Abate C, Joh T H
Laboratory of Molecular Neurobiology, W.M. Burke Medical Research Institute, Cornell University Medical College, White Plains, NY 10605.
J Mol Neurosci. 1991;2(4):203-15.
Trypsin proteolysis of tyrosine hydroxylase (TH) produces a 34-kDa fragment that is catalytically active but does not contain the regulatory phosphorylation sites. In this report, activation of TH by proteolysis was characterized further. Proteolysis results in a decrease in Kms for both substrate and cofactor. The increase in affinity for cofactor was identical to that produced by phosphorylation with cAMP-dependent protein kinase. Additionally, proteolysis of an N-terminal region containing the regulatory phosphorylation sites was sufficient to produce a decrease in Km for cofactor. Activation of substrate binding required more extensive proteolysis but also corresponded to N-terminal digestion. Moreover, this activation was coincident with a broadened substrate specificity. In combination, these data indicate that the N-terminus of tyrosine hydroxylase regulates cofactor binding and directs substrate specificity.
酪氨酸羟化酶（TH）经胰蛋白酶蛋白水解产生一个34 kDa的片段，该片段具有催化活性，但不包含调节性磷酸化位点。在本报告中，对蛋白水解激活TH的过程进行了进一步表征。蛋白水解导致底物和辅因子的米氏常数（Km）降低。对辅因子亲和力的增加与依赖环磷酸腺苷（cAMP）的蛋白激酶磷酸化所产生的增加相同。此外，对包含调节性磷酸化位点的N端区域进行蛋白水解足以使辅因子的Km降低。底物结合的激活需要更广泛的蛋白水解，但同样对应于N端消化。而且，这种激活与底物特异性的拓宽相吻合。综合来看，这些数据表明酪氨酸羟化酶的N端调节辅因子结合并指导底物特异性。
