Which of the following vitamins can act without phosphorylation?

Ans. B. LipoamideAll the vitamins listed except lipoamide contain at least one phosphate in their cofactor form. Thiamine (vitamin B1) is converted to thiamine pyrophosphate simply by the addition of pyrophosphate. It is involved in aldehyde group transfer. Niacin (nicotinic acid) is esterified to adenine dinucleotide and its two phosphates to form nicotinamide adenine dinucleotide. Pyridoxine (vitamin B6) is converted to either pyridoxal phosphate or pyridoxamine phosphate before complexing with enzymes. Riboflavin becomes Flavin mononucleotide by obtaining one phosphate (riboflavin 5'- phosphate). If it complexes with adenine dinucleotide via a pyrophosphate ester linkage, it becomes flavine adenine dinucleotide.