PH112 Vitamins and Coenzymes PDF

PH112 3 Vitamins and Coenzymes Dr Matthew Ivory  Contents  Introduction  De3ning coenzymes  De3ning vitamins  Classes of vitamins  Vitamin B: B1, B2, B3, B5, B6, B7, B9 & B12  Vitamin C  Vitamin A  Vitamin D: D2 & D3  Vitamin E  Vitamin K: K1 & K2 ...

PH112 3 Vitamins and Coenzymes Dr Matthew Ivory  Contents  Introduction  De3ning coenzymes  De3ning vitamins  Classes of vitamins  Vitamin B: B1, B2, B3, B5, B6, B7, B9 & B12  Vitamin C  Vitamin A  Vitamin D: D2 & D3  Vitamin E  Vitamin K: K1 & K2   To introduce the structures and names of the vitamins in groups A, B, C, D, E & K  To show the relationships between these vitamins and the coenzymes they form AIMS AND OBJECTIVES  To demonstrate the essential functions of vitamins and the consequences of de3ciency disease  To overview the sources of vitamins and our daily requirements Macronutrie Total energy Carbohydrat nts es Fats Protein Micronutrients: Minerals Micronutrients: Vitamins REAL SCENARIO “I read yesterday in the Daily Mail that I will not need my Ou jab this year if I take plenty of Vitamin X – can I have some please” Vitamin boosts may increase death rate of users, report says By Jeremy Laurance, Health Editor 01 October 2004 One in three women and one in four men in the UK take dietary supplements for health reasons. But a review of 14 trials of vitamin pills taken by 170,000 people found they increased the death rate by 6 per cent. While they o[ered no explanation as to what caused the deaths, they discovered that the supplements o[ered no protection against cancers of the gut. The researchers, writing in The Lancet, estimate that for every one million people taking the supplements, 9,000 would die prematurely as a result. The 3gure takes account of the background level of premature death in the population. Two UK experts described the 3ndings as "somewhat chilling". Professor David Forman of the University of Leeds and Douglas Altman of Cancer Research UK says in The Lancet: "The prospect that vitamin pills may not only do no good but also kill their consumers is a scary speculation given the vast quantities that are used in certain communities." Professor Forman said yesterday that supplements could be useful for people such as pregnant women and the elderly, who might be unable to get adequate vitamins from their diet. But they did not oNer a short cut to better health. For the majority of the population who ate a balanced diet, there were no grounds for taking vitamin supplements, he said. Taking large doses of vitamin C or B, beyond what the body can immediately absorb, only creates expensive urine.  Cofactors  Cofactors are often required to activate enzymes. Cofactors Essential ions Coenzymes e.g. Na+, K+ Co-substrates Prosthetic groups (loosely bound) (tightly bound) e.g. ATP, NADH e.g. thiamine pyrophosphate, pyridoxal-5’-phosphate Apoenzyme – the large protein molecule that forms the bulk of the enzyme molecule. In isolation it may be able to bind substrate but not able to catalyse its reaction Cofactor – non-protein molecule or metal ion that binds to the apoenzyme to form the holoenzyme. The cofactor may be bound at the active site or at a distant site on the apoenzyme. Holoenzyme – the catalytically active form of the enzyme. Substrate – the substance upon  The substrate may be able to bind to the apoenzyme but in the absence of the cofactor, no reaction occurs The substrate binds to the holoenzyme and a reaction occurs  Essential Ions  These can act as cofactors to enzymes (e.g. iron ion in peroxidase).  Their intake is therefore vital (see ‘Minerals Reference Intake’ table). Coenzymes  De3nition: A non-protein organic compound, produced in living cells, which is involved in the activation of enzymes. Co-substrates are altered during the course of the reaction and then dissociate from the enzyme. They are then regenerated by another enzymatic reaction.  Prosthetic groups remain bound to the enzyme but still need to be regenerated.  Coenzyme Reactions Coenzyme + A-X Coenzyme-X + A First enzyme Coenzyme-X + B Coenzyme + B-X Second enzyme Unlike enzymes, the coenzyme is often structurally altered during an enzyme-catalysed reaction. In the top reaction, the functional group X is cleaved from molecule A and bound to the coenzyme, producing the active form of the coenzyme (coenzyme-X). Coenzyme-X then acts as a coenzyme for the second enzyme,  A-X Coenzyme B-X First enzyme Second enzyme A Coenzyme-X B In the body, the coenzyme will be regularly regenerated by the 3rst enzyme so that it can act as a coenzyme for the second enzyme multiple times  Vitamins De3nition: General term for any of several organic substances essential for normal metabolic processes and which, when absent in the diet, produce de3ciency states as they are not produced naturally by the body. Many coenzymes are synthesised from dietary precursors - these dietary precursors are often vitamins.  Required for growth, reproduction & normal body function  Lack of vitamins may result in a de3ciency disease  The term ‘vitamin’ was 3rst used in 1912 to describe a ‘vital amine’ derived from rice husks that cured beriberi  Further discoveries were also called vitamins (although not all are amines)  Classes of Vitamins WATER SOLUBLE LIPID SOLUBLE  readily excreted via  stored in the body kidney in urine (usually in liver)  required daily (in  excessive intake can small cause toxicity amounts) e.g. Vitamins A, D, E & K e.g. Vitamins B & C End of Part 1