Adenine nucleotide metabolism of blood platelets: III. Adenine phosphoribosyl transferase and nucleotide formation from exogenous adenine

Abstract

1. 1. The metabolism of [8- 14C]adenine and [ 14C 2]glycine added to platelet-rich plasma, washed platelets in saline and platelet lysates has been investigated. 2. 2. All the [8- 14C]adenine added was taken up by platelets either in plasma or saline and converted to its nucleotides. Neither platelets nor plasma contained adenine aminohydrolase and an observed extracellular formation of radioactive hypoxanthine was taken to be a measure of adenine nucleotide catabolism of platelets. 3. 3. Adenine uptake by intact platelets was a saturable process and inhibited by adenosine. 4. 4. Platelet lysates contained adenine phosphoribosyl transferase with the following properties: divalent cations are necessary but not inhibitory at high concentrations, an apparent double pH optimum, inhibition by ATP, but not by SH-blockers. AMP formation from adenine and 5- P-Rib- P- P is irreversible, yet AMP and pyrophosphate are inhibitory. In platelet lysates the K m for adenine is 5.2 μM and that for 5- P-Rib- P- P is 5.4 μM. 5. 5. 5- P-Rib- P- P was not synthesized from ATP and Rib-5- P in platelet lysates. 6. 6. [ 14C 2]Glycine was not incorporated in platelet adenine nucleotides indicating that synthesis de novo of purine nucleotides in platelets is absent.