• Vitamin B6 is a collective term for all 3-hydroxy-2-methyl-pyridines with vitamineffects (A): the alcohol form (pyridoxol),which is also called pyridoxine (PN), thealdehyde pyridoxal (PL). and the aminepyridoxamine (PM).
• To denote phosphorylation of metabolitesin position 5, a P is simply attached to thename (PNP, PLP, and PMP, respectively).These six substances all have the samevitamin B6 effects, where as pyridoxic acidhas no known function.
10It is important co enzyme in the intermedullarymetabolism of amino acids and complexglycolipids.It is white crystalline substance soluble inwater and alcohol.
• PLP is a coenzyme for many enzymes,mostly of the amino acid metabolism. PMPalso has coenzyme function, but only fortransaminases. As a coenzyme, PLP isbonded to a lysine R-group of the enzyme.PLP’s aldehyde group and the amino groupof the amino acids react to form a Schiffbase, causing a shift of the amino acid’scharges.
• This activated amino acid can now bedecarboxylated or the side chaineliminated. Glycogen phosphorylase,which is needed to metabolize muscleglycogen, contains PLP, but it is unclearhow it functions.
BIOCHEMICAL FUNTIONS OFPYRIDOXINE:1. As co-transaminase: It acts as acoenzyme in transamination reactions.GOT [AST] and GPT [ALT] aretransaminases which need PLP ascoenzyme for their actions
2. As co-decarboxylase: It also functions asa coenzyme in non-oxidativedecarboxylation of some aminoacids ortheir derivatives.
Tyrosine Tyramine + CO2Histidine Histamine + CO23. As Ala-synthase: in the synthesis of δ-aminolevulinic acid which is anintermediate in heme synthesis
4. As coenzyme in the conversion oftryptophan to niacin.5. Interconversion of glycine and serine byhydroxymethyl transferase.
6. In transulphuration reactions, wheretransfer of-SH group takes place, B6 isneeded.7. In synthesis of sphingosine8. Intramitochondrial fatty acid synthesis9. Intestinal absorption of aminoacids10.Transport of K+. B6 is reported to promotetransport of K+across the membrane.
11.Synthesis of CoA-SH from pantothenicacid needs B6. in B6deficiency CoA level ofthe liver is decreased.12.B6acts as a coenzyme for glycineSynthase.
19Absorption & excretionIt is readily absorbed in the jejunum & ileumof small intestineWidely distributed in various tissues aExcretion – mainly from kidney but smallquantities through feces and sweat
BIOCHEMISTRY PEARLS• Thiamine (vitamin B1) is an important water-soluble vitamin that, in its active form ofthiamine pyrophosphate, is used as acofactor in enzymatic reactions that involvethe transfer of an aldehyde group.
• Thiamine deficiency is uncommon exceptin alcoholics who, as a consequence ofnutritional deficiencies and malabsorption,may become deficient.
• Thiamine classic clinical triad of dementia,ataxia (difficulty with walking), and eyefindings may be seen, but more commonly,only forgetfulness is noted.
• Thiamine pyrophosphate is also animportant cofactor for manydehydrogenase reactions as well as thetransketolase reactions in the pentosephosphate pathway of carbohydratemetabolism.
Anaemia• Hypochromic microcytic anaemia d/treduced heme production.Pyridoxine deficiencies are mostly seen inwomen taking OCPs, alcoholics infantsand those on ATT especially INH
Vitamin B6 Deficiency(Pyridoxine)(Deficiency causes:• Depression (Sadness)• Dizziness (Faintness)• Nausea (Vomiting)• Sores in the mouth• Dizziness (Faintness)
TOXICITY• Large dose of vit b6 cause severe nerve damage.• Two B vitamins that should be avoided are vitaminB15(pangamic acid) and vitamin b17 (laetrile)• Laetrile contains 6% cyanide by weight , and hascaused chronic cyanide poisoning and death.• Too much B-6 in the body can result in nightrestlessness a vivid dream recall.
• More than 200 mg/day cause peripheralneuropathy• Doses higher than 500 mg/day may betoxic, leading to serious central nervoussystem problems, pain in the arms andlegs, a numbness or tingling in the handsand feet, clumsiness, loss of balance, anddifficulty in walking.
• High doses of B-6 can lead to increasedsusceptibility to cadmium toxicity, causeperipheral neuropathy
36MANAGEMENTDepending on severity, dosage up to 100mg /day given.