Vilpo J A, Vilpo L M
Department of Clinical Chemistry, Tampere University Hospital, Finland.
Mutat Res. 1993 Apr;286(2):217-20. doi: 10.1016/0027-5107(93)90186-j.
Nucleoside monophosphate kinase (EC 2.7.4.4) catalyzes the phosphorylation of various nucleoside monophosphates to their corresponding diphosphates. We investigated whether 5-methyl-2'-deoxycytidine 5'-monophosphate (5MedCMP) could serve as a substrate for the enzyme isolated from bovine liver. Although the substrate activity of UMP, CMP and dCMP was readily demonstrable, no activity was recorded with 5MedCMP as the candidate substrate. Moreover, 5MedCMP did not affect the active site of the enzyme, since no inhibition in the phosphorylation of UMP was recorded in the presence of 5MedCMP. This metabolic step appears to be the key phase where the incorporation of exogenous 5-methylcytosine (5MeCyt) into DNA is prevented. Hence, very little or no salvage of DNA 5MeCyt can be expected.
核苷单磷酸激酶（EC 2.7.4.4）催化各种核苷单磷酸磷酸化为其相应的二磷酸核苷。我们研究了5-甲基-2'-脱氧胞苷5'-单磷酸（5MedCMP）是否可以作为从牛肝脏中分离出的该酶的底物。尽管尿苷单磷酸（UMP）、胞苷单磷酸（CMP）和脱氧胞苷单磷酸（dCMP）的底物活性很容易得到证明，但以5MedCMP作为候选底物时未记录到活性。此外，5MedCMP不会影响该酶的活性位点，因为在存在5MedCMP的情况下，未记录到UMP磷酸化受到抑制。这一代谢步骤似乎是阻止外源5-甲基胞嘧啶（5MeCyt）掺入DNA的关键阶段。因此，可以预期DNA 5MeCyt的补救合成很少或几乎没有。
