The activity of thymidine kinase in rat liver supernatant decreased with development to a value in the adult that was 1% of that in the 17-day foetus. 2. The foetal enzyme was more stable than the adult to gel filtration on Sephadex G-25 at 0 degrees . 3. The greater stability of the foetal enzyme to incubation at 45 degrees was attributable to the presence of higher concentrations of nucleotides in foetal liver supernatant. 4. The K(m) values for foetal and adult enzymes were approx. 2.5mum- and 2.1mum-thymidine respectively. 5. The foetal enzyme was more sensitive to inhibition by thymidine triphosphate. 6. The decline in enzyme activity during the neonatal period was correlated with a shift in the enzyme properties from the foetal to the adult type, and may reflect the decrease in the proportion of haemopoietic tissue in the liver.
摘要
大鼠肝脏上清液中胸苷激酶的活性随着发育而降低,在成年时的值仅为17日龄胎儿时的1%。2. 在0℃下,胎儿酶在Sephadex G - 25凝胶过滤中比成人酶更稳定。3. 胎儿酶在45℃孵育时具有更高的稳定性,这归因于胎儿肝脏上清液中核苷酸浓度较高。4. 胎儿和成人酶的K(m)值分别约为2.5μM和2.1μM胸苷。5. 胎儿酶对三磷酸胸苷的抑制更敏感。6. 新生儿期酶活性的下降与酶性质从胎儿型向成人型的转变相关,这可能反映了肝脏中造血组织比例的降低。