Characterization of Esterases of Tamarindus indica Seeds

Germinating seeds of Tamarindus indica synthesizes various enzymes which are required for the degradation of seed reserves such as xyloglucans, fatty acid esters and proteins. Among these, esterases, belonging to a group of hydrolytic enzymes catalyze the hydrolysis of various types of esters. They play an important role in cell expansion as well as detoxification of xenobiotics and many agrochemicals and insecticides. The esterases are extracted from the germinating tamarind seeds using 50 mM phosphate buffer, pH 7. The Km with α-naphthyl acetate as the substrate is 19.23 μM and the enzymes are optimally active at pH 7.0 to 7.5 and are stable between pH 5.0 to 9.0. The optimum temperature of esterase activity of tamarind seed is between 37 ̊C 50 ̊C and is stable up to 40 ̊C. The activity declined by 30% at 60 ̊C and about 90% at 70 ̊C. Highest esterase activity and specific activity are observed on the 21st day of germination. The polyacrylamide gel electrophoresis (PAGE) indicated the presence of nine isozymes of esterases. Band numbers 1, 5 and 6 are the major esterolytic bands present throughout the germination period while band numbers 2 & 3 are minor bands present only during the latter period of the germination. Based on substrate and inhibitor specificity in conjunction with electrophoresis, the esterases 1 to 8 have been classified as carboxylesterases sensitive to organophosphate inhibitor (OP) and PCMB (p-chloromercuribenzoate) while esterase 9 is classified as carboxylesterase sensitive to OP. These esterases are unaffected by carbamate inhibitor, eserine sulphate.