Km and Vmax

[docntrainin]

I read previous threads about the relationship and significance of Km and Vmax and how noncompetitive and competitive inhibitors affect them. Does the addition of a catalyst affect either of these values in a predictable way i.e. is there some rule that I should know? Thanks!

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[inaccensa]

I read previous threads about the relationship and significance of Km and Vmax and how noncompetitive and competitive inhibitors affect them. Does the addition of a catalyst affect either of these values in a predictable way i.e. is there some rule that I should know? Thanks!

Isnt the enzyme that we are talking about a catalyst? its not used in the reaction

 

[docntrainin]

Isnt the enzyme that we are talking about a catalyst? its not used in the reaction

Yeah, I think I was just confused about what exactly kcat is and how to calculate it. Is that just the rate constant of a catalyst and is it somehow related to Km and Vmax?

 

[tn4596]

Yeah, I think I was just confused about what exactly kcat is and how to calculate it. Is that just the rate constant of a catalyst and is it somehow related to Km and Vmax?

ummm...we shud know this for mcat?...
i never learned about any of this till biochem...well w/e..here is it straigh outta my book:

These are quantities related to the reaction between enzyme and its substrates. simply put

E + S => ES => P + E

P= product, E = enzyme. S = substrate. ES= enzyme substrate complex

Vmax is just the maximum velocities of the reactions.

Km is the is the substrate concentration, where the reaction velocities is at half-maximal (so in relation to vmax, it is the concentration of substrates at 1/2 Vmax. )

kcat is the catalytic constant, which determine the efficiency of an enzyme ( the higher the kcat, the more efficient the enzyme). kcat = Vmax/ [E]t

[E]t = concentration total , is the sum of concentration of the concentration of enzyme [E] and the concentration of the enzyme-substrate complex [ES]. so [E] + [ES] = [E]t

About how these are affected by nonpetitive and competitive inhibitor, lets just say they altered the Michealis-Menten equation and show up differently on a Lineweaver-Burk plot...I know for sure this is out of the scope of mcat, cuz there is no way i am going to memorize all of these equations agains...

 

[MSU2009]

Adding more substrate will reduce the effects of competitive inhibition; is this perhaps what you meant by adding "catalyst"?

 

[docntrainin]

Okay, I can't remember where but I did have some practice MCAT question about Km, Vmax, and kcat. I just didn't really understand the relationship with kcat but now that you described it as an increase in kcat = increase in enzyme efficiency, that makes sense.

 

[inaccensa]

Adding more substrate will reduce the effects of competitive inhibition; is this perhaps what you meant by adding "catalyst"?

Substrate does not equal catalyst. Enzyme is a catalyst, the classic definition of a species that is not used up in a reaction. Substrate and a competitive inhibitor have similar structures and compete to bind with the enzyme, the reason being, the enzyme has an affinity to bind to lets say something.. If it binds to a substrate, you get a product but if it bind to an inhibitor, there is no resultant product.

 

[tn4596]

When you are refering to biological enzyme reactions and use these value, you are using the Michealis-Menten model, which assume [ES] or Enzyme substrate complex concentration and [E], enzyme concentration; is constant during the course of the reaction. Therefore, any mentioning of adding more enzyme will discrupt this model, and we can only talk about modifying the concentration of the substrate. The concentration of the substrate is seen is the X value in ur typical XY graph, and the velocities of the reaction is seen is the Y vaue. In a sense, substrate concentration is the independent and reaction velocities is the dependent.

Since, competitive inhibitor bind to the Enzyme, increasing the substrate concentration will reduce the effect of the inhibitor since you can out compete the inhibitor.

For uncompetitive inhibitor, the inhibitor bind to the Enzyme-Substrate complex (which is AFTER the substrate had bind onto an enzyme), therefore increasing Substrate concentration won't reduce the inhibitor effect.

Noncompetitive (or mix inhibition), the inhibitor bind to both Enzyme and Enzyme Sbustrate complex, increasing substrate concentration still wont affect inhibition.

 

[MSU2009]

Substrate does not equal catalyst. Enzyme is a catalyst, the classic definition of a species that is not used up in a reaction. Substrate and a competitive inhibitor have similar structures and compete to bind with the enzyme, the reason being, the enzyme has an affinity to bind to lets say something.. If it binds to a substrate, you get a product but if it bind to an inhibitor, there is no resultant product.

Hence the quotes around catalyst....