Aromatic N-hydroxyguanidines as new reduction cosubstrates for dopamine beta-hydroxylase.
Conversion of neurotransmitter dopamine into norepinephrine is catalyzed by dopamine beta-hydroxylase (DbH). The reaction requires the presence of both molecular oxygen and a reducing cosubstrate, the assumed physiological cosubstrate being ascorbic acid. We have investigated the ability of a new family of molecules, N-aryl-N'-hydroxyguanidines, to serve as cosubstrates for DbH. N-(4-Methoxyphenyl)-N'-hydroxyguanidine proved to be an efficient reducing agent for DbH. The complete N-hydroxyguanidine moiety was required for activity, as any modification of this function resulted in non-cosubstrate compounds. Moreover, analysis of the products formed from N-(4-methoxyphenyl)-N'-hydroxyguanidine showed that the main oxidation product was a nitrosoimine. Modification of the aromatic para-substituent evidenced an influence of its electronic properties on the catalytic activity whereas steric factors seemed less important. In addition, changing the methoxy-substituent from the para- to the ortho-position led to an inactive compound. Our results demonstrate that N-aryl-N'-hydroxyguanidines are new efficient reducing cosubstrates for DbH and prove that specific interactions with the reducing cosubstrate do take place at the active site of the enzyme.
Slama
Patrick
P
Chimie, Biologie et Radicaux libres, UMR-CNRS 6517, Faculté des Sciences et Techniques de Saint-Jérome, case 432, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20, France. patrick.slama@iaf.cnrs-gif.fr
Boucher
Jean-Luc
JL
Réglier
Marius
M
D003300:Copper / Q000737:chemistry*; D004299:Dopamine beta-Hydroxylase / Q000737:chemistry*; D004789:Enzyme Activation; D006146:Guanidines / Q000737:chemistry*; D006841:Hydrocarbons, Aromatic; D006898:Hydroxylamines; D007700:Kinetics; D009655:Octopamine / Q000138:chemical synthesis*; D010084:Oxidation-Reduction; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D006146:Guanidines; D006841:Hydrocarbons, Aromatic; D006898:Hydroxylamines; D009655:Octopamine; D003300:Copper; C029604:hydroxyguanidine; D004299:Dopamine beta-Hydroxylase