Sastry B V, Janson V E
Biochem Pharmacol. 1983 Apr 15;32(8):1423-32. doi: 10.1016/0006-2952(83)90457-4.
Alteration of membrane fluidity during enzymatic methylation of membrane phosphatidyl-ethanolamine (PE) and neutralization of negative charges of membrane proteins due to methylation of carboxyl groups may contribute to sperm motility. Therefore, enzymatic phospholipid methylation and carboxymethylation, and the consequences of their inhibition on motility, were studied using human sperm. These studies gave the following results. Human sperm homoganates contained two phospholipid N-methyltransferases (PMT) which converted PE to phosphatidylcholine (PC) in the presence of S-adenosylmethionine (SAM). The first PMT converted PE to phosphatidyl-N-methylethanolamine (PME). In had a Km of 4.0 microM and a pH optimum of 8.0. The second PMT converted PME to phosphatidyl-N,N-dimethylethanolamine and PC. It had a Km of 71 microM and a pH optimum of 10.0. Spermatozoa also contained protein carboxymethylase (PCM) and methyl aceptor protein (MAP). The intracellular levels of S-adenosylhomocysteine (SAH), an inhibitor of SAM-mediated methylations, were increased by adding adenosine (100 microM), L-homocysteine thiolactone (L-HCT, 10 microM), and erythro-9-(2-hydroxy-3-nonyl)-adenine (EHNA, 10 microM), an inhibitor of adenosine deaminase, to human sperm ejaculates that had been diluted with sodium phosphate buffer at pH 7.4 and 25 degrees. The motility index of each sperm suspension was determined every hour for 4 hr. In the presence of the mixture of adenosine, L-HCT and EHNA, the motility index was depressed by 57%. Under similar conditions, phospholipid methylation was depressed by 48%. Similar experiments were also conducted in the presence of 3-deazaadenosine (Deaza, 80 microM), a selective inhibitor of SAH hydrolase. In the presence of adenosine and L-HCT, Deaza depressed the motility index by 60% and phospholipid methylation by 86%. The potencies of SAH in the inhibition of phospholipid methylation and protein carboxymethylation in sperm homogenates had the following order: PMT I greater than PCM greater than PMT II. These observations indicate that the PMT system and/or the PCM-MAP system play a significant role in the regulation of human sperm motility.
膜磷脂酰乙醇胺（PE）的酶促甲基化过程中膜流动性的改变以及由于羧基甲基化导致膜蛋白负电荷的中和可能有助于精子的运动。因此，使用人类精子研究了酶促磷脂甲基化和羧甲基化及其对运动抑制的后果。这些研究得出了以下结果。人类精子匀浆含有两种磷脂N-甲基转移酶（PMT），它们在S-腺苷甲硫氨酸（SAM）存在下将PE转化为磷脂酰胆碱（PC）。第一种PMT将PE转化为磷脂酰-N-甲乙醇胺（PME）。其Km为4.0微摩尔，最适pH为8.0。第二种PMT将PME转化为磷脂酰-N，N-二甲乙醇胺和PC。其Km为71微摩尔，最适pH为10.0。精子还含有蛋白质羧甲基酶（PCM）和甲基受体蛋白（MAP）。通过向已用pH 7.4和25℃的磷酸钠缓冲液稀释的人类精子射精中添加腺苷（100微摩尔）、L-同型半胱氨酸硫内酯（L-HCT，10微摩尔）和腺苷脱氨酶抑制剂erythro-9-(2-羟基-3-壬基)-腺嘌呤（EHNA，10微摩尔），可增加SAM介导的甲基化抑制剂S-腺苷同型半胱氨酸（SAH）的细胞内水平。每小时测定一次每种精子悬液的运动指数，持续4小时。在腺苷、L-HCT和EHNA的混合物存在下，运动指数降低了57%。在类似条件下，磷脂甲基化降低了48%。在SAH水解酶的选择性抑制剂3-脱氮腺苷（Deaza，80微摩尔）存在下也进行了类似的实验。在腺苷和L-HCT存在下，Deaza使运动指数降低了60%，磷脂甲基化降低了86%。SAH在抑制精子匀浆中磷脂甲基化和蛋白质羧甲基化方面的效力顺序如下：PMT I＞PCM＞PMT II。这些观察结果表明，PMT系统和/或PCM-MAP系统在人类精子运动的调节中起重要作用。
