If an enzyme-mediated reaction were carried out at a temperature that was higher or lower than optimal, the vmax for the reaction would probably be

The vmax would be decreased.

Explanation:

Since enzymes are also proteins, factors such as pH, temperature and substrate concentration will influence their performance. Enzymes, like all proteins, are denatured under certain conditions and stop working, or have the Vmax of their reactions diminished.

Thus, the vmax of an enzymatic reaction increases to some extent with increasing temperature. From a certain optimum temperature (whose value depends on the enzyme that is reacting), where the reaction speed is maximum, protein denaturation occurs, which inactivates the enzyme. This is because there is a change in its three-dimensional shape, so the enzyme can no longer attach to the substrate and catalyze the chemical reaction. Thus, after passing the optimum temperature, the reaction Vmax decelerates rapidly.