enzyme question confusing me, please help

[angli524]

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I was actually going over TBR chem book and a passage on michaelis-menten kinetics came up. It says the ES complex is classified as an "intermediate" and not a transition state, which I thought would be correct since enzymes lower the activation energy of the transition state. TBR says since ES complex is detectable by spectroscopy its not a TS. Could someone further explain the logic here?

 

[lookuphere]

I was actually going over TBR chem book and a passage on michaelis-menten kinetics came up. It says the ES complex is classified as an "intermediate" and not a transition state, which I thought would be correct since enzymes lower the activation energy of the transition state. TBR says since ES complex is detectable by spectroscopy its not a TS. Could someone further explain the logic here?

ES complexes are not transition states because transition states are not factored into kinetic equations (i.e. rates).

the ES complex is an intermediate because it is considered part of the reaction rate. transition states are VERY SHORT-lived, thus are not detectable by spectroscopy. Since it is detectable, it has to be either a reactant, product, or intermediate. Hope this helps

 

[werd]

an intermediate is a chemical structure which exists for some amount of time during a chemical reaction, but is neither a reactant or product. if you do tricky experiments you can slow down or stop a rxn at a certain point and isolate the intermediate. intermediates are more stable than either the transition state forming it or the transition state getting rid of it, so they are troughs between two peaks on an energy diagram.
a transition state is the chemical structure as it occurs between intermediates. usually, one bond half formed / the other half broken. the difference is that transition states can't be isolated and are really never stable.

on one of those energy diagrams, peaks are typically transition states and troughs within a rxn are intermediates. below (if it comes out) the two peaks are transition states and the trough in between them is an intermediate...


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