Enzyme Cofactors and Vitamins PHL – 213 Biochemistry - I Co-enzymes Enzyme Cofactors and Vitamins Dr. Vidya.D Asst. Professor, College of Pharmacy, Prince Sattam Bin Abdul Aziz University, Kingdom of Saudi Arabia

Objectives Definition Classification Features Functions

Enzyme --Cofactors A simple enzyme is an active enzyme that consists only of protein. Many enzymes are active only when they combine with cofactors such as metal ions or small molecules. A coenzyme is a cofactor that is a small organic molecule such as a vitamin.

Enzyme Cofactors (continued)

Coenzymes can be classified by their source 1) metabolite coenzymes synthesized by common metabolites include nucleoside triphosphates most abundant is ATP, but also include uridine diphosphate glucose (UDP-glucose) and S-adenosylmethionine ATP can donate all of its three phosphoryl groups in group-transfer reactions S-adenosylmethionine can donate its methyl group in biosynthetic reactions. UDP-glucose is a source of glucose for synthesis of glycogen in animals and starch in plants.

2) vitamin-derived coenzymes Vitamins are required for coenzyme synthesis and must be supplied in the diet Lack of particular vitamins causes disease There are two catagories of vitamins: 1) water-soluble - B vitamins and vit. C required daily in diet excess excreted in urine 2) lipid-soluble - vitamins A, D, E, K Intake must be limited Stored in fat

Function of Coenzymes A coenzyme prepares the active site for catalytic activity.

Metal Ions as Cofactors Many active enzymes require a metal ion. For example, Zn2+, a cofactor for carboxypeptidase, stabilizes the carbonyl oxygen during the hydrolysis of a peptide bond.

Some Enzymes and Their Cofactors

Salient features of Coenzyme Coenzymes are heat stable. They are low-molecular weight substances. The coenzymes combine loosely with the enzyme molecules and so, the coenzyme can be separated easily by dialysis. When the reaction is completed, the coenzyme is released from the apo-enzyme, and goes to some other reaction site.

Water-Soluble Vitamins Water-soluble vitamins are soluble in aqueous solutions cofactors for many enzymes not stored in the body

Descriptions of Water-Soluble Enzymes

Thiamin (Vitamin B1) Thiamin was the first B vitamin identified is part of the coenzyme thiamin pyrophosphate (TPP) is used to decarboxylate -keto carboxylic acids has a recommended daily allowance (RDA) of 1.2 mg; deficiencies include fatigue, poor appetite, weight loss, nerve degeneration, and heart failure

Riboflavin (Vitamin B2) is found in the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) is needed for good vision and healthy skin has an RDA of 1.2–1.8 mg; deficiencies include dermatitis, dry skin, tongue inflammation, and cataracts

Niacin (Vitamin B3) Niacin is part of the coenzyme nicotinamide adenine dinucleotide (NAD+) involved in oxidation–reduction reactions has an RDA of 14–18 mg deficiency can result in dermatitis, muscle fatigue, and loss of appetite

Pantothenic Acid (Vitamin B5) is part of coenzyme A needed for energy production is involved in glucose and cholesterol synthesis has an RDA of 5 mg deficiency can result in fatigue, retarded growth, cramps, and anemia

Pyridoxine (Vitamin B6) Pyridoxine and pyridoxal are two forms of vitamin B6, which are converted to the coenzyme pyridoxal phosphate (PLP) required in the transamination of amino acids and decarboxylation of carboxylic acids has an RDA of 1.3–2.0 mg; deficiency may lead to dermatitis, fatigue, and anemia

Cobalamin (Vitamin B12) Cobalamin consists of four pyrrole rings with a Co2+ is a coenzyme for enzymes that transfer methyl groups and produce red blood cells has an RDA of 2.0–2.6 μg deficiencies are pernicious anemia, nerve damage, and malformed red blood cells

Ascorbic Acid (Vitamin C) is required in collagen synthesis and healing of wounds has an RDA of 60–95 mg deficiencies are scurvy, weakened connective tissue, slow-healing wounds, and anemia

Biotin Biotin is a coenzyme for enzymes that transfer carboxyl groups has an RDA of 30 g deficiencies include dermatitis, loss of hair, fatigue, and anemia

Folic Acid (Folate) Folic acid (folate) consists of pyrimidine, p-aminobenzoic acid, and glutamate forms the coenzyme THF used in the transfer of methyl groups and is involved in the synthesis of nucleic acids has an RDA of 400  g deficiencies are abnormal red blood cells, anemia, and poor growth

Folic Acid (Folate) (continued)

Fat-Soluble Vitamins Fat-soluble vitamins are vitamins A, D, E, and K soluble in lipids but not in aqueous solutions stored in the body important in vision, bone formation, antioxidants, and blood clotting

Retinol (Vitamin A) Vitamin A is needed for retinol (vision); synthesis of RNA has an RDA of 800  g deficiencies include night blindness, immune system repression, and slowed growth

Cholecalciferol (Vitamin D) Vitamin D (D3) is synthesized in skin exposed to sunlight regulates the absorption of phosphorus and calcium during bone growth has an RDA of 5–10 μg deficiency includes weakened bones

Tocopherol (Vitamin E) is an antioxidant in cells may prevent the oxidation of unsaturated fatty acids is found in whole grains and vegetables has an RDA of 15 mg deficiencies are hemolysis and anemia

Menaquinon (Vitamin K) Vitamin K1 in plants has a saturated side chain. Vitamin K2 in animals has a long unsaturated side chain. Vitamin K2 is needed for the synthesis of zymogens for blood clotting. Vitamin K has an RDA of 90–120 μg. Deficiencies are prolonged bleeding time and bruising

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