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Regulatory Properties of the Flavoprotein l-Lysine Monooxygenase

1974; Elsevier BV; Volume: 249; Issue: 8 Linguagem: Inglês

10.1016/s0021-9258(19)42771-3

1083-351X

Marcia I.S. Flashner, Vincent Massey,

Photochemistry and Electron Transfer Studies

Abstract The steady state kinetic properties of l-lysine monooxygenase from Pseudomonas fluorescens have been investigated. The enzyme has been shown to exhibit both oxygenase and oxidase activity with different substrates, the oxidase activity being much less efficient. Lysine is an oxygenase-type substrate while ornithine is an oxidase-type substrate (Nakazawa, T., Hori, K. and Hayaishi, O. (1972) J. Biol. Chem. 247, 3439–3444). During steady state analysis, both substrates exhibit sigmoidal saturation curves. Hill plots for lysine and ornithine are biphasic, with the Hill coefficient n = 2.9 at low substrate concentrations and n = 1 at higher concentrations. With lysine as substrate, the reaction does not go to completion, and the per cent completion of the reaction is a function of the initial lysine concentration. e-Aminocaproic acid has been found to act as a nonsubstrate effector by permitting the reaction to reach completion. Furthermore, e-aminocaproate reduces the cooperative effect of lysine, converting the biphasic Hill plot to a monophasic one, with a Hill coefficient of 1 obtaining over most of the concentration range of lysine studied. e-Aminocaproate is also a competitive inhibitor toward lysine with a Ki of 2.6 x 10-4 m. e-N,N-Dimethyl-l-lysine is a poor substrate except in the presence of lysine, in which case the reaction proceeds with both substrates, but stops short of completion, as seen with lysine alone as substrate. These results indicate that lysine itself is an effector, and that at least two sites per flavin are important to catalysis, i.e. one catalytic site and one or more effector sites.