When Km value for an enzyme is low, its affinity is considered to be high for its substrate. Considering this concept, does it mean that high affinity always leads to high product formation? Or is there a possibility that high affinity can actually even decrease product formation as ES complex may require more energy to break?
Affinity can be considered as capability of recognizing the specific substrate or how strongly the enzyme binds with the substrate. If we consider the first case, then we can say it must not influence/Negatively influence the break down energy of ES complex. When, an enzyme strongly binds with substrate, it can spare more energy to break ES complex thus leading to lower production. So, pattern of binding side can be an interesting topic to find out a solution for it.
Regards
Nayem Zobayer
No not so obviously. Enzymes with high Km's can be much faster in reaction velocity. Think of it as also rate of release of product when affinity is high. For e.g. if products also bind strongly their release will be slower. The Km kind of tells you the concentration of substrate required to give a particular velocity. IF two enzymes are HAVE THE SAME VELOCITY, then a low Km enzyme requires less substrate concentration than a high Km enzyme for a given reaction velocity.
Thus for comparing two enzymes the ratio of kcat/Km is used - it is more of an overall "efficiency" measure than simply kcat alone or Km alone. The constant Kcat is a measure the rate of catalysis and = Vmax/Et Et = total enzyme concentration.
@Prem - If two enzymes have the same Vmax, then the Km by the definition being the substrate concentration at which half of the Vmax would be reached, should have the same value isn't it
Ah ha... I did not say Vmax ! I SHOULD have used the word "initial" velocity, instead of just velocity. ;-)
Look at the attached figure of two enzymes reaching the same Vmax. Is Km1 = Km2??
If you remember V0 initial velocity (y-axis) is not same as Vmax when enzyme is completely saturated... (top of curve) Let me know if I need to explain fully, I will be glad !!!
You can also have product inhibition, if the substrate's affinity or as I would call it, structural features that make it high binding, carries over to some degree in the product. Then you would not get high product formation. This is true for S adenosylmethionine synthase, and probably many other enzymes. The Km is not just a function of the first step of E+ S to ES on and off rate. It is also ES rate of going to EP. So if P and S compete for E, and P binds well to E and doesn't want to get released, you get product inhibition.
if Km is less, stronger binding affinity for the substrates . If two enzymes are present in which on enzyme have less Km and more affinity than other , this more affinity enzymes produce more product .
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