Carmody J M, Herriott R M
J Bacteriol. 1970 Feb;101(2):525-30. doi: 10.1128/jb.101.2.525-530.1970.
The influence of ribo- and deoxyribonucleosides and ribo- and deoxyribonucleotides on the uptake of radiolabeled thymidine and thymine by Haemophilus influenzae during growth was investigated. A nucleoside-degrading enzyme similar to that reported in Escherichia coli was found to break down thymidine unless other nucleosides were present to divert its action. The presence of other nucleosides permitted a nearly quantitative uptake of even low levels of thymidine. This quantitative uptake of thymidine in the presence of an excess of other nucleosides suggests that the uptake mechanism for thymidine is specific in this organism. Under optimal conditions, as much as 50% of the deoxyribonucleic acid (DNA) thymine was derived from exogenous thymidine. Thymine was not taken up by H. influenzae but, in the presence of purine deoxynucleosides, labeled thymine entered the cells, presumably as thymidine. Ribonucleosides or ribonucleotides inhibited thymine conversion to thymidine, but, as noted above, they were degraded by a cellular enzyme. Thus, unless the ribonucleoside level was excessively high, a cell level of growth was reached at which the inhibiting ribonucleoside was broken down and labeled thymine appeared in the cells at an increasing rate. Twenty-five per cent of the DNA thymine of this organism was labeled with exogenous thymine. The information noted above serves as the basis for isotopically labeling the DNA.
研究了核糖核苷、脱氧核糖核苷、核糖核苷酸和脱氧核糖核苷酸对流感嗜血杆菌生长过程中放射性标记胸苷和胸腺嘧啶摄取的影响。发现一种类似于大肠杆菌中报道的核苷降解酶会分解胸苷，除非有其他核苷存在以转移其作用。其他核苷的存在使得即使低水平的胸苷也能几乎定量摄取。在过量其他核苷存在的情况下胸苷的这种定量摄取表明该生物体中胸苷的摄取机制具有特异性。在最佳条件下，多达50%的脱氧核糖核酸（DNA）胸腺嘧啶来自外源胸苷。流感嗜血杆菌不摄取胸腺嘧啶，但在嘌呤脱氧核苷存在的情况下，标记的胸腺嘧啶进入细胞，推测是以胸苷的形式。核糖核苷或核糖核苷酸会抑制胸腺嘧啶转化为胸苷，但如上所述，它们会被细胞内的一种酶降解。因此，除非核糖核苷水平过高，否则会达到一个细胞生长水平，此时抑制性核糖核苷被分解，标记的胸腺嘧啶以越来越快的速度出现在细胞中。该生物体25%的DNA胸腺嘧啶用外源胸腺嘧啶标记。上述信息为DNA的同位素标记奠定了基础。
