Boland M J
Eur J Biochem. 1981 Apr;115(3):485-9.
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.
3-乙酰吡啶腺嘌呤二核苷酸还原型（AcPdADH）能够在谷氨酸合酶催化的谷氨酸合成中作为替代还原剂。在依赖AcPdADH的反应中，其他底物的kcat和Km值比依赖NADH的反应低四倍，并且AcPdADH的Km约为3 microM。在依赖NADH的谷氨酸合成中，AcPdADH相对于NADH起竞争性抑制剂的作用，Ki为1 microM。谷氨酸合酶催化NADH依赖的AcPdAD +还原。这似乎通过取代酶（乒乓）机制进行，在高水平时NADH具有竞争性底物抑制作用。该反应的Km值对于NADH为1.4 microM，对于AcPdAD +为14 microM，kcat为51 s-1；NADH的Ki约为10 microM。后一个发现表明，在没有其他底物的情况下，NADH能够还原酶分子，并且在没有结合NADH的情况下可以存在还原形式的酶。
