Peptidylglycine a-hydroxylating

PHM peptidylglycine a-hydroxylating monooxygenase RVM rostral ventromedial medulla... 

Figure 14.3 The reaction catalysed by peptidylglycine a-hydroxylating monooxygenase.

Figure 14.4 The dioxygen site in peptidylglycine a-hydroxylating monooxygenase incubated in the presence of IYT. (From Bento et al., 2006. With kind permission of Springer Science and Business Media.)...

Chen, P. and Solomon, E.I. (2004). Oxygen activation by the noncoupled binuclear copper site in peptidylglycine-a-hydroxylating monoxygenase. Reaction mechanism and role of the noncoupled nature of the active site. J. Am. Chem. Soc. 126, 4991-5000... 

Peptidyl-a-hydroxylating monoxygenase, 67-68 Peptidylglycine a-hydroxylating monoxygenase, A9t... 

Somewhat related to the chemistry observed with the peptidylglycine-a-hydroxylating monoxygenase (PHM), the aerobic oxidation of cyclohexane has been studied by several groups. Murahashi et al. have reported that with CuCl2 and acetaldehyde and in the presence of 18-crown-6, cyclohexanone was obtained as the major product (cyclohexanol was formed as the major by-product) under relativelymild conditions (70 °C) [109,110]. Turnover numbers of up to 1600 were achieved with 61% yield of cyclohexanone at 1 atm of O2, but the precise mechanism has not been elucidated (Eq. 7). 

Tyrosinase is both an oxidase and a hydroxylase. Some other copper enzymes have only a hydroxylase function. One of the best understood of these is the peptidylglycine a-hydroxylating monoxygenase, which catalyzes the first step of the reaction of Eq. 10-11. The enzyme is a colorless two-copper protein but the copper atoms are 1.1 nm apart and do not form a binuclear center.570 Ascorbate is an essential cosubstrate, with two molecules being oxidized to the semidehydro-ascorbate radical as both coppers are reduced to Cu(I). A ternary complex of reduced enzyme, peptide, and 02 is formed and reacts to give the hydroxylated product.570 A related two-copper enzyme is dopamine (J-monooxygenase, which utilizes 02 and ascorbate to hydroxylate dopamine to noradrenaline (Chapter 25).571/572 These and other types of hydroxylases are compared in Chapter 18. 

Klinman JP. The copper-enzyme family of dopamine 3-mono-oxygenase and peptidylglycine a-hydroxylating monooxygenase resolving the chemical pathway for substrate hydroxylation. J. Biol. Chem. 2006 281 3013-3016. 

Finally, many enzymes are kinetically complex, and have multiple steps that partially limit both k at and k t/KM. One approach is to use single-turnover studies to obtain the rate of the chemical step and the kinetic isotope effects by this noncompetitive technique. Several examples of single-turnover studies of enzymes that exhibit the characteristic of turmeling are in the literature [11, 12]. Alternatively, tools that allow microscopic rate constants to be calculated from observed rate constants can be applied. This approach has been documented for peptidylglycine-a-hydroxylating monooxygenase [13], and more recently, for dihydrofolate reductase [14]. 

Peptidylamidoglycolate lyase completes the peptide ami-dation process initiated by peptidylglycine a-hydroxylating monooxygenase vide supra. Section 2.1.3). This zinc-dependent function converts the hydroxyglycine containing peptide to the amidated form and releases glyoxalate (equation 8) ... 

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