title: Inhibition of choline oxidase by quinoid dyes.
abstract: Choline oxidase catalyzes the oxidation of choline to glycine-betaine, with betaine-aldehyde as intermediate and molecular oxygen as primary electron acceptor. This study reports on the inhibitory effects of triarylmethanes (cationic malachite green; neutral leukomalachite green), phenoxazines (cationic, meldola blue and nile blue; neutral nile red) and a structurally-related phenothiazine (methylene blue) on choline oxidase, assayed at 25 degrees C in 50 mM MOPS buffer, pH 7, using choline as substrate. Methylene B acted as a competitive inhibitor with K(i) = 74 +/- 7.2 microM, pointing to the choline-binding site of the enzyme as a target site. Nile B caused noncompetitive inhibition of enzyme activity with K(i) = 20 +/- 4.5 microM. In contrast to methylene B and nile B, malachite G and meldola B caused complex, nonlinear inhibition of choline oxidase, with estimated K(i) values in the micromolar range. The difference in kinetic pattern was ascribed to the differential ability of the dyes to interact (and interfere) with the flavin cofactor, generating different perturbations in the steady-state balance of the catalytic process.
authors.affiliation: Department of Biochemistry, School of Pharmacy, Hacettepe University, 06100 Ankara, Turkey. tacal@hacettepe.edu.tr
authors.forename: Ozden
authors.initials: O
authors.lastname: Tacal
authors.forename: Inci
authors.initials: I
authors.lastname: Ozer
mesh_terms: D000429:Alcohol Oxidoreductases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002384:Catalysis; D003067:Coenzymes / Q000378:metabolism; D004396:Coloring Agents / Q000737:chemistry / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D007700:Kinetics; D008751:Methylene Blue / Q000494:pharmacology; D010078:Oxazines / Q000494:pharmacology; D012394:Rosaniline Dyes / Q000494:pharmacology
chemical_list: D003067:Coenzymes; D004396:Coloring Agents; D004791:Enzyme Inhibitors; D010078:Oxazines; D012394:Rosaniline Dyes; C005095:malachite green; C039203:phenoxazine; D000429:Alcohol Oxidoreductases; C019888:choline oxidase; D008751:Methylene Blue