2-COMPONENT FLAVIN-DEPENDENT PYRROLE-2-CARBOXYLATE MONOOXYGENASE FROMRHODOCOCCUS SP

Pyrrole-2-carboxylate can serve as the sole source of carbon, nitrogen , and energy for a strain tentatively identified to belong to the genu s Rhodococcus. An NADH-dependent oxygenase activity was detected in ce ll extracts that initiated the degradation of the substrate. During pu rification of the enzyme, this activity was separated into two protein components which were both purified to apparent homogeneity. A small monomeric 18.7-kDa protein designated as reductase, catalyzed in vitro the NADH and FAD-dependent reduction of cytochrome c and had an NADH- oxidase activity. The second component, a 54-kDa protein with a trimer ic native structure had no enzymatic activity by itself, but exhibited a pyrrole-2-carboxylate-dependent oxygen consumption when it was comp lemented with the reductase component, FAD, acid NADH. This indicated that the large protein referred to as oxygenase was responsible for th e oxygen-dependent hydroxylation of the substrate. The rate of an unco upled NADH oxidation without hydroxylation of the substrate was found to be strongly dependent on the molar ratio of both components. The un coupling was nearly completely suppressed by a 5-7-fold molar excess o f the oxygenase component. The small protein was N-terminally blocked. It was thus proteolytically digested and four of the resulting peptid es were sequenced comprising 47 amino acids. The sequences of these fr agments were similar to the sequences reported for the small component of different two-component flavin monooxygenases. Furthermore, the N- terminus of the oxygenase component showed high sequence similarity to the second, usually large subunit of these enzymes and to two single- component flavin monooxygenases. Thus, the enzyme from Rhodococcus sp. designated as pyrrole-2-carboxylate monooxygenase belongs to the rece ntly discovered new class of two-component flavin aromatic monooxygena ses. Some of the basic properties of both components were determined a nd their interaction during catalysis was investigated.