title: NADH-dependent glutamate synthase from lupin nodules. Reactions with oxidised and reduced 3-acetylpyridine-adenine dinucleotide.
abstract: 3-Acetylpyridine-adenine dinucleotide, reduced form (AcPdADH) is able to act as an alternative reductant in glutamate-synthase-catalysed glutamate synthesis. In the AcPdADH-dependent reaction, kcat and Km values for the other substrates are fourfold lower than those for the NADH-dependent reaction, and Km for AcPdADH is about 3 microM. AcPdADH acts as a competitive inhibitor with respect to NADH in NADH-dependent glutamate synthesis, with a Ki of 1 microM. Glutamate synthase catalyses NADH-dependent reduction of AcPdAD+. This appears to proceed by a substituted-enzyme (ping-pong) mechanism, with competitive substrate inhibition by NADH at high levels. The Km values for this reaction are 1.4 microM for NADH and 14 microM for AcPdAD+ and kcat is 51 s-1; Ki for NADH is about 10 microM. The latter findings suggest that NADH is capable of reducing the enzyme molecule in the absence of other substrates and that a reduced form of the enzyme can exist in the absence of bound NADH.
mesh_terms: D003067:Coenzymes / Q000494:pharmacology*; D005970:Glutamate Synthase / Q000378:metabolism*; D007700:Kinetics; D009243:NAD / Q000031:analogs & derivatives* / Q000494:pharmacology; D010084:Oxidation-Reduction; D010944:Plants / Q000201:enzymology*; D013056:Spectrophotometry, Ultraviolet; D000637:Transaminases / Q000378:metabolism*
chemical_list: D003067:Coenzymes; D009243:NAD; C005941:3-acetylpyridine adenine dinucleotide; D005970:Glutamate Synthase; D000637:Transaminases