Kinetics of the transient-phase and steady-state of the monocyclic enzyme cascades

This paper presents a kinetic analysis of the whole reaction course, i.e. of both the transient phase and the steady state, of open multicyclic enzyme cascade systems. Equations for fractional modifications are obtained which are valid for the whole reaction course. The steady state expressions for the fractional modifications were derived from the latter equations since they are not restricted to the condition of rapid equilibrium. Finally, the validity of our results is discussed and tested by numerical integration. Apart from the intrinsic value of knowing the kinetic behaviour of any of the species involved in any open multicyclic enzyme cascade, the kinetic analysis presented here can be the basis of future contributions concerning open multicyclic enzyme cascades which require the knowledge of their time course equations (e.g. evaluation of the time needed to reach the steady state, suggestion of kinetic data analysis, etc.), analogous to those already carried out for open bicyclic cascades.

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Kinetics of the Transient Phase or Pre-Steady-State Phase of Enzymic Reactions

A Study of Enzymes: Volume I Enzyme Catalysis, Kinetics, and Substrate Binding ◽

10.1201/9780429291579-12 ◽

2019 ◽

pp. 377-412

Author(s):

Stephen A. Kuby

Keyword(s):

Steady State ◽

Transient Phase ◽

Kinetics Of

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Kinetic analysis of mechanism of intestinal Na+-dependent sugar transport

AJP Cell Physiology ◽

10.1152/ajpcell.1985.248.5.c498 ◽

1985 ◽

Vol 248 (5) ◽

pp. C498-C509 ◽

Cited By ~ 23

Author(s):

D. Restrepo ◽

G. A. Kimmich

Keyword(s):

Experimental Data ◽

Steady State ◽

Sugar Transport ◽

Enzyme Kinetic ◽

Steady State Distribution ◽

State Distribution ◽

Least Squares Fit ◽

Coupling Stoichiometry ◽

Rate Limiting ◽

Kinetics Of

Zero-trans kinetics of Na+-sugar cotransport were investigated. Sugar influx was measured at various sodium and sugar concentrations in K+-loaded cells treated with rotenone and valinomycin. Sugar influx follows Michaelis-Menten kinetics as a function of sugar concentration but not as a function of Na+ concentration. Nine models with 1:1 or 2:1 sodium:sugar stoichiometry were considered. The flux equations for these models were solved assuming steady-state distribution of carrier forms and that translocation across the membrane is rate limiting. Classical enzyme kinetic methods and a least-squares fit of flux equations to the experimental data were used to assess the fit of the different models. Four models can be discarded on this basis. Of the remaining models, we discard two on the basis of the trans sodium dependence and the coupling stoichiometry [G. A. Kimmich and J. Randles, Am. J. Physiol. 247 (Cell Physiol. 16): C74-C82, 1984]. The remaining models are terter ordered mechanisms with sodium debinding first at the trans side. If transfer across the membrane is rate limiting, the binding order can be determined to be sodium:sugar:sodium.

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