Tsuda M, Katunuma N, Weber G
J Biochem. 1979 May;85(5):1347-54.
Glutamine 5-phosphoribosyl-1-pyrophosphate (PRPP) amidotransferase (amidophosphoribosyltransferase), [EC 2.4.2.14] was purified 1,600-fold from rat liver. The preparation gave two protein bands on acrylamide gel electrophoresis, of which only the main band showed enzyme activity. The molecular weight of the enzyme was estimated to be 215,000, 200,000, and 195,000 by Sephadex G-150 gel filtration, polyacrylamide gel electrophoresis, and sucrose density grandient ultracentrifugation, respectively. The apparent Km values for glutamine and PRPP were 1.24 mM and 0.57 mM, respectively. The concentration-activity curve for PRPP changed from a hyperbolic to a sigmoidal form on addition of AMP or GMP, and this inhibition by AMP was prevented by increasing the PRPP concentration. In the presence of high concentrations of inorganic phosphate, the catalytic activity was decreased and the sensitivity to AMP inhibition was slightly increased. The molecular size of liver amidotransferase was not changed by the addition of PRPP, AMP, or 2-mercaptoethanol. The purified rat liver enzyme has a broad pH-range of activity between 6.5 and 8.5.
谷氨酰胺5-磷酸核糖基-1-焦磷酸（PRPP）酰胺转移酶（酰胺磷酸核糖基转移酶），[EC 2.4.2.14] 从大鼠肝脏中纯化了1600倍。该制剂在丙烯酰胺凝胶电泳上呈现两条蛋白带，其中只有主带显示酶活性。通过Sephadex G-150凝胶过滤、聚丙烯酰胺凝胶电泳和蔗糖密度梯度超速离心法分别估计该酶的分子量为215,000、200,000和195,000。谷氨酰胺和PRPP的表观Km值分别为1.24 mM和0.57 mM。添加AMP或GMP后，PRPP的浓度-活性曲线从双曲线形式变为S形，并且通过增加PRPP浓度可防止AMP的这种抑制作用。在高浓度无机磷酸盐存在下，催化活性降低，对AMP抑制的敏感性略有增加。添加PRPP、AMP或2-巯基乙醇后，肝脏酰胺转移酶的分子大小不变。纯化的大鼠肝脏酶在6.5至8.5之间具有较宽的活性pH范围。
