The nicotinamide coenzymes and CoA play an important role in the metabolism of lipids as in β-oxidation of fatty acids and ketone body formation. The suggested function of NADH and CoA diphosphatases are: regulation of the size of CoA and nicotinamide coenzyme pools in different subcellular compartments, elimination of non-functional oxidized CoA and NAD+/NADH which may accumulate in the oxidizing environment of the peroxisomes and mitochondria, where there is a high level of oxidative stress. NADH diphosphatases are the only source for generation of NMNH inside the cell. The presence of multiple genes with the same enzymatic activity in different subcellular compartments in evolutionary diverse organisms suggests that these genes are associated with a specific biological function. This applies to the NADH and CoA diphosphatases. NADH and CoA diphosphatases are present in both peroxisomes and mitochondria. So the NADH and CoA diphosphatases act to regulate and hydrolyse the non-functional nucleotides and so protect the other subcellular compartments e.g. the cytoplasm from these oxidized nucleotides; this indicates the importance of compartmentalization.