These types of free radicals are mainly produced by cellular enzymes such as NADPH - oxidase, myeloperoxidase and nitric oxide synthase (NOS). (mdpi.com)
Tet2 is a type of cellular enzyme known as an epigenetic regulator — responsible for making specific chemical annotations to regions of DNA that alter the activity of many different genes. (ucsf.edu)
Other cellular enzymes shepherd the dross to the cell's disposal machinery, called proteasomes. (sciencemag.org)