首页 | 本学科首页   官方微博 | 高级检索  
   检索      


The tyrosine-dependent oxidation of tetrahydropterins by lysolecithin-activated rat liver phenylalanine hydroxylase
Authors:M D Davis  S Kaufman
Institution:Laboratory of Neurochemistry, National Institute of Mental Health, Bethesda, Maryland 20205.
Abstract:In the presence of tyrosine, phenylalanine hydroxylase, which has been activated with lysolecithin, catalyzes the oxidation of tetrahydrobiopterin at a rate 10-20% that of the parallel reaction with phenylalanine. Unlike the reaction with phenylalanine, there is no net concomitant hydroxylation of tyrosine, although the amino acid is still a necessary component. Tyrosine appears to form an abortive complex with the activated enzyme, the pterin cofactor and molecular oxygen. The Km for tetrahydrobiopterin is identical for the reactions with phenylalanine and tyrosine, whereas the Km for tyrosine is approximately 3 1/2 times greater than the Km for phenylalanine. The tyrosine-dependent oxidation of tetrahydrobiopterin proceeds at both pH 6.8 and 8.2 and shows a similar dependence on the pH as that of the physiological reaction. Tetrahydrobiopterin can be replaced by the artificial cofactor, 6-methyltetrahydropterin, in the tyrosine-dependent oxidation at both pH 6.8 and 8.2. As in the parallel reaction with phenylalanine, both the Km for the cofactor and the Km for the aromatic amino acid increase with this substitution.
Keywords:
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号