Michaelis-Menten Constant (Km value & Its Significance), Lecture notes of Biochemistry

Download Michaelis-Menten Constant (Km value & Its Significance) and more Lecture notes Biochemistry in PDF only on Docsity!

Michaelis-Menten Constant

(Km value & Its Significance)

In an enzyme catalyzed reaction when there is large excess of substrate and the enzyme concentration is held constant, if substrate concentration (S) is plotted against velocity (V) or reaction rate, a hyperbolic curve is obtained (see figure). This type of plot is also known as saturation plot.

In this situation addition of more substrate will not increase reaction rate because all the active sites of the enzyme are saturated with substrate molecules and the rate of reaction will increase only by addition of more enzyme.

Michaelis constant is a reflection of the affinity of enzyme for its substrate and is characteristic of a particular enzyme-substrate system. The smaller the value of Km, the more strongly the enzyme binds the substrate.

Kinetic values of enzyme catalyzed reactions are usually measured under steady state conditions and described by a simple expression called Michaelis-Menten, equation. V = Vmax [S] / Km+ [S] where, V → velocity or reaction rate V max → maximum velocity or maximal reaction rate S → Substrate concentration Km → Michaelis constant.

Km Values for Some Enzymes with Respective Substrates

Significance of Michaelis-Menten Constant: (i) By knowing the Km value of a particular enzyme-substrate system, one can predict whether the cell needs more enzymes or more substrate to speed up the enzymatic reaction. (ii)If an enzyme can catalyze a reaction with two similar substrates (e.g., glucose and fructose) in the cell, it will prefer that substrate for which the enzyme has lower Km value.

Source:

1. Plant Physiology by Taiz & Zeiger (2015)
2. Biochemistry by Stryer (2016)