Galactose-1-phosphate uridylyltransferase: uridylyl-enzyme中间的隔离和属性。
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黄LJ,张文雄KF,李SL,弗雷PA
Galactose-1-phosphate uridylyltransferase: uridylyl-enzyme中间的隔离和属性。
生物化学,1977年3月8日,16 (5):1010 - 6。
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321007年(在PubMed]
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Galactose-1-P uridylyltransferase催化UDP-galactose互变现象和Galactose-1-P UDP-galactose和glucose-1-P双位移路径涉及uridylyl-enzyme中间。的放射性纳入蛋白质uracil-labeled UDP-glucose减少UDP-galactose的存在,这与UDP-glucose完成uridylylating酶。glucose-1-P释放的量对反应的酶UDP-glucose表明二聚酶包含不止一个每个分子活性位点,平均1.7最活跃的准备。这表明,每个单元都有一个uridylylation站点和类似或相同的子单元。ureidylyl-enzyme稳定温和碱性条件,0.10 M氢氧化钠在60摄氏度1 h,但酸非常敏感,主要是水解后12 h pH值3.5和4度C的主要放射性产品水解产生的[uracil-2-14C] uridylyl-ens uridylyl-enzyme后者条件下的[l]人民运动联盟。的水解性质uridylyl-enzyme表明uridylyl一半连着蛋白质通过phosphoramidate联系。互补的研究小组选择性试剂的影响酶的活动表明,活性部位的亲核试剂uridylyl集团是保税可能是一个组氨酸残基。焦碳酸二乙酯酶迅速灭活的pH值6 0摄氏度,回复:重新激活。UDP-glucose在0.5毫米充分保护酶对焦碳酸二乙酯在70毫米galactose-1-P只有轻微的保护作用。Uridylyl-enzyme焦碳酸二乙酯的灭活率不超过2%的免费酶。 The enzyme is not inactivated by NaBH4 or by NaBH4 in the presence of UDP-glucose. It is not inhibited by 1 mM pyridoxal phosphate or by 0.5 mM 5-nitrosalicylaldehyde at pH 8.6 and it is not inactivated by NaBH4 in the presence of pyridoxal phosphate. The enzyme is inactivated by 5 to 50 muM p-hydroxymercuribenzoate at pH 8.5, but substrates exert no detectable protective effect against this reagent. It is concluded that the enzyme contains at least one essential sulfhydryl group which is not located in the active site in such a way as to be shielded by substrates.