Degradation of rutin by Aspergillus flavus. Purification of the dioxygenase, quercetinase

Abstract

Evidence is presented that a single enzyme, quercetinase, is responsible for the degradation of quercetin by Aspergillus flavus to yield carbon monoxide and a depside, 2-protocatechuoylphloroglucinol carboxylic acid. A procedure for the isolation of the dioxygenase as a homogeneous protein is described. The most purified preparation degraded 10 800 μmoles of quercetin/h mg protein and was homogeneous as judged by ultracentrifugation and by electrophoresis. The molecular weight was determined as 111 000 + 4000. K_m values for quercetin and oxygen as substrates were 5.2 × 10⁻⁶ M and 1.2 × 10⁻⁴ M respectively. The enzyme is a glycoprotein containing 27.5% carbohydrate and the amino acid composition is presented.