Thiomorpholine and morpholine oxidation by a cytochrome P450 in Mycobacterium aurum MO1. Evidence of the intermediates by in situ H-1 NMR

Spectrophotometric assays of Mycobacterium aurum MO1 cells extracts gave ev idence of a soluble cytochrome P450, involved in the degradative pathway of morpholine, a waste product from the chemical industry. In order to get fu rther information, the kinetics of the biodegradation of the sulfur analogu e thiomorpholine was monitored by using in situ nuclear magnetic resonance (NMR). This technique allowed the identification of two intermediates: the sulfoxide of thiomorpholine resulting from S-oxidation and thiodiglycolic a cid owing to ring cleavage. The S-oxidation (S --> SO) represents one of th e well-known reactions catalyzed by cytochromes P450. The inhibitory effect of metyrapone, a cytochrome P450 inhibitor, on the thiomorpholine and morp holine degradative abilities of M. aurum MO1 confirmed the involvement of a cytochrome P450. These results and the decrease of the rate of formation o f the first intermediate during the morpholine degradation, 2-(2-aminoethox y) acetate, proved the key role of the cytochrome P450 in the early events of the biodegradation, i.e, in the C-N bond cleavage.