Yarlett N, Quamina A, Bacchi C J
Haskins Laboratories, Department of Biology, Pace University, New York, NY 10038.
J Gen Microbiol. 1991 Mar;137(3):717-24. doi: 10.1099/00221287-137-3-717.
Protein methylases I, II and III were detected in extracts of Trypanosoma brucei brucei, and characterized according to the specific amino substituent methylated. Only protein methylase II activity was elevated by difluoromethylornithine treatment of T. b. brucei, and hence this enzyme was characterized further. Protein methylase II transferred methyl groups from S-adenosyl-L-methionine (S-AdoMet) to the carboxyl residues of several protein substrates, exhibiting highest activity with histone VIII-S (arginine-rich subgroup f3). The crude enzyme had an apparent Km for histone VIII-S of 28 mg ml-1 (11.4 mM-aspartyl and 18.4 mM-glutamyl residues methylated), and an apparent Km for S-AdoMet of 8.4 microM. T. b. brucei protein methylase II was sensitive to inhibition by S-adenosyl-L-homocysteine and its analogue sinefungin with apparent Ki values of 12.9 and 1.6 microM, respectively. Using a partially purified preparation, analysis of kinetic data in the presence and absence of sinefungin indicated that this analogue acts as a competitive inhibitor of the S-AdoMet binding site, and as a non-competitive inhibitor of the (protein) histone VIII-S binding site. The possible role of the enzyme in morphological control and its potential as a chemotherapeutic target are discussed.
在布氏布氏锥虫提取物中检测到了蛋白质甲基化酶I、II和III，并根据甲基化的特定氨基取代基对其进行了表征。只有蛋白质甲基化酶II的活性在经二氟甲基鸟氨酸处理的布氏布氏锥虫中有所升高，因此对该酶进行了进一步表征。蛋白质甲基化酶II将甲基从S-腺苷-L-甲硫氨酸（S-AdoMet）转移到几种蛋白质底物的羧基残基上，对富含精氨酸的f3亚组组蛋白VIII-S表现出最高活性。粗酶对组蛋白VIII-S的表观Km为28 mg/ml（11.4 mM-天冬氨酰和18.4 mM-谷氨酰残基甲基化），对S-AdoMet的表观Km为8.4 μM。布氏布氏锥虫蛋白质甲基化酶II对S-腺苷-L-高半胱氨酸及其类似物杀稻瘟菌素敏感，表观Ki值分别为12.9和1.6 μM。使用部分纯化的制剂，在有和没有杀稻瘟菌素的情况下对动力学数据进行分析表明，该类似物作为S-AdoMet结合位点的竞争性抑制剂，以及（蛋白质）组蛋白VIII-S结合位点的非竞争性抑制剂。讨论了该酶在形态控制中的可能作用及其作为化疗靶点的潜力。
