According to the solubility of antioxidants, it can be divided into two categories: water-soluble antioxidants and fat-soluble antioxidants. Water-soluble antioxidants are usually found in the cytoplasmic matrix and plasma, while fat-soluble antioxidants protect the lipids of cell membranes from peroxidation. These compounds are either biosynthesized in the human body or ingested through diet. Different antioxidants are distributed in body fluids and tissues in a certain range of concentrations. Glutathione and coenzyme Q10 are mainly found in cells, while other antioxidants such as uric acid are more widely distributed (see the table below for details). Some antioxidants are only present in certain specific body tissues because of their antioxidant effects and also important pathogens and pathogenic factors.
Some compounds coordinate and chelate with transition metals to prevent the metal from catalyzing the production of free radicals in cells, thereby playing a role in antioxidant defense. A particularly important point in this anti-oxidant defense method is to isolate iron ions through coordination chelation, because iron ions are the key to some iron-binding proteins such as transferrin and ferritin. . Selenium and zinc are generally regarded as antioxidant nutrients. These two elements have no antioxidant effect but can play a role in the activity of some antioxidant enzymes.
