Question

When analyses enzyme-kinetics, what can we know with Michaelis-Menten equation? Write down everything you can.

Answer 1

Answer :

Michealis-Menten enzyme kinetics equation is one of the best known model of enzyme kinetics.  It was proposed and explained by German biochemist Leonor Michaelis and Canadian physician Maud Menten.

Increase in the substrate concentration increases the velocity of enzyme reaction gradually within the limited range of substrate levels. When plotted on a graph, these two parameters result in a rectangular hyperbola.

The graph for the Michealis-Menten equation is as given below followed by explanation :

When enzyme (E) binds to substrate (S), they form an unstable intermediate ES-complex, before the formation of product (P) and release of enzyme (E)
E + S ⇌ ES → P + E
The k₁ , k₂ and k₃ are the velocity constants of the reactions   E + S ⇌ ES , the reversible reaction and ES → P + E respectively.

The Michealis-Menten constant is given by the formula
K_m = (k₂ + k₃) / k₁

After algebraic manipulations, we get the formula
V = ( V_max x [S] ) / ( K_m + [S] )
where
V is measured velocity
S is substrate concentration
V_max is maximum velocity
K_m is Michealis-Menten constant

K_m, the Michealis-Menten constant is defined as the substrate concentration expressed in moles per liter to produce half of the maximum velocity. This can proven by substituting V by ( V_max / 2 ) in the Michealis-Menten equation, It indicates that only half of the enzyme molecules are bound to the substrate when its concentration equals the K_m value.

K_m value is constant and an important characteristic feature of any given enzyme. A low K_m value indicates a strong affinity between enzyme and substrate and a high K_m value reflects a weak affinity. Most of the enzymes have K_m values in the range of 10-5 to 10-2 moles. K_m value is independent of concentration of enzyme.

The graph plotted for the Michealis-Menten equation was a rectangular hyperbola as mentioned earlier and was difficult to extrapolate. Therefore, Lineweaver-Burk double reciprocal plot was proposed which gave a straight line when reciprocals of substrate concentration and velocity against each other. This was easier to interpret and determine the K_m value.

The Lineweaver-Burk plot is as given below :