Metabolism of Guanosine in Human Erythrocytes

Abstract

The metabolism of guanosine in human erythrocytes has been studied in two different experimental systems - direct incubation and dialysis incubation - the latter allowing continuous addition and removal of substances. Intra- and extracellular purine compounds were analyzed using high-performance liquid chromatography (HPLC). At 37 °C, a normal pH (7.4) and a favorably high concentration of inorganic phosphate, guanine nucleotides were synthesized at a substance rate of about 0.17 mmol • h^-1 (calculated per liter erythrocytes) when guanosine was kept at a concentration of 25 µmol • l^-1. At a higher guanosine concentration the rate of synthesis increased only moderately. Erythrocytes loaded with guanylates lost these nucleotides at a rate of 0.023 mmol • h^-1 at a normal phosphate concentration and somewhat slowlier at a higher phosphate concentration. The metabolism kept the guanylates in an equilibrium that was similar to the equilibrium between the adenylates.

Preparation and Preservation of Red Cells

“…A problem is that even with storage media which give a comparatively high initial, intracellular pH, the resulting higher glycolysis rate causes an increased formation of acid metabolites so that the situation during the 5-6th week will not be very much different. In the PAGGS-S/M AS the formation of guanine nucleotides seems to give some improvement due to the fact that GTP can substitute for ATP in some functions [59]. In Erythro-Sol the elevating effect on the intracellular pH together with the availability of adenine and phosphate promotes the maintenance of both ATP and 2,3-DPG; a stock of adenylates is built up at the early phases of storage.…”

CDP-Choline Does Not Inhibit Erythrocyte Glycolytic or Pentose Phosphate Pathway Enzyme Activity

“…CTP inhibited G6PD competitively with glucose-6-phosphate (K; = 1.7 mmol/1 CTP) and non-competitively with NADP (K; mmol/1 CTP) [5]. Since the intraerythrocytic concentration of CTP ranges from 0.77 to 1.74 mmol/1 [2,3] in P5Nase deficiency and since the intraerythrocytic concentration of NADP (~ 1 pmol/l) is below its Km of ap-7.8 activity, as well. Thus, the physiologic signif icance, if any, of an increased intraerythrocytic concentration of CDP-choline remains to be determined.…”

“…Torrance and Whittaker [9] originally de scribed an unidentified cytidine compound(s) of approximately 1 mmol/1 concentration in the RBC in P5Nase deficiency. Subsequent studies by Ericson et al [3] and Swanson et al [2] have identified increased concentra tions of CDP-choline (0.93-1.51 mmol/1) in the P5Nase-deficient erythrocyte. Paglia et al [1] found a CDP-choline concentration of 0.31-0.45 mmol/1 in their case of unex plained hemolytic anemia.…”

“…Cytidine diphosphocholine (CDP-choline) is a pyrimidine 5'-nucleotide derivative that is normally found in trace concentra tions in the mature erythrocyte [1,2], An increased concentration of CDP-choline is observed in the red blood cells (RBC) of indi viduals with hereditary hemolytic anemia due to pyrimidine 5'-nucleotidase (P5Nase, EC 3.1.3.5) deficiency [2,3]. In addition, Paglia et al [1] have recently described a case of chronic hemolytic anemia associated only with increased RBC CDP-choline content and normal P5Nase activity.…”