enzyme kinetics

[akimhaneul]

So the general equation for enzyme reaction is this..

E+S <-> ES -> E+P

Is there a reason why E+P can't go back to ES?

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[theonlytycrane]

It's just an irreversibility assumption used in the model when substrate concentration is much greater than product concentration.

 

[akimhaneul]

It's just an irreversibility assumption used in the model when substrate concentration is much greater than product concentration.

Then why is E+S to ES reversible?

 

[aldol16]

Then why is E+S to ES reversible?

The assumption is that binding in biological systems is generally reversible (if you can't unbind something from the enzyme, it will shut down the enzyme - i.e. an inhibitor that binds irreversibly). E + P goes back to ES could in theory occur and actually does occur in practice for many enzymes (most of the enzymes in the glycolytic pathway run in reverse during gluconeogenesis). When you're talking about enzyme kinetics, you can make a simplifying assumption that it is not reversible if the reaction is only going one way biologically (e.g. gluconeogenesis does not occur under well fed conditions). This helps when you do an actual kinetic calculation (which is generally beyond the scope of most undergraduate courses).