The effects of the molecular environment on the kinetics of catalase reaction and its relevance to cell aging

Abstract

Catalase-mediated oxygen evolution from H 2O 2 was measured with a Clark electrode in a closed, buffered aqueous medium in a properly designed experimental model. Addition of various molecules (bovine serum albumin, egg albumin, dextrane, starch and PEG-8000) in increasing concentrations up to greater than 20% by volume decreased the rate of oxygen evolution in a linear fashion, although there were some quantitative differences between the effects of various components. The rotational correlation time of the spin label TMPN in BSA and egg albumin increased considerably in both protein solutions indicating a very significant increase of the microviscosity of these media. The results are interpreted in terms of the molecular enzyme kinetic model (MEKM) predicting that apart from microviscosity, the average mass distribution and the distance of the nearest two lattice points formed by components of the medium are also inversely proportional to both the forward and backward rate constants of the formation of the enzyme-substrate complex. These observations, on one hand, lend further experimental support to the MEKM and on the other one, are consistent with the membrane hypothesis of aging which explains the loss of cell functions by an age-dependent increase of intracellular density.