Concentration of Substrate

Concentration of Substrate

When the amount of enzyme, temperature and pH are all kept constant, increasing the concentration of substrate at first increases the rate of the enzyme-catalysed reaction almost proportionally, because more substrate molecules are available to occupy the enzyme's active sites at any given moment. As substrate concentration keeps rising, however, the rate of increase slows down, and eventually the reaction rate levels off at a maximum value, called Vmax, beyond which adding still more substrate makes no further difference. This levelling off happens because, at high substrate concentration, essentially every enzyme molecule present already has a substrate bound in its active site; the enzyme is said to be saturated, and the overall rate is then limited only by how quickly each enzyme molecule can process the substrate it is holding, not by how much substrate is available. …