Matsuda Y, Shiraki H, Nakagawa H
Cancer Res. 1982 Jan;42(1):112-6.
The properties of adenylosuccinate synthetase [inosine monophosphate:L-aspartate ligase (guanosine 5'-diphosphate-forming) EC 6.3.4.4]) of rat Yoshida sarcoma ascites tumor cells changed during purification. The isoelectric points (pI) of the crude and purified enzymes were 5.0 and 5.9, respectively. The Km values of the crude enzyme for inosine monophosphate, aspartate, and guanosine 5'-triphosphate were calculated to be 99 +/- 1 (S.E.), 870 +/- 40, and 27 +/- 2 microM, respectively, while those of the purified enzyme were 410 +/- 10, 980 +/- 50, and 69 +/- 5 microM, respectively. These data indicate that the crude enzyme should be more effective for activity than the purified one. It was found that the change in pI occurred during diethylaminoethyl cellulose column chromatography and that, during this step a compound, named pI-converting factor (ICF), was separated from the enzyme molecule. On addition of ICF, the pI of the purified enzyme changed from 5.9 to 5.0, indicating that the pI conversion was dependent on ICF and was reversible. ICF was nondialyzable, heat stable, and partly precipitated with 1 N perchloric acid but was not affected by 1 N KOH. It was partially degraded by DNAse I. These results suggest that ICF is a DNA-like compound.
大鼠吉田肉瘤腹水肿瘤细胞中腺苷酸琥珀酸合成酶[肌苷一磷酸:L-天冬氨酸连接酶(生成鸟苷5'-二磷酸)，EC 6.3.4.4]的性质在纯化过程中发生了变化。粗酶和纯化酶的等电点(pI)分别为5.0和5.9。粗酶对肌苷一磷酸、天冬氨酸和鸟苷5'-三磷酸的Km值经计算分别为99±1(标准误)、870±40和27±2μM，而纯化酶的Km值分别为410±10、980±50和69±5μM。这些数据表明粗酶的活性应比纯化酶更高。发现等电点的变化发生在二乙氨基乙基纤维素柱层析过程中，并且在这一步骤中，一种名为等电点转换因子(ICF)的化合物从酶分子中分离出来。加入ICF后，纯化酶的等电点从5.9变为5.0，表明等电点的转换依赖于ICF且是可逆的。ICF不能透析，耐热，部分可被1N高氯酸沉淀，但不受1N氢氧化钾影响。它可被脱氧核糖核酸酶I部分降解。这些结果表明ICF是一种类似DNA的化合物。
