pPrenylated protein methyltransferase, an enzyme involved in the post-translational modification of many signalling proteins, has been characterized in a parasitic flagellated protozoan, iLeishmania donoiv/iani./i The activity of this enzyme was monitored by the methylation of an artificial substrate, an S-prenylated cysteine analogue, with iS/i-adenosyl-L-[imethyl/i-sup3/supH]methionine as methyl donor. More than 85% of the methyltransferase activity was associated with membranes. The enzyme methylates iN/i-acetyl-iS/i-itrans/i,itrans-/ifarnesyl-L-cysteine and iN/i-acetyl-iS/i-all-itrans/i-geranylgeranyl-L-cysteine, but iN/i-acetyl-iS/i-itrans/i,itrans/i-geranyl-L-cysteine only very weakly. In contrast with the enzyme from mammals, the leishmanial enzyme had a greater affinity for the farnesylated substrate than for the geranylgeranylated one. Activity iin iv/iitro/i was not modulated by cAMP, protein kinase C activator or guanosine 5′-[γ-thio]triphosphate. An analysis of the endogenous substrates showed that the carboxymethylated proteins were also isoprenylated. The main carboxymethylated proteins have molecular masses of 95, 68, 55, 46, 34-23, 18 and less than 14 kDa. Treatment of cells with iN/i-acetyl-iS/i-itrans/i,itrans-/ifarnesyl-L-cysteine decreased the carboxymethylation level, whereas treatment with guanosine 5′-[γ-thio]triphosphate increased the carboxymethylation of various proteins, particularly those of molecular masses 30-20 kDa./p
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机译：>异戊酸化的蛋白质甲基转移酶是一种参与许多信号蛋白翻译后修饰的酶，其特征是寄生有鞭毛的原生动物 Leishmania dono v ani。该酶的活性通过人工底物S-异戊二酸半胱氨酸类似物与 S -腺苷基-L-[甲基- 3 <甲硫氨酸为甲基供体。超过85％的甲基转移酶活性与膜有关。酶甲基化 N -乙酰基- S -反式，反式-法呢基-L-半胱氨酸和 N -乙酰基- S -所有-反式-香叶基香叶基-L-半胱氨酸，但 N -乙酰基- S - trans ， trans -香叶基-L-半胱氨酸非常弱。与来自哺乳动物的酶相反，利什曼酶对法呢基化底物的亲和力大于对香叶基香叶基化的底物。 cAMP，蛋白激酶C激活剂或鸟苷5'-[γ-硫代]三磷酸酯未调节 v itro 中的活性。内源底物的分析表明，羧甲基化的蛋白质也被异戊二烯基化。主要的羧甲基化蛋白的分子量为95、68、55、46、34-23、18和小于14 kDa。用 N -乙酰基- S -反式，反式-法呢基-L-半胱氨酸处理细胞会降低羧甲基化水平，而鸟苷5'-[γ-硫代]三磷酸处理增加了各种蛋白质的羧甲基化，特别是分子量为30-20 kDa的蛋白质。
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