[Stability and catalytic properties of o-diphenol oxidase. 1. Oxidation of o-diphenols].

o-Diphenoloxidase from potato tubers is inactivated in the course of the oxidation reaction of o-diphenols at the level of the enzyme-substrate complex. At 25 degrees C of the reaction mixture the enzyme inactivation rate constants (Kin) in oxidation of 10 mM solutions of the substrates were: for pyrocatechol--0.48 min-1; 3,4-dihydroxyphenylethylamine (DOP-amine)--0.52 min-1; 3,4-dihydroxyphenylalanine (DOPA)--0.17 min-1; noradrenaline--0.12 min-1; 3,4-dihydroxybenzaldehyde (DHBA)--0.032 min-1; 3,4-dihydroxybenzoic acid (DHBAc)--0.01 min-1; gallic acid--0.01 min-1. Kin of the enzyme in oxidation of pyrocatechol does not depend practically on pH, ionic strength and polarity of the medium, but rises with its temperature. For a temperature range from 20 to 40 degrees C the effective activation energy calculated in terms of the Arrhenius equation is equal to 28 kJ/mol and the preexponential value for the given preparation was 38 850 min-1. The enzyme activity is determined by the substituent nature in the substrate molecule: electron-donor groups (--CH2--) accelerate the oxidation as compared to nonsubstituted pyrocatechol and electron-acceptor groups (--COOH, --CHO) make it more difficult. If the o-diphenoloxidase activity in oxidation of a 10 mM solution of pyrocatechol is 100%, then the oxidation rate of DOP-amine taken in the same concentration would be 111, DOPA--61, noradrenaline--24, DOBA--2,7, DHBA--0.7, gallic acid--0.8%.(ABSTRACT TRUNCATED AT 250 WORDS)