PURIFICATION AND PROPERTIES OF AN ESTERASE FROM CUCURBITA MAXIMA FRUIT TISSUE

Article abstract of DOI:10.1016/0031-9422(89)80016-0

An esterase from the fruit of Cucurbita maxima was purified to apparent homogeneity.The enzyme displays an M_r, of 36 000, a pI value of 4.9, a Stokes radius of 2.70 nm, diffusion coefficient of 9.25 x 1E-7 cm²/sec, possesses a homogeneous dimeric quaternary structure with a subunit M_r of 18 000.High esterolytic activity was observed with indophenyl acetate (1510 μmol/min/mg protein and p-nitrophenyl acetate (648 μmol/min/mg protein) while the enzyme displayed no carboxypeptidase, amidase, proteinase or aminopeptidase activities.Based on indophenyl acetate as substrate, the esterase has an optimum pH of 7.5 to 8.9 and a K_M value.14 mM at pH 8.0.The esterolytic activity is strongly inhibited by mercaptide-forming and alkylating thiol reagents and by diisopropyl fluorophosphate and phenylmethylsulphonyl fluoride.Product inhibition by indophenyl was competitive (apparent K_i=90 μM) relative to indophenol acetate and parabolic.Acetate was without effect.Key Word Index - Cucurbita maxima; Cucurbitaceae; esterase.