Michaelas Constant

 Michealas Constant (K_m ) is the affinity between an enzyme and a substrate. It is the halfway point of V_max , or V_max/2. 

K_m is inversely proportional to the affinity between an enzyme and a substrate. The higher the K_m, the lower the affinity. 

Finding K_m

Finding K_m on a Michealas-Menten graph

Changes in K_m due to enzyme inhibition

K_m may change due to inhibition of enzymes. Different kinds of inhibition leads to different changes in Km.

Competative Inhibition

During competative inhibition, the inhibitor binds to the active site of the enzyme, as it has a very similar structure to the substrate, and prevents enzyme-substrate complexes from forming. K_m is increased as the inhibitors lower the affinity of the enzyme for substrates, as the enzymes tend to have affinity for the inhibitors.

Non-competative Inhibition

During non-competative inhibition, the inhibitor binds to an allosteric site of the enzyme, changing its active site and making the active site uncompatible to substrates. K_m does not change because the inhibitors do not bind to the active site.

Uncompetative Inhibition

During uncompetative inhibition, the inhibitor binds to the enzyme-substrate complex. To maintain the equailibrium between enzyme and enzyme-subtrate complex,more substrates bind to enzymes. Lower concentrations of substrates are needed to form half the maximum concentration of enzyme-substrate complex, so K_m is decreased.