FINAL PHASE OF ENZYME-REACTIONS FOLLOWING A MICHAELIS-MENTEN MECHANISM IN WHICH THE FREE ENZYME AND OR THE ENZYME-SUBSTRATE COMPLEX AVE UNSTABLE/

An important kinetic analysis of unstable enzyme systems was carried o ut by Duggleby (Duggleby, R.G. (1986) J. Theor. Biol. 123, 67-80). Thi s author states that his results are of general validity in the sense that the instability rate constants may have any value. Later, Wang an d Tsou (Wang and Tsou (1990) J. Theor. Biol. 142,531-549) rediscovered Duggleby's results when they analyzed a scheme in which the inactivat ions were due to a non-complexing irreversible inhibitor, pointing out the need to assume an initial steady-state in the catalytic route of the reaction. In the present contribution we show that there are value s of the instability rate constants for which the equations of Duggleb y are not applicable. We propose, for these cases, an alternative equa tion, which relates the final substrate concentration with the initial ones of both the substrate and the enzyme. Based on this, an experime ntal design for the evaluation of kinetic parameters is suggested. The present work concerns enzyme reactions evolving according to a Michae lis-Menten mechanism, in which the free enzyme and/or the enzyme-subst rate complex are unstable.