Question

In simple M-M kinetics, the units of kcat are s–1. Discuss how the units are consistent with the name “turnover number.” If kcat is large, what does that imply about the enzyme? Discuss the term catalytic efficiency; what does it mean for an enzyme to be efficient? How is it consistent with the term for catalytic efficiency (kcat /Km)? Discuss the contribution of the terms kcat and KM to the overall term of catalytic efficiency.

Discuss the meaning of enzyme reaction mechanism in the context of catalysis. How does the study of enzyme kinetics relate to reaction mechanism?

Answer 1

In enzyme kinetics, we are interested to know how many number of molecules of substrate can be converted into product per catalytic site of a given concentration of enzyme per unit time.

• kcat = Turnover number,
• Vmax = Maximum rate of reaction when all the enzyme catalytic sites are saturated with substrate and
• Et =Total enzyme concentration or concentration of total enzyme catalytic sites.

The units of Turn over number (kcat) are kcat = (moles of product/sec)/ (moles of enzyme) or sec^-1.

The term TON represents the the speed with which reactants can be converted into products in a given time

If Kcat is large the rate of conversion of reactants into products is very high

Catalytic efficiency: The ability of an enzyme to convert reactants into products in unit time. An enzyme with high catalytic efficiency can convert a large number of substrate molecules into products in unit time

k_cat/K_M is the rate constant that measures catalytic efficiency. This measure of efficiency is helpful in determining whether the rate is limited by the creation of product or the amount of substrate in the environment.

If Kcat is larger than Km, a greater proportion of substrate will be converted into products i.e., catalytic efficiency is high

If Kcat is smaller than Km, a lower proportion of substrate will be converted into products i.e., catalytic efficiency is small

Enzyme reaction mechanism: It is the way of representation that shows how the reactants are converted to products.

The study of enzyme kinetics gives the information about on which terms of reactants the reaction depends and that data relates to the mchanism of the reaction.