thank you so much!

Is this a homework problem? It is up to you to provide your answer (or at least make an attempt) before we help you. A good place to start on this problem is to give a few examples. It might also help to differentiate between delta-G and delta-G°'.

No, I'm studying for an exam and I meant free gibs energy a.k.a delta-G°. and I dis not understand whether It's always beneath 0 (so it's a spontaneous reaction) for all regulatory enzymes or not.

When delta-G is less than zero, a reaction is spontaneous, and when delta-G = 0, a reaction is at equilibrium. When delta-G° is negative, a chemical reaction has an equilibrium constant that is greater than one. This symbol, delta-G°, refers to standard state, meaning all reactants and products at 1 M in concentration. The two quantities do not provide the same information, and their values are often not the same number. That having been said, the in vivo values of delta-G are more difficult to obtain because one has to know the concentrations of reactants and products in vivo. If they are not available, one has no choice but to use delta-G° values in one's arguments.

 

I think that "always" is a high bar, meaning that there could well be exceptions to any generalization. I would start by taking regulatory enzymes from glycolysis and gluconeogenesis (hexokinase, PFK-1, pyruvate kinase, pyruvate carboxylase, PEPCK, fructose 1,6-bisphosphatase, and glucose 6-phosphatase) and finding the values of Gibbs' free energy in a biochemistry textbook. Nelson and Cox or Metzer are my go-to sources, typically.

Edited July 8, 20178 yr by BabcockHall

The equilibrium constant for aspartokinase is not particularly favorable, but it is heavily regulated in E. coli.

Edited July 18, 20178 yr by BabcockHall