Peptidylglycine--Hydroxylating Monooxygenase Generates Two Hydroxylated Products from Its Mechanism-Based Suicide Substrate, 4-Pheny

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• 作者：William J. Driscoll ; Simone K&ouml ; nig ; Henry M. Fales ; Lewis K. Pannell ; Betty A. Eipper ; and Gregory P. Mueller
• 刊名：Biochemistry
• 出版年：2000
• 出版时间：July 11, 2000
• 年：2000
• 卷：39
• 期：27
• 页码：8007 - 8016
• 全文大小：118K
• 年卷期：v.39,no.27(July 11, 2000)
• ISSN：1520-4995

文摘

The bifunctional enzyme peptidylglycine-mages/gifchars/alpha.gif" BORDER=0>-amidating monooxygenase mediates the conversionof C-terminal glycine-extended peptides to their active mages/gifchars/alpha.gif" BORDER=0>-amidated products. Peptidylglycine-mages/gifchars/alpha.gif" BORDER=0>-hydroxylating monooxygenase (PHM, EC 1.14.17.3) catalyzes the first reaction in this two-step process.The olefinic compound 4-phenyl-3-butenoic acid (PBA) is the most potent irreversible, mechanism-basedPHM inactivator known. While the details of the inhibitory action of PBA on PHM remain undefined,covalent modification of the protein has been proposed as the underlying mechanism. We report herethat, in the process of inactivating PHM, PBA itself serves as a substrate without covalently labeling theenzyme. Approximately 100 molecules of PBA are metabolized per molecule of PHM inactivated, undersaturating conditions. The metabolism of PBA by PHM generates two hydroxylated products, 2-hydroxy-4-phenyl-3-butenoic acid and its allylic isomer, 4-hydroxy-4-phenyl-2-butenoic acid. While one enantiomerfor each product is significantly favored in the reaction, both are produced. From these observations, weconclude that hydroxylated PBA products are formed by a delocalized free radical mechanism and thatthe lack of absolute stereospecificity indicates significant freedom of movement within the catalytic site.The ability of PHM to metabolize PBA suggests that the physiological functions of PHM may includethe hydroxylation of substrates other than those containing terminal glycines.