Biology Forums - Study Force

14. Which of the following is a defining characteristic of an allosteric protein demonstrating sequential kinetics?
a. The enzyme interconverts between the T and R states in the absence of substrate.
b. In the enzyme complex, monomeric units might be in a mix of R and T states.
c. The binding of substrate increases the affinity of the complex for additional substrate molecules
d. Once a substrate binds to the R state, all of the monomeric units are "locked" into the R state.
e. The substrate binds only to the monomers previously converted to the R state.

I'm not sure if the the correct answer is b or c (I do not think the other suggestions are correct). It is the induced fit protocol vs completely conformational change concerning substrate binding I am not certain about. See link: (http://en.wikipedia.org/wiki/Allosteric_regulation)

I'd go with c. They don't say anything about substrate binding for b. In the absence of substrate all of the enzyme is in the T state for sequential allostery. The only way you could have a mix of R and T states is if the R states have substrate bound to them.

Thank you. But it says "enzyme complex" i.e. ES. Assumption: So if this ES-complex is located at an R-state, answer b) could be correct. Maybe both b and c are correct answers? By the way, thank you very much.

I interpreted "enzyme complex" to mean just two or more monomers in a complex. You can make a case for b, though c I think is always true.