Pretend scientist discover an enzyme in the human body that works best at 39 degrees Celsius. What process would this enzyme most likely be involved in?

The normal body temperature for humans is 37 degrees Celsius. Most of the enzymes of a human's bodywork best at this temperature. If an enzyme was discovered which works best at 39 degrees Celsius, then it means that the enzyme works at elevated temperatures for events which require slightly higher temperatures.

The enzyme will most probably work for overcoming fever or for reducing the temperature of the body after exercise.