Co-enzymes are organic compounds which are bound to the enzymes to make them catalytically active. They bind to the enzyme transiently at the time of catalysis and help in the reaction. They also act as co-factors in a number of enzyme catalysed reactions. For examples. Nicotinamide adenine dinucleotide (NAD), Nicotinamide adenine dinucleotide phosphate (NADP), Flavin mononucleotide (FMN), Flavin adeine dinucleotide (FAD) and co-enzyme A (CoA) are important co-enzymes.