Oxypurine cycle in human erythrocytes regulated by pH, inorganic phosphate, and oxygen.
The effect of pH, PO2, and inorganic phosphate on the uptake and metabolism of hypoxanthine by erythrocytes has been studied. Uptake of hypoxanthine and accumulation of inosine 5'-monophosphate (IMP) were markedly increased at acid pH, high external phosphate concentrations, and low PO2. Release of accumulated IMP as hypoxanthine occurred at alkaline pH values and low external phosphate concentrations. Conditions favoring IMP accumulation gave rise, in the absence of hypoxanthine, to a corresponding increase in 5'-phosphoribosyl-1-pyrophosphate. Intracellular phosphate concentrations were markedly pH dependent and a model is presented whereby hypoxanthine uptake and release are controlled by intracellular concentrations of inorganic phosphate and 2,3-bisphosphoglycerate. These allosteric effectors influence, in opposing ways, two enzymes governing IMP accumulation, namely 5'-phosphoribosyl-1-pyrophosphate synthetase and 5'-nucleotidase. These metabolic properties suggest that the erythrocyte could play a role in the removal of hypoxanthine from anoxic tissue.
Berman
P A
PA
Department of Chemical Pathology, University of Cape Town Medical School, South Africa.
Black
D A
DA
Human
L
L
Harley
E H
EH
D000244:Adenosine Diphosphate / Q000097:blood; D000255:Adenosine Triphosphate / Q000097:blood; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007042:Hypoxanthines / Q000097:blood*; D007291:Inosine Monophosphate / Q000097:blood; D010100:Oxygen / Q000097:blood* / Q000502:physiology; D010313:Partial Pressure; D010710:Phosphates / Q000097:blood / Q000494:pharmacology*; D010754:Phosphoribosyl Pyrophosphate / Q000096:biosynthesis
D007042:Hypoxanthines; D010710:Phosphates; D007291:Inosine Monophosphate; D000244:Adenosine Diphosphate; D010754:Phosphoribosyl Pyrophosphate; D000255:Adenosine Triphosphate; D010100:Oxygen