Vitamins and Coenzyme Functions-II Serkan SAYINER, DVM PhD. Assist. Prof. Near East University, Faculty of Veterinary Medicine, Department of Biochemistry [email protected] Water-Soluble Vitamins Vitamin C and B-complex Vitamins 3 Water-Soluble Vitamins ■ They are in different structures. ■ Small quantities serve as coenzymes in important reactions in metabolism (B-complex vitamins). ■ This group includes vitamin C and B-complex vitamins. ■ They are synthesized by plants and microorganisms. ■ Animals often can not synthesize quantities to meet tissue needs. ■ Mammalian store them at very low levels; insignificant. It is therefore necessary that they are continuously supplied by microorganisms in the food, liquid or gastrointinal tract. 4 Vitamin C (Anti-Scurvy Vitamin, Ascorbic Acid) ■ Overview; – It is a powerful reducing agent that participates in several important hydroxylation reactions. – Na+-coupled transporters help to facilitate entry of vitamin C into cells. – Glial cells in the brain regenerate vitamin C from DHA. – It is needed for collagen, carnitine, catecholamine, and bile acid biosynthesis. – Oxalate is a natural degradation product of vitamin C. – It uses Fe++ and Cu++ as cofactors, and it enhances intestinal Fe++ absorption. – It’s deficiency can result in "scurvy." – Although most mammals can synthesize vitamin C from glucose, it cannot be formed in primates, fish, flying mammals, songbirds, or the guinea pig. – It is a natural preservative added to pet food products. 5 Vitamin C (Anti-Scurvy Vitamin, Ascorbic Acid) ■ Scurvy, a vitamin C deficiency disease known since ancient times, was a particular problem for sailors in the 15th-19th centuries, who's diets were often less than adequate on the long voyages they endured. – These men would develop swollen legs blotched with capillary hemorrhages, decaying peeling gums with loose teeth, decreased capacity to heal wounds, depression, anemia, and fatigue. – Infantile scurvy (also known as Barlow's syndrome or disease), is associated with similar symptoms. ■ Although most vertebrates can synthesize vitamin C from glucose, it cannot be formed in primates, fish, flying mammals, songbirds, or the guinea pig. Because in these organisms there is no L- gulonolactone oxidase enzyme. Therefore, these animals require it in their diet. 6 7 Vitamin C is synthesized through the uronic acid pathway in carbohydrate metabolism. 8 Vitamin C ■ Ascorbic acid is found in plant and animal foods. ■ In fruits such as lemon, orange, grapefruit, grape, strawberry, blackberry, banana, melon, watermelon, rosehip, tomatoes, green peppers, cabbage, fresh potatoes and all green-leaved vegetables are rich sources. ■ On the other hand, animal foods are poor sources. ■ If vitamin C rich foods are stored against heat or stored for a long time, they lose their vitamins content significantly. 9 Vitamin C ■ Ascorbic acid is colorless, odorless, sour flavor. ■ Although it is soluble in water and alcohol, it is insoluble in benzene, ether and fats. ■ Its solutions are acidic. ■ The vitamin-based solutions, which are highly stable in crystalline form, are rapidly degraded by air and light. ■ Solvents which are highly resistant to strong acid environments are resistant to neutral and alkaline environments. Contanct with metals and air, and also increase in ambient temperature accelerates its oxidation. ■ The ascorbic acid, a monosaccharide derivative in the keto lactone structure shown by the C6H8O6 closed formula, resembles simple sugars with six carbons in terms of structure. 10 Vitamin C: Functional Groups Ester Hydoxyl Grup C=C Double Bond 11 Vitamin C ■ Ascorbic acid has two isomers, L and D. ■ The L form, which is active in animals and humans, can easily be oxidized and converted into dehydro-L-ascorbic acid (DHA) by giving two hydrogens in vivo. Conversion is reversible. ■ The dehydro L form of vitamin and the dehydro-L-ascorbic acid have an activity of only 80% than L form. ■ The ability of these two forms to convert into one another gives ascorbic acid its redox mediator. 12 Vitamin C ■ Ascorbic acid is dehydroascorbic acid without entering the cell, it takes the form of ascorbic acid after entering the cell. ■ Orally taken vitamins are mostly absorbed by active transport from small intestines and passive transport at a small ratio. ■ When the vitamin taken from the body is transported to the blood, it is destroyed as much as CO2 and H2O as it is in some monosaccharides. ■ In ruminants, oral vitamin C is rapidly degraded by alkaline pH and microflora effect of rumen. Vitamins taken by mouth are therefore not taken into account when meeting the vitamin C requirements. 13 Vitamin C ■ Regardless of whether vitamin C is derived through the diet or from biosynthesis in liver (as in rodents), or the kidneys (as in reptiles), specific transport mechanisms are required to move it into dependent tissues. ■ Ascorbate enters cells via Na+-coupled vitamin C transporters (SVCT 1 or SVCT 2), and cellular efflux occurs by as yet undescribed mechanisms. ■ The oxidized form of vitamin C (dihydroascorbate-DHA), is thought to exit and enter cells via glucose transporters (GLUT 3 and GLUT 1), respectively. ■ In the CNS, glial cells regenerate vitamin C from DHA via reduced glutathione (GSH) oxidation, and then vitamin C is transported back into neurons. – Neurons exhibit a high level of oxidative metabolism, and thus require protection by this important water-soluble vitamin. 14 ? ? ? 15 Functions of Vitamin C ■ Functions are; – Powerful reducing agent (Antioxidant). – Enhance intestinal Fe++ absorption. – Reduce cataract formation. – Enhance leukocyte activity. – Participate in Cu++-dependent amidation reactions in polypeptide hormone biosynthesis (e.g., GH, CT, and MSH). – Participate in the amidation of C-terminal glycine residues in the brain by Cu++- dependent enzymes. – Act as a carrier of sulfate groups in glycosaminoglycan formation (the "ground substance" between cells in all organs). – Participate in hydroxylation reactions using O (with Fe++ or Cu++ as cofactors). • Hydroxyproline and hydroxylysine formation during collagen biosynthesis. • Carnitine biosynthesis from lysine and S-adenosylmethionine. • Dopamine hydroxylation during catecholamine biosynthesis. • Hydroxylation of steroid hormones, aromatic drugs, and carcinogens in liver microsomes. 16 Functions of Vitamin C ■ At the molecular level, ascorbate is a powerful reducing agent, like the fat-soluble vitamin E and as such possesses general importance as an antioxidant, thus affecting the body's "redox" potential. ■ It is used as a natural preservative in pet food products. ■ It is sometimes given to cats as a treatment to reverse the methemoglobinemia associated with acetaminophen toxicity. ■ The physiologic importance of vitamin C as an antioxidant has been documented in pond turtles. – They contain Vitamin C at high concentration in their brains. – These animals exhibit a high tolerance for O2 depletion during diving. – Vitamin C may help to prevent oxidative damage to neurons during the reoxygenation period following a hypoxic dive. 17 Functions of Vitamin C ■ Other reactions involving Vitamin C include hydorxylation using molecular oxygen (O2), that also use either Fe++ or Cu++ as a cofactor. ■ Ascorbate is thought to play either of two roles in hydroxylation. 1. As a direct source of electrons for the reduction of O2, 2. As a protective agent for maintaining Fe++ or Cu++ in their reduced states. ■ Particularly important are hydroxylations involving hydroxyproline and hydroxylysine formation during collagen biosynthesis in connective tissue – The formation of collagen is important during growth and development, – Once physical maturity is achieved, there is relatively little collagen turnover; An exception is healing from tissue injury and scar formation. 18 19 Functions of Vitamin C ■ Vitamin C has a secondary function in connective tissue metabolism as a carrier for sulfate groups needed in glycosaminoglycan formation (i.e. chondroitin sulfate, dermatan sulfate). – These compounds help to form the gel matrix (or "ground substance") between cells in all organs. – There would seem to be an obvious connection between these needs for ascorbate in connec-tive tissue metabolism, and the basic symptoms of scurvy above ■ Although vitamin C supplementation is not considered to be essential in dogs, megadoses of ascorbate fed to the bitch during pregnancy, and provided to the offspring until young adulthood, have been associated with reducing the incidence of canine hip dysplasia in animals considered genetically at risk for this condition. – Newfoundland, Danua, Saint Bernard, Golden and Labrador Retriever, Mastiff, German Shepherd Dog etc. 20 Species: Canine Breed: Hybrid (Golden?) Sex: Male Weight: 45 kg Date of Birth: February 08, 2014 Diagnosis: Right leg hip dysplasia (right coxafemoral dysplasia) Source: Neu Animal Hospital 21 Diagnosis: Right leg hip dysplasia (right coxafemoral dysplasia) Source: Prof. Dr. Deniz SEYREK-İNTAŞ 22 Functions of Vitamin C ■ Vitamin C is also used in the biosynthesis of carnitine from lysine and S-adenosylmethionine. – Carnitine is involved in the transport of long-chain fatty acids across mitochondrial membranes. ■ Vitamin C is active in hepatic microsomal drug metabolism. – Both endogenous and exogenous steroids are hydroxylated and conjugated in the liver, as are certain nonsteroidal drugs (e.g., barbiturates) and suspected carcinogens. – The resulting hydroxylation makes these compounds more