PURIFICATION AND PROPERTIES OF EMODIN DEOXYGENASE FROM PYRENOCHAETA TERRESTRIS

Article abstract of DOI:10.1016/0031-9422(90)85158-C

Emodin deoxygenase, which catalyses the reduction of emodin to chrysophanol, was purified 17-fold from crude extracts of Pyrenochaeta terrestris.The M_r of the enzyme was 103000.Upward curvature was exhibited by the plot of rate vs concentration of the crude extract.The protein fraction obtained from gel filtration with Sephadex G-75 was activated by ATP plus a low M_r fraction; ATP alone or low M_r fraction alone did not increase its activity.The K_m for NADPH of the crude extract was 3 μM, that after NADPH gel filtration of the crude extract was 1.5 mM.It is proposed that ATP plus an unidentified factor increase emodin deoxygenase activity by lowering the K_m for NADPH.Iron II, which increased activity of the crude extract, inhibited activity of the partially purified enzyme by 95 percent.Sulphydryl reagents inhibited activity by 90 percent.Partially purified emodin deoxygenase activity was low in the absence of mercaptans and was increased eight-fold by the addition of dithiothreitol.It is proposed that a pair of thiol groups is required for activity and that they occur in the disulphide form in the absence of mercaptans.