Dopamine-p-monooxygenase

DBM dopamine P-monooxygenase GDPH glycerol phosphate dehydrogenase... 

Such a species cannot be ruled out in reactions of iron-EDTA complexes with hydroperoxides recently described by Bruice and coworkers (27). On the other hand, a hydroperoxide complex that reacts with the substrate such that bond formation fiom O to substrate is concerted with 0-0 bond breaking, as proposed by Klinman for dopamine P-monooxygenase (18), could provide compensation for the cost of 0-0 bond cleavage in the transition state. In fact, it is interesting to speculate that for each of these enzymes, the mechanism by which the substrate is oxidized may be dependent on the reactivity of the substrate. One could envision certain substrates that would react with the metal-bound hydroperoxide ligand prior to or concerted with 0-0 bond cleavage. This possibility is difficult to assess because of our lack of information concerning the reactivity of HQ2" when complexed to different metal ions. 

The type-3 copper of hemocyanins and tyrosinases is usually EPR silent with the exception e.g. of Helixpomatia methemocyanin. Dopamine P-monooxygenase has been described to contain only type-2 copper according to EPR data but there seems kinetic evidence for a transient binuclear site... 

It has been suggested that the activation of dopamine 3-monooxygenase by ascorbate was due to the formation of OJ by reduction of O, as the enzyme was activated by O J and inhibited by BESOD This inhibition of the enzyme could not be confirmed Dopamine P-monooxygenase could, moreover, be activated... 

The autoxidation of ascorbate, a cosubstrate of dopamine P-monooxygenase, induces the degradation of most proteins including catalase and dopamine p-monooxygenase, but with the exception of (Cu,Zn)-SOD. Catalase protects dopamine P-monooxy-genase and is therefore generally added in the assay systems . The apparent activation or rather the stabilization of the enzyme (6.5 pg) by small amounts of catalase (3.1 pg) was enhanced by native but not by boiled SOD (100 pg) and also by similar amounts of serumalbumin (100 pg) or of boiled catalase (65 pg)... 

The effect of SOD points to the intervention of Oj in the autoxidation of ascorbate. Proteins in large amounts could react with the strong oxidizing agent formed in this Udenfriend s system , thus protecting the enzyme. The ineffectiveness of boiled SOD could be due to its amino-acid composition (See Sect. 4.1.2). While O did not inactivate dopamine P-monooxygenase the rate pf inactivation in the presence of... 

Dopamine P-monooxygenase 887 Double displacement reactions 595 ping-pong mechanism 595 in ribonuclease 647 Double helices 201,213-218... 

In vivo tolerance to copper is quite high, however, deficiency and excess are serious problems. Infants are particularly vulnerable as they take time to assimilate the correct levels and it is known that trace copper from cooking utensils or water pipes can cause childhood cirrhosis. Copper deficiency leads to arterial weakness and heart enlargement. This is probably caused by a decrease in catecholamine neurotransmitters derived from the biosynthesis of adrenaline which requires the copper-containing enzymes phenylalanine hydroxylase, dopamine P-monooxygenase and tyrosinase. 

FIGURE 9.86 Ascorbate is requited for the activity of dopamine hydroxylase, also called dopamine-p-monooxygenase. The mechanism of the reaction is quite similar to that of amidating en2)nne, an ascorbate-requiring enzyme that catalyzes the hydroxylation of pol)q)eptides, during the course of a two-step sequence. 

FIGURE 9.87 Ascorbate is used for the synthesis of amidated hormones. Two molecules of ascorbate are used for the production of one molecule of amidated hormone, where each ascorbate is converted to semidehydroascorbic acid. Glyoxylate is a b)rproduct of the reaction. The reaction occurs in two steps, which are catalyzed by a bifunctional enzyme, as revealed in the text. The chemistry of the first reaction, which results in the hydroxyla-tion of the substrate, is quite similar to that catalyzed by dopamine-p-monooxygenase. 

We have been interested in the noncoupled copper-monooxygenases comprising Peptidylglycine a-Monooxygenase (PHM), Dopamine p-Monooxygenase (DpM), and Tyramine p-Monooxygenase (TpM) that catalyze the hydroxylation of C-H... 

Dopamine P-monooxygenase, EC 1.14.17.1, which hydroxylates dopamine to noradrenalin (ascorbate donates the hydrogens for reduction of the second oxygen atom). 

Dopamine-p-monooxygenases (DpM) play important roles in the catecholamine biosynthesis and catalyze the conversion of dopamine to neurotransmitter and hormone norepinepherine [183]. In addition to the physiological reactions, DpM also catalyzes a wide variety of monooxygenation reactions, ketonization of phenylethanolamines [184, 185] and p-halo phenylethanolamines [186-188], epoxidation of alkenes [189], N-dealkylation of benzylic N-substituted analogs [189, 190], and allylic hydroxylation [191]. The reaction catalyzed by DpM requires dioxygen and ascorbate, the most... 

Tian GC, Berry JA, Klinman JP. 1994. 0-18 kinetic isotope effects in the dopamine P-monooxygenase reaction evidence for a new chemical mechanism in nonheme metal-lomonooxygenases. Biochemistry 33 226—234. 

Evans JP, Ahn K, Klinman JP. 2003. Evidence that dioxygen and substrate activation are tightly coupled in dopamine P-monooxygenase implications for the reactive oxygen species. JBiol Chem 278 49691—49698. 

Wimalasena K, Dharmasena S. Substrate specificity of ascorbate oxidase unexpected similarity to the reduction site of dopamine p-monooxygenase. Biochem Biophys Res Commun 1994 203 1471-1476. 

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