The antioxidant defence system – Part 2
Enzyme antioxidant defence system
Mineral antioxidant defence system
Enzymes are protein products produced in the body and their function is to catalyze chemical reactions.
These enzymes are usually produced in the body and because they are proteins, amino acids, which are building blocks of protein, are used in their production.
The main enzymes in this group of antioxidants are Superoxide dismutase; Glutathione peroxidase; and Catalase.
1. Superoxide dismutase – SOD
This is an enzyme that alternately catalyses the reaction that converts the superoxide free radical (O2-) to an oxygen molecule (O2) or hydrogen peroxide (H2O2). The superoxide radical is one of the most destructive free radicals in the body. Hydrogen peroxide, which is released during the metabolism of oxygen in cells, also damages the cells, but it is degraded by the enzyme catalase – the third enzyme in the Enzyme Antioxidant Defense System.
2. The glutathione peroxidase
This is a group of enzymes of the peroxidase family. The group is made up of about eight sub-groups of enzymes. The different sub-groups function in different parts of the body.
Five of such groups have been extensively studied by researchers and their findings are as follows:
The first sub-group, GP-1 is found in almost all the cells of the body.
GP-2 is found mainly in the cells of the intestines and in the extracellular fluid.
GP-3 is located mainly in the plasma.
GP-4 is also found in all the cells of the body.
GP-5 is an androgen-related protein in the epididymal cells of the testicles.
All these peroxidase enzymes catalyze the conversion of hydrogen peroxide to water and oxygen. They are also involved in the conversion of lipid hydroperoxide to their corresponding alcohol. In all of these reactions, they protect the tissues in the parts of the body where they are found against oxidative stress.
Catalase: This enzyme catalyses the reaction that breaks hydrogen peroxide to water and oxygen. By this function, catalase prevents the accumulation of the peroxide free radical and the damage it would have wrecked on the cells and tissues.
Catalase is found in the liver (especially bovine liver) and some microorganisms. Another food source of catalase is sweet potatoes. The trace element that functions with catalase is iron.
Trace minerals: Certain minerals required in very minute amounts take part in the enzymatic reactions involving the antioxidant enzyme defense system. These trace minerals are zinc, copper, and magnesium, which are co-factors in the reactions that the superoxide dismutase enzyme catalyzes. Selenium is a co-factor in the glutathione peroxidase enzyme reactions.
Iron is involved with catalase. These co-factors are also limiting factors for the completion and rate of the chemical reactions.
In other words, in the absence of these co-factors, the chemical reactions catalyzed by the different enzymes will be hindered. These are reactions that seek to either neutralize free radicals or transform them into less harmful or harmless elements or compounds. If these minerals are deficient, there will be an accumulation of free radicals and widespread destruction of tissues of the body by oxidative stress.
Sources of trace minerals: Copper: Cocoa, whole grains, wheat bran, sunflower seeds, and cashew nuts. Others are seafood and organ meat.
Zinc: Oysters, red meat, groundnuts, almonds, chickpeas, dairy products, such as milk and cheese.
Magnesium: Leafy green vegetables, whole grains, Brazil nuts, almonds, hazelnuts, avocadoes, bananas, black-eyed peas, lima beans, and soybeans.
Iron: Leafy green vegetables, soy foods, meat, chicken, eggs, and beans. Selenium: Tuna, shrimps, salmon, sardines, cod, chicken, turkey, asparagus, barley, and brown rice. Other sources are flaxseed, spinach, cabbage, garlic, and broccoli.
Summary of sources of vitamins that are found in the antioxidant defense system
Plant sources of vitamin E include Vegetables: spinach, kale and collard greens. Nuts: almonds, pistachios, pecans, walnuts and hazelnuts. Seeds: pumpkin seeds, sunflower seed, and sesame seed. Fruits: avocado. Seafood/fish: shellfish, shrimps, crayfish, oysters, salmon, and herring. Oils: olive oil, wheat germ oil, sunflower oil, grape seed oil, canola and corn oil.
Vitamin C. Sources of Vitamin C: Fruits: citrus fruits, tomatoes, strawberries, pawpaw, and mangoes. Vegetables: Brussels sprouts, lettuce, spinach, potatoes and cruciferous vegetables such as cabbage, cauliflower, and broccoli. Red and green peppers also contain Vitamin C.
Vitamin A. Sources of vitamin A include Vegetables: carrots, dark green leafy vegetables such as spinach, kale, Mustard greens, Collard greens, Turnip greens, beet greens, and broccoli. Other types of vegetables that are high in vitamin A are Romaine lettuce, pumpkin, sweet red, yellow and green peppers, and peas. Fruits: mango, pawpaw (papaya), cantaloupe melon, dried apricots, and squash. Fish/seafood: tuna, mackerel, and oysters.
Oils: cod liver oil. The three enzymes of the enzyme antioxidant defense system are also produced in the body. Deficiencies of these enzymes are rare.