Studies on IMP degradation and ribose 1-phosphate utilization in human erythrocytes.
1. Intact human red cells do not attack exogenous IMP. The nucleotide is readily broken down by the soluble erythrocyte fraction to inosine, hypoxanthine and ribose 1-phosphate, with a pH optimum of approx. 6.2. 2. Ribose 1-phosphate can be actively reutilized, in the presence of ATP and hypoxanthine, to give IMP, at pH 7.4. The velocity of the IMP salvage synthesis dramatically increases at more alkaline pH values. 3. The two curves relating the velocities of IMP breakdown and of IMP synthesis as a function of hydrogen ion concentration intersect at pH 7.4. 4. The observations might be relevant in the process of purine transport by red cells.