How are enzymes regulated directly?

Enzymes can be influenced by other molecules which either increase or diminish their effectiveness. Molecules that enhance enzyme activity are known as activators, while those that decrease enzyme activity are called inhibitors. Additionally, certain enzymes have allosteric sites separate from their active sites. When specific molecules (allosteric regulators) bind to these sites, they can either activate or inhibit the enzyme's activity. This binding induces a conformational change in the enzyme that affects its catalytic activity. A third method is covalent modification. In this process, enzymes are altered by adding or removing molecules to either activate or inhibit them. A common form of covalent modification involves the addition or removal of phosphate groups by kinases and phosphatases, respectively. For example, checkpoint kinase 2 (CHK2) plays a vital role in the DNA damage response by adding phosphate groups to proteins involved in DNA repair, thus activating them.