大鼠垂体提取物中至少两种甲基转移酶催化磷脂酰乙醇胺合成磷脂酰胆碱。

Synthesis of phosphatidylcholine from phosphatidylethanolamine by at least two methyltransferases in rat pituitary extracts.

作者信息

Prasad C, Edwards R M

出版信息

J Biol Chem. 1981 Dec 25;256(24):1300-3.

Abstract

Rat pituitary extracts contain at least two methyltransferases that methylate phosphatidylethanolamine to phosphatidylcholine using S-adenosylmethionine as the methyl donor. The first enzyme methylates phosphatidylethanolamine to phosphatidyl-N-monomethylethanolamine and has a high Km (40-42 microM) for S-adenosylmethionine, whereas the second enzyme(s) catalyzes two successive methylations of phosphatidyl-N-monomethylethanolamine to phosphatidyl-N,N-dimethylethanolamine and then to phosphatidylcholine and has a low Km (6.7 microM) for S-adenyl-L-methionine. The first enzyme is loosely bound to the membrane fraction; therefore it appears in both particulate (20,000 X g) and supernatant (20,000 X g) fractions, whereas the second enzyme(s) is tightly bound to the membrane and thus appears only in the particulate fraction. Both methyltransferases have two pH optima of 6.5 and 9.5 (9.5 activity greater than 6.5 activity) and they do not require Mg2+.

摘要

大鼠垂体提取物含有至少两种甲基转移酶，它们以S-腺苷甲硫氨酸作为甲基供体，将磷脂酰乙醇胺甲基化为磷脂酰胆碱。第一种酶将磷脂酰乙醇胺甲基化为磷脂酰-N-单甲基乙醇胺，对S-腺苷甲硫氨酸具有较高的Km值（40 - 42微摩尔），而第二种酶催化磷脂酰-N-单甲基乙醇胺连续两次甲基化，先形成磷脂酰-N,N-二甲基乙醇胺，然后再形成磷脂酰胆碱，对S-腺苷-L-甲硫氨酸具有较低的Km值（6.7微摩尔）。第一种酶与膜部分结合松散；因此它同时出现在颗粒部分（20,000×g）和上清部分（20,000×g）中，而第二种酶与膜紧密结合，因此仅出现在颗粒部分。两种甲基转移酶都有两个pH最适值，分别为6.5和9.5（9.5时的活性大于6.5时的活性），并且它们不需要Mg2+。