Hirono A, Fujii H, Miwa S
Jpn J Exp Med. 1985 Feb;55(1):37-44.
The biochemical properties of two isozymes of human erythrocyte pyrimidine 5'-nucleotidase (P5N) separated by ion-exchange chromatography were studied. These two isozymes, P5N-I and P5N-IIB, can be distinguished from each other by substrate specificity, pH dependent activity and thermostability. P5N-I is thermolabile and dephosphorylates various pyrimidine 5'-monophosphates optimally around pH 7. UMP and CMP were found to be most effective substrates. P5N-IIB is thermostable and characterized by its high Michaelis constant and maximum velocity for dUMP or dTMP and acidic pH optima. The molecular weight was estimated to be 39,000 for P5N-I and 44,000 for P5N-IIB by gel filtration. These data suggest that these two isozymes are independent proteins and probably encoded by distinct structural gene loci.
研究了通过离子交换色谱法分离的人红细胞嘧啶5'-核苷酸酶（P5N）的两种同工酶的生化特性。这两种同工酶，P5N-I和P5N-IIB，可以通过底物特异性、pH依赖性活性和热稳定性相互区分。P5N-I对热不稳定，在pH 7左右能最佳地使各种嘧啶5'-单磷酸去磷酸化。发现UMP和CMP是最有效的底物。P5N-IIB对热稳定，其特征在于对dUMP或dTMP具有高米氏常数和最大速度，且最适pH为酸性。通过凝胶过滤估计P5N-I的分子量为39,000，P5N-IIB的分子量为44,000。这些数据表明这两种同工酶是独立的蛋白质，可能由不同的结构基因位点编码。
