Generation of inorganic pyrophosphate from extracellular adenosine triphosphate by human serum and plasma

Objective. To quantify inorganic pyrophosphate (PP i ) production from extracellular adenosine triphosphate (ATP) by human serum or plasma. Methods. Serial measurements of ATP hydrolysis (t 1/2 ) were performed by the luciferase method from a starting concentration of 1 μM in serum or platelet-poor plasma incubated under physiologic conditions. ATP was then pumped into another sample of each specimen using the rate constant derived from the ATP t 1/2 of that specimen. Trace ( 32 P) gamma ATP was added at the start of the infusion ; conversion to ( 32 P) inorganic orthophosphate (Pi) and to ( 32 P) PP i was determined by precipitation of P i as reduced phosphomolybdate before and after treatment with yeast pyrophosphatase. Results. ATP was hydrolyzed by all serum and plasma specimens ; the rate of hydrolysis in serum and plasma from the same blood sample was nearly identical. PP i was the major product, averaging 71%. Conclusion. PP i is the major product of ATP catabolism in serum and platelet-poor plasma.