Advances in the molecular characterization of tryptophan hydroxylase

被引:78
作者
Mockus, SM
Vrana, KE [1 ]
机构
[1] Wake Forest Univ, Sch Med, Dept Physiol & Pharmacol, Ctr Neurobiol Invest Drug Abuse, Winston Salem, NC 27157 USA
[2] Wake Forest Univ, Sch Med, Dept Physiol & Pharmacol, Program Neurosci, Winston Salem, NC 27157 USA
关键词
tryptophan hydroxylase; regulation; serotonin; phosphorylation; nitric oxide; biogenic amines; L-DOPA;
D O I
10.1007/BF02761772
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The neurotransmitter serotonin has been implicated in numerous physiological functions and pathophysiological disorders. The hydroxylation of the aromatic amino acid tryptophan is rate-limiting in the synthesis of serotonin. Tryptophan hydroxylase (TPH), as the rate-limiting enzyme, determines the concentrations of serotonin in vivo. Relative serotonin concentrations are clearly important in neural transmission, but serotonin has also been reported to function as a local antioxidant. Identification of the mechanisms regulating TPH activity has been hindered by its low levels in tissues and the instability of the enzyme. Several TPH expression systems have been developed to circumvent these problems. In addition, eukaryotic expressions systems are currently being developed and represent a new avenue of research for identifying TPH regulatory mechanisms. Recombinant DNA technology has enabled the synthesis of TPH deletions, chimeras, and point mutations that have served as tools for identifying structural and functional domains within TPH. Notably, the experiments have proven long-held hypotheses that TPH is organized into N-terminal regulatory and C-terminal catalytic domains, that serine-58 is a site for PKA-mediated phosphorylation, and that a C-terminal leucine zipper is involved in formation of the tetrameric holoenzyme. Several new findings have also emerged regarding regulation of TPH activity by posttranslational phosphorylation, kinetic inhibition, and covalent modification. Inhibition of TPH by L-DOPA may have implications for depression in Parkinson's disease (PD) patients. In addition, TPH inactivation by nitric oxide may be involved in amphetamine-induced toxicity. These regulatory concepts, in conjunction with new systems for studying TPH activity, are the focus of this article.
引用
收藏
页码:163 / 179
页数:17
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