F. García Cánovas

Transient phase kinetics of activation of human plasminogen.

Equations for the time-dependent concentrations of all species involved in the general mechanism of human plasminogen activation proposed by Wohl et al. (J. biol. Chem. 255, 2005–2013, 1980) have been derived. These equations are valid for the whole course of the reaction: for both the transient phase and the steady state. In addition, we compare our results with the ones obtained by the above-mentioned authors for the steady state assuming rapid equilibrium conditions. Finally, we propose a method for the determination of all velocity constants.

Kinetics of a general model for enzyme activation through a limited proteolysis

Abstract The kinetics of a general model for enzyme activation through a limited proteoylsis has been studied, and equations which show the dependence on time of the concentration of the products have been deduced. A method for determination of rate constants is proposed, and several other mechanisms have been treated as particular cases of the general model.

Kinetics of the trypsinogen activation by enterokinase and trypsin.

A global kinetic analysis of the mechanisms of the trypsinogen activation by enterokinase and trypsin is presented. The kinetic equations of both the transient-phase and the steady-state of these mechanisms are presented. In addition, we here derive the corresponding kinetic equations for the case in which the condition of rapid equilibrium prevails and we propose a kinetic data analysis. The significance of this approach to the treatment of other zymogen activation processes is discussed.

Kinetics of a model for zymogen activation: The case of high activating enzyme concentrations

Transient phase and steady state equations have been derived for the following enzyme activation mechanism: (formula; see text) in which the concentrations of activating enzyme, E, and substrate, A, are greatly in excess of that of zymogen, Ei. EEi, EEa, EaA and EaY are four intermediates; W is a peptide related from Ei during EEa formation and X and Y are the products of Ea reaction on A. From the general equations, approximate solutions under certain simplifying conditions have been derived. Finally, some formal particular cases of the above mechanism are considered.

Epidermis tyrosinase is a hysteretic enzyme

Abstract 1. 1. Cresolase activity of epidermis tyrosinase activity presents a lag time (τ). 2. 2. The representation of log T versus enzyme concentration is a straight line with a slope equal to — 1. τ values lengthened with increased concentration of substrate, tyrosine. 3. 3. Experimental data is in agreement with a possible dimerization process, similar to other hysteretic enzymes, in which the lag period corresponds to an aggregation step.

Derivation of the transient phase equations of enzyme mechanisms from those of other systems

A simple and general method is presented for the derivation of the transient state equations of any enzyme mechanism which can be considered as a special case of another, more complex system. This method saves mathematical effort and time. In addition, a new classification of the enzyme mechanisms is proposed.

Kinetic characterization of an enzymatic irreversible inhibition measured in the presence of coupling enzymes. The inhibition of adenosine triphosphatase from sarcoplasmic reticulum by fluorescein isothiocyanate

A kinetic study of the irreversible inhibition of an enzyme measured in the presence of a coupling enzyme system has been carried out to assess the type of mechanism of the irreversible inhibition. By using the algebraic criteria proposed here it should be possible to discriminate between these mechanisms and to calculate their corresponding kinetic constants. An experimental design has been developed and applied to fluorescein isothiocyanate as inhibitor of the ATPase activity from sarcoplasmic reticulum.

IV. Transient phase of the Uni-Bi mechanisms

Abstract Different procedures in order to determine the rate constants of the chemical reactions involved in the ordered Uni-Bi (second intermediate with competing nucleophile) and random Uni-Bi mechanisms have been developed from the time-dependent behavior in its transient phase.

Kinetics of the trypsinogen activation by enterokinase and/ or trypsin: Coupling of a reaction in which the trypsin acts on one of its substrates

Abstract A global kinetic analysis of the mechanisms of trypsinogen activation by (a) both enterokinase and trypsin and (b) by trypsin alone is presented. In both cases, the activation is coupled to a monitor reaction, in which the trypsin acts upon one of its substrates. The kinetic equations of both the transient phase and the steady state are derived for these mechanisms. In addition, the corresponding kinetic equations are determined for the cases in which the condition of rapid equilibrium prevails.

II. Transient phase of two-substrate enzyme systems.

Abstract The time dependence in the transient phase of the two-substrate enzyme systems which evolve according to the random ternary-complex, ordered ternary-complex, ping-pong bi-bi and Theorell-Chance mechanisms has been studied. With this purpose, the equations derived in paper I have been applied. This has allowed to propose a method in order to obtain the rate constant values of these enzyme reactions. In addition, we show that, from experimental knowledge of the induction periods of the ligand species, it is possible to give a method which allows to discriminate between these mechanisms.