Schachet M S, Squire P G
Int J Pept Protein Res. 1976;8(5):481-9. doi: 10.1111/j.1399-3011.1976.tb02528.x.
Michaelis-Menten kinetics are observed in studies of highly purified bovine adrenal glucose-6-phosphate dehydrogenase at pH8.0 in 0.1 M bicine. The Km for NADP+ is 3.8 muM and for glucose-6-phosphate, 61 muM. At pH 6.9 Km for NADP+ increases to 6.5 muM. The enzyme is inhibited by NADPH both at pH 6.8 and at 8.0 with a Kip of 2.36 muM at pH 8.0. Inhibition is competitive with respect to both substrates implying that addition of substrates is random ordered. The data are also interpreted in terms of "reducing charge", the mole fraction of coenzyme in the reduced form. This appears to be the major mechanism for regulation of the pentose shunt. D-glucose, oxidized by the enzyme at a very slow rate, is also a competitive inhibitor for the natural substrate with a Ki of 0.29 M. Phosphate is a competitive inhibitor for glucose-6-phosphate oxidation but both phosphate and sulfate accelerate glucose oxidation suggesting a common binding site for the two anions and the phosphate of the natural substrate. While binding of ACTH to our enzyme preparations has been observed, we have not been able, in spite of repeated attempts, to demonstrate augmentation of the activity of the enzyme by the addition of ACTH.
在对高度纯化的牛肾上腺葡萄糖-6-磷酸脱氢酶于pH8.0的0.1M 二乙醇胺缓冲液中的研究中观察到了米氏动力学。NADP⁺的米氏常数（Km）为3.8μM，葡萄糖-6-磷酸的Km为61μM。在pH6.9时，NADP⁺的Km增加到6.5μM。该酶在pH6.8和8.0时均受到NADPH的抑制，在pH8.0时抑制常数（Kip）为2.36μM。抑制作用对两种底物而言都是竞争性的，这意味着底物的添加是随机有序的。这些数据也根据“还原电荷”（即辅酶以还原形式存在的摩尔分数）进行了解释。这似乎是戊糖磷酸途径调节的主要机制。D-葡萄糖被该酶氧化的速率非常慢，它也是天然底物的竞争性抑制剂，抑制常数（Ki）为0.29M。磷酸是葡萄糖-6-磷酸氧化的竞争性抑制剂，但磷酸和硫酸都能加速葡萄糖氧化，这表明这两种阴离子与天然底物的磷酸具有共同的结合位点。虽然已经观察到促肾上腺皮质激素（ACTH）与我们的酶制剂结合，但尽管反复尝试，我们仍未能证明添加ACTH会增强该酶的活性。
