Ullah A H
Southern Regional Research Laboratory, ARS, USDA, New Orleans, Louisiana 70124.
Prep Biochem. 1988;18(4):459-71. doi: 10.1080/00327488808062544.
Purified Aspergillus ficuum phytase's partial primary structure and amino acid and sugar composition were elucidated. Determination of kinetic parameters of the enzyme at different pH values and temperatures indicated no significant alteration of the Km for phytate while the Kcat was affected. The enzyme was able to release more than 51% of the total available Pi from phytate in a 3.0 hr assay at 58 degrees C, but the Kcat dropped to 15% of the initial rate. Substrate selectivity studies revealed phytate to be the preferred substrate. The pH optima of phytase was 5.0, 4.0, and 3.0 for phytate, ATP, and polyphosphate, respectively. The enzyme had varied sensitivity towards cations. While Ca++ and Fe++ produced no effect on the catalytic rate of the enzyme, Cu+, Cu++, Zn++, and Fe were found to be inhibitory. Mn++ was observed to enhance enzyme activity by 33% at 50 microM. Known inhibitors of acid phosphatases e.g. L (+)-tartrate, phosphomycin, and sodium fluoride had no effect on enzyme activity.
阐明了纯化的泡盛曲霉植酸酶的部分一级结构以及氨基酸和糖组成。在不同pH值和温度下测定该酶的动力学参数表明，肌醇六磷酸的米氏常数（Km）无显著变化，而催化常数（Kcat）受到影响。在58℃下进行3.0小时的测定中，该酶能够从肌醇六磷酸中释放出超过51%的总有效磷，但Kcat降至初始速率的15%。底物选择性研究表明肌醇六磷酸是首选底物。植酸酶对肌醇六磷酸、ATP和多聚磷酸的最适pH分别为5.0、4.0和3.0。该酶对阳离子的敏感性各不相同。虽然Ca++和Fe++对酶的催化速率没有影响，但发现Cu+、Cu++、Zn++和Fe具有抑制作用。观察到在50微摩尔时，Mn++可使酶活性提高33%。已知的酸性磷酸酶抑制剂，如L(+)-酒石酸、磷霉素和氟化钠对酶活性没有影响。
