ESTERASE ISOZYMES OF DROSOPHILA VIRILIS: PURIFICATION AND PROPERTIES OF α- AND β-ESTERASE ISOZYMES

Thirteen electrophoretic variants of esterases in Drosophila virilis, 9 of which controlled by Esterase-α locus and the others by Esterase-β locus respectively, have been partially purified and characterized biochemically. Enzymes purified by column chromatographic techniques from each stock were free from all other esterases on agar gel electrophoresis but contained a little amount of other proteins. α-esterase utilized both of α- and β-naphthyl acetates at the same extent, while β-esterase did not utilized the α-substrate. Both esterases were more strongly inhibited by DFP than by eserine. PCMB inhibited greatly the activity of α-esterase (80.1% by 10-4M) but not that of β-esterase (7.6% by 10-4M). EDTA did not have any effect on either of α- and β-esterases. The inhibition by PCMB of α-esterase was in part due to the action on -SH group involved in the active center. Generally speaking, the optimal pH of α-esterase was slightly lower than that of β esterase. β-esterase was more unstable than α-esterase by the heat treatment at 60°C. Molecular weight of α-esterase was estimated as 75, 000 and that of β-esterase was as 140, 000 by method of Sephadex gel filtration. Isoallelic variants of the esterases were very similar, there being no significant difference among them in substrate specificity and in molecular weight. However, there were differences in inhibition rates by DFP and PCMB, in optimal pH and in resistibility to treatment at 60°C.