2.8—Core Practical 4 - enzyme-catalysed reaction rate

To investigate temperature, pH, enzyme concentration or substrate concentration, measure the initial rate of an enzyme reaction while changing one independent variable and controlling the others.

Use equal volumes, a defined mixing time and a signal that changes predictably, such as colour, gas volume or product concentration. Take several early readings, calculate a gradient and repeat at each condition.

Initial rate avoids later distortion when substrate is depleted or product accumulates. A water bath, buffer and matched enzyme volumes make the comparison fair.

A rate–temperature curve rises while collisions become more frequent, reaches an optimum and falls when the protein begins to lose structure. A plateau with increasing substrate may indicate that active sites are saturated.

A final colour or total gas volume is not automatically a rate. State the proxy, time interval, controls and uncertainty before interpreting the pattern.