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

Objective: To quantify inorganic pyrophosphate (PPi) production from extracellular adenosine triphosphate (ATP) by human serum or plasma.
Methods: Serial measurements of ATP hydrolysis (t1/2) were performed by the luciferase method from a starting concentration of 1 microM 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 t1/2 of that specimen. Trace (32P) gamma ATP was added at the start of the infusion; conversion to (32P) inorganic orthophosphate (Pi) and to (32P) PPi was determined by precipitation of Pi 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. PPi was the major product, averaging 71%.
Conclusion: PPi is the major product of ATP catabolism in serum and platelet-poor plasma.