Plasma ADP levels: direct determination with luciferase luminescence using a biometer

A method is described for the determination of low plasma levels of adenosine-5'-diphosphate (ADP) using a Dupont Biometer to measure luminescence produced by the luciferin-luciferase reaction. Endogenous ATP is removed by incubation with luciferase. The remaining ADP is then quantitated, following its conversion to ATP, after incubation with creatine phosphate and creatine kinase. The mean coefficient of variation for 0.02 and 2.2 micromol/liter ADP standards were 2.1 and 1.8% respectively. The method has been applied to human and rabbit plasma. Human plasma ADP concentrations were found to be 0.13 +/- 0.025 (10) micromol/liter and rabbit plasma concentration were 0.07 +/- 0.05 (5) micromol/liter. Several other possible applications of the method are discussed.