Enzymes - is this correct?

[FROGGBUSTER]

Enzymes that undergo Michaelis-Menten kinetics = single-active sites = competitive binding of inhibitors.

Allosteric enzymes = multiple chains (oligomers) = multiple active sites = Sigmoidal kinetics.


Can I get a verification of this? And is what I wrote always true?

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[zwander]

Yea, Michaelis mentin is definitely just one binding site for a substrate, although that enzyme be subjected to either noncompetitive or competitive. In terms of competitive, Km decreases, but Vmax remains the same. For noncompetitive, there is some sort of irreversible chemical reaction (covalent bond) and a certain portion of enzymes are killed, thus vmax decreases, but Km remains the same.

In terms of sigmoidal binding curves, yes you need more than one substrate, for that first substrate will either promote a second binding like in hemoglobin, or reduce the affinity like in...idk...

 

[salim271]

In terms of sigmoidal binding curves, yes you need more than one substrate, for that first substrate will either promote a second binding like in hemoglobin, or reduce the affinity like in...idk...

like in hemoglobin as well when CO2 is binding and kicking out O2, XD.

 

[zwander]

like in hemoglobin as well when CO2 is binding and kicking out O2, XD.

I don't actually think that's true! A positive Sigmoidal binding curve is representing the shifting from a T-state (tense) to R-state for that same substrate. Essentially the binding of the first O2 in hemoglobin changes the conformation of the transport enzyme making its affinity for O2 greater for the 2nd than it was for the first.

In comparing O2 and CO2, I'm not actually sure how many CO2 can bind hemoglobin. I know only a small fraction of the transport of CO2 from capillaries to lungs is CO2 in plasma, while the major is due to the bicarbonate buffer which releases H+ ions which can then bind hemoglobin. Also I think molecular CO2 has the capacity to bind hemoglobin at the N-terminals on each chain.

But if you are talking about the Bohr effect I think that's correct as in it shifts the hemoglobin curve to the right causing a greater release of O2 at given O2 partial pressure, because it stabilizes the T state.