Fatty acid activation, inorganic pyrophosphatase

The ATP is converted to AMP and pyrophosphate (PPi), which is cleaved by pyrophosphatase to two inorganic phosphates (2 Pj). Because two high-energy phosphate bonds are cleaved, the equivalent of two molecules of ATP are used for fatty acid activation. 

Activation of the fatty acid thus requires two ATP equivalents, because the high energy of inorganic pyrophosphate (PP,) is not recoverable. It is hydrolyzed to phosphate by a ubiquitous enzyme called pyrophosphatase. 

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