Question

1-Describe and explain the relationship between number of carriers and V_max.

2-Describe and explain the relationship between number of carriers and K_m.

Answer 1

1. Each type of carrier protein has one or more specific binding sites for its substrate. It transfers the substrate across the lipid bilayer by undergoing reversible conformational changes that alternately expose the substrate-binding site first on one side of the membrane and then on the other. When the carrier is saturated (that is, when all substrate-binding sites are occupied), the rate of transport is maximal. This rate, referred to as V_max, is characteristic of the specific carrier and reflects the rate with which the carrier can flip between its two conformational states.

2.  Each transporter protein has a characteristic binding constant for its substrate, K_m, equal to the concentration of substrate when the transport rate is half its maximum value. As with enzymes, the binding of the substrate can be blocked specifically by either competitive inhibitors (which compete for the same binding site and may or may not be transported by the carrier) or noncompetitive inhibitors (which bind elsewhere and specifically alter the structure of the carrier).