Types of biochemical reactions

Question

1)  What type of function that gives the fraction of receptor bound as a function of the concentration of ligand can be derived from the expression for the equilibrium constant of the binding reaction?

 

 

2)  The formula above has one parameter and one independent variable i.e [L]. What is the meaning of the parameter? What does the parameter correspond to under ideal conditions?

 

 

3)  In biochemical systems, the vast majority of transformation reactions are catalyzed by enzymes. Therefore, their kinetics involve the kinetics for formation of enzyme:substrate complexes. Describe how the kinetics of an enzyme catalyzed reaction may be regarded as an extension of the kinetics of a binding reaction. 

 

Thank you so much!

 

Answer 1

1). Fraction of receptor bound vs ligand concentration

The fraction of receptors occupied by a ligand is described by a hyperbolic binding function:

\theta = \frac{[L]} {K_ d + [L]}

where:

θ = fraction of receptors bound

[L] = ligand concentration

K d = dissociation constant

As ligand concentration increases, more receptors become occupied until saturation is reached.

2). Meaning of the parameter (K d)

K d represents the affinity between the receptor and ligand.

Low K d → strong binding (high affinity)

High K d → weak binding (low affinity)

Under ideal conditions, Kd is the ligand concentration at which 50% of the receptors are occupied.

3) Relationship between enzyme kinetics and binding reactions

Enzyme-catalyzed reactions begin with substrate binding:

E + S \right left harpoons ES \right arrow E + P

where:

E = enzyme

S = substrate

ES = enzyme–substrate complex

P = product

The formation of the ES complex follows the same principles as a binding reaction. Therefore, enzyme kinetics can be viewed as an extension of binding kinetics, with the additional step of converting substrate into product.

Enzymes first bind their substrates, then convert them into products. So enzyme reactions are essentially binding reactions followed by catalysis.