Metabolism of 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside triphosphate and its nucleoside precursor in the erythrocytes.

We recently discovered new nucleotides (4-pyridone-3-carboxamide-1-beta -D-ribonucleoside phosphates) in human erythrocytes. To establish the precursor compound and pathways of nucleotide derivative formation and breakdown, human erythrocytes were incubated for 3 hours with 0.3 mM 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside (4PYR) and erythrocyte concentrations of 4PYR and adenine nucleotides were followed. 4PYR triphosphate increased from 16.1 +/- 0.6 micro M to 74.9 +/- 9.17 and 4PYR monophosphate increased from 5 micro M to 254.7 +/- 13.9 micro M. Conversely, incubation with 0.3 mM 4-pyridone-3-carboxamide (4PY) did not lead to additional 4PYR nucleotide formation. 4PYR nucleotides were catabolized to 4PYR. We conclude that 4PYR nucleotides are formed in erythrocytes by nucleoside kinase-mediated 4PYR phosphorylation and catabolized by 5'nucleotidase-mediated dephosphorylation.