Tondeur-Six N, Tencer R, Brachet J
Biochim Biophys Acta. 1975 Jun 2;395(1):41-7. doi: 10.1016/0005-2787(75)90231-2.
Uniformly labeled [3H] uridine is incorporated into DNA by dissociated Pleurodeles blastulae; the label is found in cytosine and to a much lesser extent in thymine. Ribonucleotide reductase activity cannot be detected in full grown oocytes of Xenopus and Pleurodeles, but is present in unfertilized egg. The enzyme is synthesized (or activated) when maturation is induced in Xenopus oocytes by in vitro hormonal treatment. The enzymatic activity increases after fertilization and reaches a peak at the 2--4 cell stage; it decreases at the blastula, gastrula and neurula stages to the low level initially present in unfertilized eggs. The enzyme is no longer detectable in swimming tadpoles. Addition of hydroxyurea (1 mg/ml) to fertilized eggs leads to complete loss of ribonucleotide reductase activity: cycloheximide (20 mug/ml) inhibits the rise in activity characteristic of early cleavage, while actinomycin D (20 mug/ml) has no effect. The significance of these results in discussed.
解离的有尾目蝾螈囊胚可将均匀标记的[3H]尿苷掺入DNA中；该标记存在于胞嘧啶中，在胸腺嘧啶中的含量则少得多。非洲爪蟾和有尾目蝾螈的成熟卵母细胞中检测不到核糖核苷酸还原酶活性，但未受精卵中存在该酶。当通过体外激素处理诱导非洲爪蟾卵母细胞成熟时，该酶会被合成（或激活）。受精后酶活性增加，并在2-4细胞期达到峰值；在囊胚、原肠胚和神经胚期活性降低至未受精卵最初的低水平。在游动的蝌蚪中不再能检测到该酶。向受精卵中添加羟基脲（1毫克/毫升）会导致核糖核苷酸还原酶活性完全丧失：放线菌酮（20微克/毫升）抑制早期卵裂特征性的活性升高，而放线菌素D（20微克/毫升）则没有影响。讨论了这些结果的意义。
