Woo S L, Gillam S S, Woolf L I
Biochem J. 1974 Jun;139(3):741-9. doi: 10.1042/bj1390741.
Phenylalanine hydroxylase was prepared from human foetal liver and purified 800-fold; it appeared to be essentially pure. The phenylalanine hydroxylase activity of the liver was confined to a single protein of mol.wt. approx. 108000, but omission of a preliminary filtration step resulted in partial conversion into a second enzymically active protein of mol.wt. approx. 250000. Human adult and full-term infant liver also contained a single phenylalanine hydroxylase with molecular weights and kinetic parameters the same as those of the foetal enzyme; foetal, newborn and adult phenylalanine hydroxylase are probably identical. The K(m) values for phenylalanine and cofactor were respectively one-quarter and twice those found for rat liver phenylalanine hydroxylase. As with the rat enzyme, human phenylalanine hydroxylase acted also on p-fluorophenylalanine, which was inhibitory at high concentrations, and p-chlorophenylalanine acted as an inhibitor competing with phenylalanine. Iron-chelating and copper-chelating agents inhibited human phenylalanine hydroxylase. Thiol-binding reagents inhibited the enzyme but, as with the rat enzyme, phenylalanine both stabilized the human enzyme and offered some protection against these inhibitors. It is hoped that isolation of the normal enzyme will further the study of phenylketonuria.
苯丙氨酸羟化酶是从人胎儿肝脏中制备的，并纯化了800倍；它似乎基本上是纯的。肝脏中的苯丙氨酸羟化酶活性局限于一种分子量约为108000的单一蛋白质，但省略初步过滤步骤会导致部分转化为另一种分子量约为250000的具有酶活性的蛋白质。成人和足月婴儿的肝脏中也含有一种单一的苯丙氨酸羟化酶，其分子量和动力学参数与胎儿酶相同；胎儿、新生儿和成人的苯丙氨酸羟化酶可能是相同的。苯丙氨酸和辅因子的K(m)值分别是大鼠肝脏苯丙氨酸羟化酶的四分之一和两倍。与大鼠酶一样，人苯丙氨酸羟化酶也作用于对氟苯丙氨酸，高浓度时对氟苯丙氨酸具有抑制作用，对氯苯丙氨酸作为与苯丙氨酸竞争的抑制剂起作用。铁螯合剂和铜螯合剂抑制人苯丙氨酸羟化酶。巯基结合试剂抑制该酶，但与大鼠酶一样，苯丙氨酸既能稳定人酶，又能提供一定程度的保护使其免受这些抑制剂的影响。希望正常酶的分离将推动苯丙酮尿症的研究。
