Sherman W R, Rasheed A, Mauck L A, Wiecko J
J Biol Chem. 1977 Aug 25;252(16):5672-6.
myo-Inositol-1-P synthase (EC 5.5.1.4) purified from rat testis and from bovine testis was allowed to react with D-[5-18O]glucose-6-P. myo-Inositol, obtained in these reactions, retained all of the 18O originally in the glucose-6-P. When these enzyme preparations were incubated with unlabeled glucose-6-P in a medium enriched in H2 18O no uptake of the oxygen isotope occurred that could be ascribed to the myo-inositol-1-P synthase reaction. By these criteria this enzyme, which is considered to use an aldolase mechanism in the cyclization step, cannot form a Schiff base during the reaction. In addition, these enzymes are not inhibited by 10 mM EDTA. One interpretation of this evidence is that the myo-inositol-1-P synthases we have studied are neither Class I nor Class II aldolases, and simply use base catalysis in the cyclization step.
从大鼠睾丸和牛睾丸中纯化得到的肌醇-1-磷酸合酶（EC 5.5.1.4），使其与D-[5-¹⁸O]葡萄糖-6-磷酸发生反应。在这些反应中获得的肌醇保留了葡萄糖-6-磷酸中最初所有的¹⁸O。当将这些酶制剂与未标记的葡萄糖-6-磷酸在富含H₂¹⁸O的培养基中孵育时，未发生可归因于肌醇-1-磷酸合酶反应的氧同位素摄取。根据这些标准，这种在环化步骤中被认为采用醛缩酶机制的酶，在反应过程中不会形成席夫碱。此外，这些酶不受10 mM EDTA的抑制。对这一证据的一种解释是，我们所研究的肌醇-1-磷酸合酶既不是I类醛缩酶也不是II类醛缩酶，而只是在环化步骤中使用碱催化。
