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What is All are true about Vitamin B|2, except - and explain in detail?
Ans. is 'd' i.e., Requires for conversion of pyruvate to lactate o Active form of vitamin B12 are methylcobalamine and deoxyadenosylcobalamine. Following reactions require vitamin B12 coenzyme:i) Isomerization of methylmalonyl CoA to succinyl CoA : In this reaction, active form of vitamin B12 is deoxyadenosyl cobalamine. Propionyl-CoA is produced as catabolic end product of some alipathic amino acids and b-oxidation of odd chain fatty acids. Propionyl CoA is then converted to succinyl CoA through methyimalonyi-CoA. Thus methylmalonyl-CoA is accumulated and excreted in urine as methylmalonic acid (methylmalonate) in vitamin B12 deficiencyQ, i.e. methylmalonic aciduriaQ.ii) Conversion of homocystein to methionine : - In this reaction, active form is methylcobalamine. This is the only reaction which requires both vitamin B12, (as methylcobalamine) and folic acid (as N2-methyl- H4-folate). The reaction is catalyzed by the enzyme cobalamin-dependent methionine synthase also called 5-methyltetrahydrofolate-homocysteine methyltransferaseQ.iii) Methylation of pyrimidine ring to form thymine.iv) Conversion of ribonucleotides to deoxyribonucleotides in DNA synthesis.v) Required for metabolism of diols :vi) In bacteria for interconversion of glutamate and b methyl asparate