ACTIVITIES OF PHOSPHOMONOESTERASE AND PHOSPHODIESTERASE FROM LUMBRICUS-TERRESTRIS

Abstract

The relationship between enzymes that can hydrolyze p-nitrophenylphosphate and bis[p-nitrophenyl] phosphate from the earthworm Lumbricus terrestris was investigated. In contrast to what occurs with most alkaline phosphatases from other species, the hydrolysis of both substrates was significantly inhibited by dithiothreitol, but not by the thiol-directed inhibitors iodoacetamide and p-chloromercuribenzenesulfonic acid, suggesting that a sulfhydryl group is not directly involved in catalysis. The enzymes were inhibited by Zn, but not significantly affected by Mg. The enzymes were activated by Ca and addition of EDTA to incubations in the absence of exogenously added Ca slightly decreased activity. The presence of the organophosphate trichlorfon did not result in reduced activity with either substrate, suggesting that the active sites for the phosphoesterases may not be involved in the hydrolysis of aliphatic organophosphates and that cholinesterase is not involved in the hydrolysis of these substrates. Gel filtration revealed two peaks of alkaline phosphatase activity at 230 and 40 kDa. The major fraction of phosphodiesterase activity was associated with the peak at 230 kDa. The peak at 40 kDa was incapable of hydrolyzing bis[p-nitrophenyl] phosphate, suggesting the presence of at least two alkaline phosphatase isoenzymes in Lumbricus terrestris.