Degradation of Rutin by Aspergillus flavus STUDIES WITH OXYGEN 18 ON THE ACTION OF A DIOXYGENASE ON QUERCETIN

Abstract The enzymatic oxygenation and cleavage of quercetin by quercetinase, an oxygenase produced by Aspergillus flavus, yield carbon monoxide and a depside, 2-protocatechuoyl-phloroglucinolcarboxylic acid. The enzyme does not incorporate oxygen from 18O2 into carbon monoxide, but incorporates both atoms of 18O2 into the depside. One atom of 18O2 is incorporated into the carboxyl group and the other into the ester carbonyl; thus quercetinase is a dioxygenase. Oxygen from H218O is not incorporated into either the depside or carbon monoxide. Both the carbon and oxygen of carbon monoxide are derived from the hydroxylated carbon 3 of quercetin. The reaction probably involves a direct and concerted addition of "activated oxygen" to quercetin at positions 2 and 4 to form an unstable cyclic peroxide intermediate which rapidly decomposes to give the products