Mechanisms of Steroid Oxidation by Microorganisms IX. OK THE MECHANS?\I OF RIKG A CLEAVAGE IN THE DEGRADATION OP 9,10-SEC0 STEROIDS BY MICROORGAKIS?1IS*

Cell extracts, prepared from Nocardia restrictus, rapidly oxidize 3,4-dihydroxy-9,lO-secoandrosta-l,3,5(10)-triene9,17-dione with the consumption of 1 mole of oxygen per mole of substrate; no carbon dioxide is evolved. The reaction is stimulated by the presence of ferrous ions. The first product of ring fission has been identified as 4(5),9(10)-diseco-3 -hydroxyandrosta-l(lO),Z-diene-5,9,17trion-4-oic acid. The enzyme catalyzing the formation of this compound has been tentatively termed 3,4-dihydroxy9,10-secoandrosta-1,3,5(10)-triene-9,17-dione 4,5-dioxygenase. The possible role of a quinone intermediate in the formation of the ring fission compound has been eliminated. Further metabolism of the ring fission compound results in the formation of 2-oxo-4-hydroxycaproic acid (isolated as its y-lactone) and 3aa-H-4a-[3’-propionic acid]-7ap-methylhexahydro-1,5Gndanedione. Whole cells in the presence of 0.001 M arsenite cleave 2-oxo-4-hydroxycaproic acid to pyruvate and propionaldehyde. A reaction sequence has been proposed for the metabolism of 3,4-dihydroxy-9,lO-secoandrosta-1,3,5(10)-triene-9,17dione by N. restrictus.