STUDIES ON THE in vitro O2‐DEPENDENT INACTIVATION OF NADH‐GLUTAMATE SYNTHASE FROM Chlamydomonas reinhardii STIMULATED BY FLAVINS

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Abstract
The NADH‐glutamate synthase (EC 1.4.1.14) complex fromChlamydomonas reinhardiimay experiencein vitrotwo kinds of 02‐dependent inactivation stimulated by flavins.A peroxide‐mediated inactivation of enzyme, which affects the NADH‐ and MVt‐glutamate synthase activities of the complex, but not the NADH‐dehydrogenase activity, can be obtained by aerobic incubation of the enzyme with NAD(P)H plus flavin. This inactivation of enzyme seems to be due to a permanent modification of sulfhydryl groups near the active site for L‐glutamine or 2‐oxoglutarate. The addition of 10 mM dithioerythritol to inactive NADH‐glutamate synthase produces a significant, but not complete, reactivation of the enzyme.On the other hand, the NADH‐glutamate synthase is highly susceptible to a photodynamic inactivation caused by singlet02.Aerobic incubation of the active enzyme with flavin under illumination leads to the irreversible inactivation of all the activities associated with the enzymatic complex.
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