Roy-Burman S, Visser D W
J Biol Chem. 1975 Dec 25;250(24):9270-5.
The characteristics of adenine, guanine, hypoxanthine, xanthine, and uracil uptake in Escherichia coli B show that each base is transported by a specific system. The data support the concept that the transport of guanine, hypoxanthine, xanthine, and uracil function without direct involvement of the respective purine or pyrimidine phosphoribosyltransferase enzymes. Uracil phosphoribosyltransferase is not demonstrable in E. coli B, and large differences are observed in the inhibitory effects of heterologous purines on the uptake of guanine, hypoxanthine, and xanthine as compared to the corresponding inhibitory effects reported for the soluble purine phosphoribosyltransferase enzymes of E. coli B. Additional evidence is provided by the low Km values determined for the transport of adenine, guanine, hypoxanthine, and xanthine relative to the corresponding Km values for the phosphoribosyltransferase enzymes. Data are presented indicating that adenine may be transported without participation of adenine phosphoribosyltransferase. The stimulatory effect of glucose, the inhibitory effect of KCN, and the high intracellular to extracellular concentration gradients of the bases produced in the presence of glucose provide evidence that the transport processes are energy-dependent. The Km values for transport of the purines and uracil range from 10(-7) M to 5 X 10(-7) M. Characteristics of adenine and uracil uptake are similar in E. coli B, E. coli K-12, and a showdomycin-resistant mutant of E. coli B. Adenosine and deoxyadenosine are transported in E. coli B by independent transport systems. Adenine or hypoxanthine does not share the adenosine or deoxyadenosine transport systems as evidence by the mutual lack of competition of free bases and nucleosides on transport. The transport systems for deoxyadenosine and adenosine are defective in the mutant.
大肠杆菌B中腺嘌呤、鸟嘌呤、次黄嘌呤、黄嘌呤和尿嘧啶摄取的特征表明，每种碱基都是通过特定系统进行转运的。这些数据支持这样一种概念，即鸟嘌呤、次黄嘌呤、黄嘌呤和尿嘧啶的转运在各自的嘌呤或嘧啶磷酸核糖基转移酶未直接参与的情况下发挥作用。在大肠杆菌B中未检测到尿嘧啶磷酸核糖基转移酶，并且与报道的大肠杆菌B可溶性嘌呤磷酸核糖基转移酶的相应抑制作用相比，观察到异源嘌呤对鸟嘌呤、次黄嘌呤和黄嘌呤摄取的抑制作用存在很大差异。相对于磷酸核糖基转移酶的相应Km值，为腺嘌呤、鸟嘌呤、次黄嘌呤和黄嘌呤的转运测定的低Km值提供了额外的证据。所呈现的数据表明，腺嘌呤的转运可能无需腺嘌呤磷酸核糖基转移酶的参与。葡萄糖的刺激作用、KCN的抑制作用以及在葡萄糖存在下产生的碱基的高细胞内与细胞外浓度梯度提供了证据，表明转运过程是能量依赖性的。嘌呤和尿嘧啶转运的Km值范围为10^(-7) M至5×10^(-7) M。大肠杆菌B、大肠杆菌K - 12以及大肠杆菌B的对showdomycin耐药的突变体中腺嘌呤和尿嘧啶摄取的特征相似。腺苷和脱氧腺苷在大肠杆菌B中通过独立的转运系统进行转运。游离碱基和核苷在转运上相互缺乏竞争，这证明腺嘌呤或次黄嘌呤并不共享腺苷或脱氧腺苷的转运系统。脱氧腺苷和腺苷的转运系统在该突变体中存在缺陷。
