METALLOPORPHYRIN CHELATASE FROM BARLEY

1. 1. A soluble enzyme which catalyzes the insertion of both zinc and iron into porphyrins has been prepared from etiolated barley seedlings. Purification of about 30-fold has been achieved by (NH4)2SO4 fractionation and chromatography on Sephadex G-150. Both zinc-chelatase and ferrochelatase activity fractionated in a parallel manner during all steps of purification. 2. 2. A simple and rapid procedure for determination of zinc-chelatase activity is described. This is based on fluorimetric determination of the rate of formation of zinc protoporphyrin. 3. 3. Evidence both favorable and opposed to the view that a single enzyme is involved in both iron- and zinc-chelatase action is discussed. Ferrochelatase activity was stimulated by preincubation with glutathione and dithiothreitol and was inhibited by p-chloromercuribenzoate and iodoacetamide. Zinc chelatase activity was stimulated by ATP and was relatively insensitive to air. Both activities had the same pH-activity curve, and Fe2+ competitively inhibited zinc-chelatase activity. © 1969.