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The catalytic reaction of catalase was investigated, by means of a Clark oxygen sensor, in the presence of various concentrations of acetylsalicylic acid. Michaelis-Menten kinetic parameters were determined from Lineweaver-Burk plots, obtained in the absence and in the presence of the inhibitor. The inhibition pattern, suggested by the Lineweave-Burk plots, corresponds to a fully mixed inhibition mechanism. A kinetic method, based on the indicator reaction: [Formula: see text], was developed for the quantitative determination of acetylsalicylic acid. Calibration graphs of the reciprocal value of first-order rate constant versus acetylsalicylic concentration covered the concentration range (2.99-19.98)x10(-4) mol/L, while the detection limit was 4.12x10(-4) mol/L acetylsalicylic acid with a standard deviation of 2.1x10(-5) mol/L.

The inhibitory effect of para-nitrophenol on the catalytic reaction of catalase was investigated. Michaelis-Menten kinetic parameters were determined from Lineweaver-Burk plots obtained in the absence or in the presence of the inhibitor. The inhibitor pattern, revealed by the Lineweaver-Burk plots, suggested a fully mixed inhibition mechanism. Spectrophotometric monitoring of the indicator reaction: H 2 O 2 catalase, para−nitrophenol − −−−−−−−−−−−−−−−− → H 2 O+ 1 2 O 2 in conjunction with initial rate measurements was employed for the kinetic determination of the inhibitor. Calibration plots of initial rate vs. para-nitrophenol concentration were linear in the concentration range 0.9·10 −5 -2.5·10 −5 mol/L and the detection limit was 3·10 −6 mol/L (417 µg/L) para-nitrophenol. Interferences from other phenolic compounds like orto-cresole, metaand orto-nitrophenol were observed.