Wang C C, Cheng H W
J Exp Med. 1984 Oct 1;160(4):987-1000. doi: 10.1084/jem.160.4.987.
Trichomonas vaginalis, a human protozoan parasite known to lack the capability of synthesizing purine and pyrimidine nucleotides de novo, was found also incapable of converting its ribonucleotides to deoxyribonucleotides. The only apparent means of providing deoxyribonucleotides for DNA synthesis relies on salvaging exogenous deoxyribonucleosides by a deoxyribonucleoside phosphotransferase activity in the T. vaginalis 10(5) g pelletable fraction. The activity, constituted by at least two isozymes I and II, can be solubilized by Triton X-100, has a pH optimum of 5.0-6.0, and recognizes only thymidine, deoxyadenosine, deoxyguanosine, and deoxycytidine as the phosphate acceptor. TMP, dAMP, dGMP, dCMP, dUMP, FdUMP, and p-nitrophenylphosphate can serve as phosphate donors. Enzyme I has been purified 10-fold by DEAE-Sepharose chromatography and Sephacryl 200 filtration, and is totally freed of the acid phosphatase of T. vaginalis. It has an estimated molecular weight of 200,000 and Km values of 2-3 mM for the four deoxyribonucleosides, which act on each other as competitive inhibitors. It also possesses phosphatase activity capable of hydrolyzing p-nitrophenylphosphate with a Michaelis constant of 0.74 mM. The rates of hydrolysis are enhanced by thymidine, which suggests that the latter may be the preferred phosphate acceptor, and Enzyme I may be, thus, more a transferase than a phosphatase. This enzyme could be a potential target for antitrichomonial chemotherapy.
阴道毛滴虫是一种已知缺乏从头合成嘌呤和嘧啶核苷酸能力的人体原生动物寄生虫，还被发现无法将其核糖核苷酸转化为脱氧核糖核苷酸。为DNA合成提供脱氧核糖核苷酸的唯一明显途径依赖于通过阴道毛滴虫10(5)g可沉淀部分中的脱氧核糖核苷磷酸转移酶活性来挽救外源性脱氧核糖核苷。该活性由至少两种同工酶I和II组成，可被 Triton X - 100溶解，最适pH为5.0 - 6.0，并且仅识别胸苷、脱氧腺苷、脱氧鸟苷和脱氧胞苷作为磷酸受体。TMP、dAMP、dGMP、dCMP、dUMP、FdUMP和对硝基苯磷酸可作为磷酸供体。酶I已通过DEAE - 琼脂糖色谱和Sephacryl 200过滤纯化了10倍，并且完全去除了阴道毛滴虫的酸性磷酸酶。它的估计分子量为200,000，对四种脱氧核糖核苷的Km值为2 - 3 mM，这四种脱氧核糖核苷彼此作为竞争性抑制剂起作用。它还具有能够水解对硝基苯磷酸的磷酸酶活性，米氏常数为0.74 mM。胸苷可提高水解速率，这表明胸苷可能是首选的磷酸受体，因此酶I可能更像是一种转移酶而非磷酸酶。这种酶可能是抗滴虫化疗的潜在靶点。
