Influence of zinc and cobalt on expression and activity of parathion hydrolase from Flavobacterium sp. ATCC27551

Organophosphorus triesterases are encoded by the organophosphate degradation (opd) gene found in species of Flavobacterium, Pseudomonas, and Agrobacterium. They are involved in hydrolysis of triester bonds found in a variety of organophosphorus pesticides. In view of their potential biotechnological importance in disposal of pesticide wastes, several attempts have been made to express the opd gene in heterologous hosts. Increased levels of parathion hydrolase (PH) activity were previously reported in the presence of divalent metal ions such as zinc and cobalt, and it was suggested that this reflected metal ion-induced transcriptional activation of opd. We have now used opd-lacZ fusions to examine the influence of zinc and cobalt on opd expression, and found no effects. However, when opd was expressed from the lac promoter there was considerable increase in PH activity if the culture medium was supplemented with 1 mM zinc or cobalt although the amount of PH was unaffected. These results suggest that the increase in specific activity of PH caused by these divalent cations is due to improved folding of overexpressed protein.