Adenosine metabolism in human erythrocytes: A study of some factors which affect the metabolic fate of adenosine in intact red cells in vitro

Abstract

Adenosine metabolism was studied in intact human erythrocytes over a range of adenosine and intracellular phosphate concentrations. The concentration of adenosine greatly influenced its partition between deamination via adenosine deaminase (EC 3.5.4.4.) and phosphorylation via adenosine kinase (EC 2.7.1.20). For example, for cells incubated in a medium containing 1 m m phosphate, a single addition of 40 μ m adenosine was largely deaminated (91% deaminated, 9% phosphorylated). Adenosine added to the incubation at lower concentration (0.5 μ m) was largely phosphorylated (81% phosphorylated, 19% deaminated). This partition could be predicted from the known K m and V parameters of the kinase and deaminase reactions. Intracellular phosphate concentrations also affected the metabolism of adenosine, apparently by stimulating adenosine kinase activity in situ. The ratio of adenosine phosphorylated to adenosine deaminated was increased significantly by increases in the intracellular phosphate concentration. Thus, at 4 μ m adenosine, approximately 30% of the adenosine was phosphorylated when the intracellular phosphate concentration was 1 m m. However, when the intracellular phosphate concentration was increased to 7.5 m m, the proportion of 4 μ m adenosine phosphorylated increased to 70%. Our studies also revealed that the kinase was inhibited by high adenosine concentrations, especially when 50–100 μ m adenosine was added to the incubation.