Majamaa K, Kuutti-Savolainen E R, Tuderman L, Kivirikko K I
Biochem J. 1979 Feb 15;178(2):313-22. doi: 10.1042/bj1780313.
The turnover of prolyl hydroxylase and an immunoreactive protein that corresponds in size to the smaller subunit of the enzyme was studied in vivo after injection of [(3)H]leucine into 11-day chick embryos. The specific radioactivity and total radioactivity of the monomer-size protein were much higher than those of the enzyme tetramers in the cartilaginous bone at 3h and 12h after the radioisotope injection, indicating that the monomer-size protein represents precursors rather than degradation products of the enzyme tetramers. Between 24 and 144h after the injection the specific radioactivity and total radioactivity of the two forms of the enzyme protein showed essentially identical decay rates, the observed specific radioactivity of the monomer-size protein being about 120-130% and total radioactivity about 80% of that of the enzyme tetramers. The true half-life, when corrected for dilution caused by tissue growth and re-utilization of the [(3)H]leucine, was 37.9h for the monomer-size protein and 39.0h for the tetramers. The results obtained in the lung were less reliable owing to high blank radioactivity values in the immunoprecipitation, but even so some definite differences were found between this tissue and the cartilaginous bone. The specific radioactivity of both forms of the enzyme protein at 24h was only about 20-25% of that in the cartilaginous bone. The total radioactivity of the monomer-size protein in the lung remained about 5 times that of the enzyme tetramers, whereas it was only about 0.8 times that of the tetramers in the cartilaginous bone. As in the cartilaginous bone, the decay rates of both forms of the enzyme protein were essentially identical in the lung, with a true half-life of about 46h. The results suggest that the rate of prolyl hydroxylase synthesis is slower in the lung than in the cartilaginous bone, whereas the degradation rates are fairly similar in these two tissues. The data further suggest that, in the lung at least, a large part of the monomer-size protein became degraded without being converted into enzyme tetramers.
向11日龄鸡胚注射[(3)H]亮氨酸后，在体内研究了脯氨酰羟化酶和一种大小与该酶较小亚基相对应的免疫反应性蛋白的更新情况。放射性同位素注射后3小时和12小时，软骨骨中单体大小蛋白的比放射性和总放射性远高于酶四聚体，这表明单体大小蛋白代表酶四聚体的前体而非降解产物。注射后24至144小时之间，两种形式的酶蛋白的比放射性和总放射性显示出基本相同的衰减率，观察到的单体大小蛋白的比放射性约为酶四聚体的120 - 130%，总放射性约为80%。经组织生长引起的稀释和[(3)H]亮氨酸的再利用校正后，单体大小蛋白的真实半衰期为37.9小时，四聚体为39.0小时。由于免疫沉淀中的高本底放射性值，在肺中获得的结果不太可靠，但即便如此，在该组织和软骨骨之间仍发现了一些明显差异。两种形式的酶蛋白在24小时时的比放射性仅约为软骨骨中的20 - 25%。肺中单体大小蛋白的总放射性约为酶四聚体的5倍，而在软骨骨中仅约为四聚体的0.8倍。与软骨骨一样，肺中两种形式的酶蛋白的衰减率基本相同，真实半衰期约为46小时。结果表明，脯氨酰羟化酶在肺中的合成速率比在软骨骨中慢，而这两个组织中的降解速率相当相似。数据进一步表明，至少在肺中，很大一部分单体大小蛋白在未转化为酶四聚体的情况下就被降解了。
