Antioxidant protection system

Humans have evolved a highly sophisticated and complex antioxidant protection system against ROS. It involves both endogenous and exogenous components that function interactively and synergistically to neutralize free radicals.

Endogenous Antioxidants

1. Bilirubin
2. Thiols, e.g., glutathione, lipoic acid, N-acetyl cysteine
3. NADPH and NADH
4. Ubiquinone (coenzyme Q10)
5. Uric acid

Enzymes:

1. copper/zinc and manganese-dependent superoxide dismutase
2. iron-dependent catalase
3. selenium-dependent glutathione peroxidase
4. heme oxigenase (HO)

Dietary Antioxidants

1. Vitamins (C,E)
2. Beta carotene, oxycarotenoids, e.g., lycopene and lutein
3. Polyphenols, e.g., flavonoids, flavones, flavonol’s

Metal Binding Proteins

1. Albumin (copper)
2. Ceruloplasmin (copper)
3. Metallothionein (copper)
4. Ferritin (iron)
5. Myoglobin (iron)
6. Transferrin

Figure 3: Outline of various sources of reactive oxygen species and action of antioxidant enzymes

In the next sections antioxidant enzymes will be discussed detailed.