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①目的确定Ｌ－亮氨酸（Ｌ－Ｌｅｕ）对人类胎盘碱性磷酸酶（ＰＬＡＰ）的抑制类型，并探讨其抑制机理。②方法应用分光光度法分别测定有Ｌ－Ｌｅｕ和无Ｌ－Ｌｅｕ存在下的酶活力，根据其活力变化求出酶的相对活力；用双倒数作图法，确定Ｌ－Ｌｅｕ对ＰＬＡＰ的抑制类型并求出其抑制常数（Ｋｉ）；同时也观察了ｐＨ对抑制作用的影响。③结果Ｌ－Ｌｅｕ对ＰＬＡＰ有明显地抑制作用，抑制程度与ｐＨ有关；双倒数作图得到一组平行线，Ｋｉ为１．９８ｍｍｏｌ／Ｌ．④结论Ｌ－Ｌｅｕ是ＰＬＡＰ的反竞争性抑制剂，其抑制作用受ｐＨ的影响
Objective To determine the inhibitory effect of L-Leu on human placental alkaline phosphatase (PLAP) and its mechanism of inhibition. Methods The enzyme activities of L-Leu and L-Leu in the presence of L-Leu and L-Leu were determined by spectrophotometry. The relative activity of the enzyme was calculated according to the change of vitality. The inhibition constants (Ki) were calculated. The effect of pH on the inhibition was also observed. ③ Results L-Leu significantly inhibited PLAP, and the degree of inhibition was related to pH. The double-reciprocal plot showed a set of parallel lines with a Ki of 1.98 mmol / L. ④ Conclusion L-Leu is an anti-competitive inhibitor of PLAP and its inhibitory effect is affected by pH