<prompt> All are true about Vitamin B2, except -Active form is methylcobalamineRequires for conversion of homocysteine to methionineRequires in metabolism of methylmalonyl Co ARequires for conversion of pyruvate to lactate  <response>: 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 