[Kinetic analysis of model reactions for enzyme catalysis using kinetic spectra, absorbance-difference diagrams and formal integration].

The significance of isosbestic points and absorbance-difference diagrams for testing the “Einheitlichkeit” (“uniformity”) of a reaction is discussed by use of the imidazole catalysed hydrolysis of p-nitrophenyl acetate as an example. The analysis was based on kinetic spectra E(λ)t1, t2,..., tn and time dependant absorbance values at various wave lengths E (t) λ1, λ2,..., λm measured preferably in the same reaction vessel. The (pseudo-) first-order rate constants were calculated from the absorbance-time curves E(t))λ by formal integration. The kinetic constants of the various reaction steps were used for digital simulation of the total reaction by an electronic computer. The evaluation methods described need neither extinction coefficients nor experimentally determined E∞ values but make it possible to compute them.