Discussed and non-discussed in this website

This website is centered on the steady-state kinetics of enzyme-modifier interactions. It deals with reversible reactions of systems in which all enzyme-containing complexes are set up rapidly on the steady-state time scale upon reactant mixing. In other words, progress curves, typically product concentration or any property proportional to it against time, show neither a burst, nor or a lag.

Seventeen reversible basic modifier mechanisms belong here. They will be introduced, discussed and analyzed with hints on how to treat raw experimental data and fine-tuning the calculation of kinetic parameters.

Several of the basic mechanisms can show up with different attributes, notably progress curves that are non-linear on the steady-state scale and can show either a burst or a lag. The burst or lag, consisting of a single or a double exponential progress, can be followed by a linear steady-state in reversible, slow-onset inhibition and activation, or can decline to a straight line with zero slope in enzyme inactivation (= irreversible inhibition). Note that enzyme inactivation can also show a straight line resembling the steady-state of a reversible reaction if the ‘irreversible’ final enzyme-modifier complex decays, generally slowly, regenerating free enzyme.

Any tight-binding condition in reversible enzyme-modifier complexes is not a property that deserves a treatment at the level of mechanism, since this is simply an experimental issue discussed in Tightly-bound modifiers. Tight-binding of modifier to enzyme can be present in ‘fast’ reactions and in slow-onset inhibition/activation.

Originally, this website was planned to contain also enzyme inactivation (irreversible inhibition), which can exhibit specific, catalytic and mixed character and can be linear, but also hyperbolic. In a paper for readers with a flair for mathematics [1], Christopher Topham succeeded in creating an extension of the Botts-Morales general modifier mechanism [2], to include stable and unstable irreversible inhibitors, and unstable activators.
Also originally planned for this website was a treatment of reversible, slow-onset enzyme-modifier interactions with their manifold facets.

After seeing the growth of the website, it was decided not to include these topics because of the large space required, being impossible to omit vital details. However, the interested reader will find a full account of enzyme inactivation and reversible slow-onset interactions elsewhere. In the referenced book, users find support for experimental design, for the interpretation of raw data, and analytical dichotomous keys for the identification of mechanisms.


References

  1. Topham CM (1990) A generalized theoretical treatment of the kinetics of an enzyme-catalysed reaction in the presence of an unstable irreversible modifier. J Theor Biol 145: 547-572.
  2. Botts J, Morales M (1953) Analytical description of the effects of modifiers and of enzyme multivalency upon the steady state catalyzed reaction rate. Trans Faraday Soc 49: 696-707.

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