Catalytic constant and its unit

The catalytic constant, denoted by kcat, is a measure of the catalytic efficiency of an enzyme. It is defined as the number of substrate molecules that are converted to product by a single enzyme molecule per unit time when the enzyme is saturated with substrate. The unit of kcat is usually expressed in s^-1.

Second order rate constant

The correct answer to the given question is option 'B', which states that the unit of catalytic constant is equal to the second order rate constant.

The second order rate constant is a measure of the rate of a reaction between two reactant molecules, both of which are involved in the rate-determining step of the reaction. It is expressed in units of M^-1s^-1.

Relationship between kcat and k

The relationship between kcat and k, the rate constant, can be explained by the Michaelis-Menten equation, which describes the kinetics of enzyme-catalyzed reactions:

v = (kcat[E][S])/(Km + [S])

where v is the initial velocity of the reaction, [E] is the enzyme concentration, [S] is the substrate concentration, Km is the Michaelis constant, and kcat is the catalytic constant.

In this equation, kcat represents the maximum rate of the reaction when the enzyme is fully saturated with substrate, whereas k represents the rate of the reaction at a given substrate concentration. Thus, kcat is proportional to k, and the units of kcat and k are related by the substrate concentration.

Conclusion

In conclusion, the unit of catalytic constant, kcat, is equal to the second order rate constant, and it is a measure of the catalytic efficiency of an enzyme. The relationship between kcat and k can be explained by the Michaelis-Menten equation, which describes the kinetics of enzyme-catalyzed reactions.