GUANIDINOACETATE METHYLTRANSFERASE ACTIVITY IN TISSUES AND CULTURED-CELLS
GUANIDINOACETATE METHYLTRANSFERASE ACTIVITY IN TISSUES AND CULTURED-CELLS
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DOI：
10.1016/0003-9861(85)90661-7
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发表时间：
1985-01-01
影响因子：
3.9
通讯作者：
DALY, MM
中科院分区：
文献类型：
--
作者：
DALY, MM
胍乙酸甲基转移酶是催化肌酸生物合成最后一步的酶，以前认为仅限于少数组织，但发现它存在于培养细胞H4 Az C2大鼠肝癌、N4 TG 1小鼠神经母细胞瘤和IMR-90人胎肺成纤维细胞以及大鼠骨骼肌和心肌中。活性在肝癌中最高，但非肝来源的组织和培养细胞的活性为大鼠肝脏的5-20%。透析从培养的细胞或骨骼肌组织制备的100，000 μ l上清液得到的表观Km值对于S-腺苷甲硫氨酸为1.2-3.4 μ M，对于胍基乙酸为0.050-0.096 mM。3种类型的培养细胞的完整单层将培养基中的标记胍基乙酸转化为肌酸，通过色谱行为和与肌酐激酶的反应鉴定。胍基乙酸转化为肌酸的成纤维细胞和神经母细胞瘤细胞在18小时的孵育期间的量表明，合成进行的速度接近Vmax，即使在培养基中含有相对较低的生理浓度的胍基乙酸。成纤维细胞和神经母细胞瘤细胞单层也有能力吸收培养基中提供的肌酸。在用于测量肌酸合成的相同条件下测量由这些细胞的单层摄取的肌酸量。肌酸酐合成量与摄取量的比较表明，合成可以对成纤维细胞和神经母细胞瘤细胞中肌酸酐加磷酸肌酸的细胞内池做出显着贡献。
Guanidinoacetate methyltransferase, the enzyme catalyzing the last step in creatine biosynthesis, was previously considered to be restricted to a few tissues, but it was found to occur in the cultured cells H4Az C2 rat hepatoma, N4TG1 mouse neuroblastoma, and IMR-90 human fetal lung fibroblast, as well as in skeletal and cardiac muscle of the rat. Activity was highest in the hepatoma, but tissues and cultured cells of nonhepatic origin had 5-20% of the activity of rat liver. Dialyzed 100,000 supernatants prepared from cultured cells or skeletal muscle tissue yielded values for apparent Km in the range of 1.2-3.4 .mu.M for S-adenosylmethionine and 0.050-0.096 mM for guanidinoacetate. Intact monolayers of the 3 types of cultured cells converted labeled guanidinoacetate in the culture medium to creatine, which was identified by chromatographic behavior and by reaction with creatinine kinase. The amounts of guanidinoacetate converted to creatine by fibroblasts and neuroblastoma cells during an 18-h period of incubation suggested that synthesis was proceeding at rates approaching Vmax, even in medium containing the relatively low physiological concentrations of guanidinoacetate. Fibroblast and neuroblastoma cell monolayers also have the capacity to take up creatine provided in the culture medium. The amounts of creatine taken up by monolayers of those cells were measured under the same conditions that were used for measurement of creatine synthesis. Comparison of the amounts of creatinine synthesized with the amounts taken up showed that synthesis can make a significant contribution to intracellular pools of creatinine plus phosphocreatine in fibroblasts and neuroblastoma cells.