Kinases add - groups to other enzymes. This activities some enzyme while inhibiting other

Kinases refer to the group of enzymes which catalyze the transfer of phosphate group to their substrate. The phosphate group is usually transferred from high energy phosphate donating molecules such as ATP and GTP.

Addition of phosphate group may activate some proteins or enzymes while it may deactivate other enzymes.

For example, CDK-activating kinase adds phosphate groups to the CDK in order to activate them.