM 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.