Section Bank C/P 96 - Ternary Complex

[jeep1010]

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The answer choice states that a ternary complex forms which is a protein complex with 3 different molecules bound together. Are the three molecules: ATP, Glycerol, and Glycerol Kinase?

 

[aldol16]

Yes.

 

[jeep1010]

@aldol16 So glycerol kinase would not be the ternary complex itself right? it would be part of the ternary complex? Initially i thought the ternary complex was Glycerol, ATP, and the Amino Acid(s)

 

[aldol16]

@aldol16 So glycerol kinase would not be the ternary complex itself right? it would be part of the ternary complex? Initially i thought the ternary complex was Glycerol, ATP, and the Amino Acid(s)

Yeah, so it's always important when answering these type of questions to ask yourself if you're answering the right question. Glycerol kinase is the enzyme that performs the reaction. But binary and ternary complexes refer to complexes that are formed along the reaction coordinate. That is, A, B, and C are in unbound states at the beginning of the reaction coordinate. Then they come together and bind. How they bind at this stage determines whether it's ordered or not. In this case, B comes in first and binds to A. Then C comes in and binds. This forms the ternary complex that's at another point in the reaction coordinate. The reaction then occurs and you get another intermediate where you have enzyme and product bound. Then in your products, at the end of the reaction coordinate, enzyme and product are in unbound states again.

 

[jeep1010]

@aldol16 I am re-doing the section banks, and I got this question right again but I wanted to know what exactly makes up the ternary complex here? Ternary complex is defined as three components bound together. For this case is the ternary complex composed of: Glycerol Kinase (GK), Glycerol and ATP?

 

[aldol16]

Yes, in this case, the ternary complex would be GK, ATP, and glycerol. The enzyme is GK and the co-substrates are ATP and glycerol. All three components come together to form the ternary complex, which then reacts.

 

[deleted647690]

Hm, I had no idea what this question was talking about when I did it. I vaguely remember covering complexes of this sort in biochem? This definitely wasn't covered in my review books. What topic would this be called? Enzyme catalysis mechanisms?


So a ternary complex involves an enzyme and 2 reactant substrates, while a binary complex involves an enzyme and one reactant substrate?

I tried to look up catalytic enzyme mechanisms online, but I just found stuff about covalent catalysis and acid-base catalysis

 

[aldol16]

Hmmm, I don't know. Perhaps enzyme kinetics? It would be included in any rigorous treatment of enzyme kinetics.

 

[deleted647690]

Hmmm, I don't know. Perhaps enzyme kinetics? It would be included in any rigorous treatment of enzyme kinetics.

So then I guess an enzyme substrate conformation is referred to as a binary complex, and then any additional cofactors/coenzymes that bind create a ternary complex....ah yes I remember now this is related to ping pong mechanisms. That's where this was from

 

[aldol16]

So then I guess an enzyme substrate conformation is referred to as a binary complex, and then any additional cofactors/coenzymes that bind create a ternary complex....ah yes I remember now this is related to ping pong mechanisms. That's where this was from

Yeah, generally speaking, ternary complexes are not common in chemistry - so much so that a basic treatment of kinetics usually glosses over it because it usually doesn't happen. If you think about it, it's quite disfavorable to have ternary complexes since two molecules have to come together first and then wait for the next one to react - they don't react by themselves. So you get no enthalpic stabilization from new bonds formed and you lose a lot of entropy because the two molecules now have to be held together. The other way you can get a ternary complex is if three molecules collide at the same time, but the chances of that are super super low as to be negligible.

 

[deleted647690]

Yeah, generally speaking, ternary complexes are not common in chemistry - so much so that a basic treatment of kinetics usually glosses over it because it usually doesn't happen. If you think about it, it's quite disfavorable to have ternary complexes since two molecules have to come together first and then wait for the next one to react - they don't react by themselves. So you get no enthalpic stabilization from new bonds formed and you lose a lot of entropy because the two molecules now have to be held together. The other way you can get a ternary complex is if three molecules collide at the same time, but the chances of that are super super low as to be negligible.

So then it follows that ternary complexes formed by ordered mechanisms are even less likely than those not formed sequentially. Thanks!

 

[aldol16]

So then it follows that ternary complexes formed by ordered mechanisms are even less likely than those not formed sequentially. Thanks!

Ordered here just means that there is a specific order that the co-substrates bind. This is way more likely than both substrates coming together at the same time. Because then, both the space and time dimensions must coincide.