Turner A C, Lushbaugh W B
Department of Preventive Medicine, University of Mississippi Medical Center, Jackson 39216-4505.
Exp Parasitol. 1988 Oct;67(1):47-53. doi: 10.1016/0014-4894(88)90007-0.
An NADP-linked glutamate dehydrogenase (EC 1.4.1.4) was found in the soluble fraction of Trichomonas vaginalis. Its molecular weight was about 230,000 (gel filtration). The enzyme, partially purified by diafiltration and hydroxyapatite column chromatography, was heat stable (1 hr at 57 C). It catalyzed both the amination of alpha-ketoglutarate (mean Km 0.6 mM) and the deamination of glutamate (mean Km 1.2 mM) The optimum pH of the amination reaction was 6.7, and that of the deamination reaction was 8. Glutamate was a competitive inhibitor of the amination reaction (mean Ki 5.6 mM) and alpha-ketoglutarate a partially competitive inhibitor of the deamination reaction (mean Ki 0.45 mM). Both guanosine and inosine diphosphates (1 mM) increased the Km alpha-ketoglutarate fivefold (mean Ki's 0.3 and 0.4 mM, respectively). Guanosine diphosphate reduced the Km glutamate 40%. Adenosine di- and triphosphate (1 mM) were ineffective. Because the amination reaction displayed substrate inhibition, guanosine and inosine diphosphates were potent natural inhibitors, and ammonia released by deamination reactions would tend to raise pH (amination operative at acid pH), we hypothesize that the deamination reaction may predominate in the living organism.
在阴道毛滴虫的可溶性部分发现了一种与NADP相关的谷氨酸脱氢酶（EC 1.4.1.4）。其分子量约为230,000（凝胶过滤法）。通过透析过滤和羟基磷灰石柱色谱法部分纯化的该酶具有热稳定性（57℃下1小时）。它催化α-酮戊二酸的胺化反应（平均Km为0.6 mM）和谷氨酸的脱氨反应（平均Km为1.2 mM）。胺化反应的最适pH为6.7，脱氨反应的最适pH为8。谷氨酸是胺化反应的竞争性抑制剂（平均Ki为5.6 mM），α-酮戊二酸是脱氨反应的部分竞争性抑制剂（平均Ki为0.45 mM）。鸟苷二磷酸和肌苷二磷酸（1 mM）均可使α-酮戊二酸的Km增加五倍（平均Ki分别为0.3和0.4 mM）。鸟苷二磷酸可使谷氨酸的Km降低40%。腺苷二磷酸和三磷酸（1 mM）则无作用。由于胺化反应表现出底物抑制作用，鸟苷二磷酸和肌苷二磷酸是有效的天然抑制剂，且脱氨反应释放的氨会使pH升高（胺化反应在酸性pH下进行），我们推测脱氨反应在活生物体中可能占主导地位。
