Nucleated Red Cells: Comparative Glycolytic Metabolism and Function

Abstract

The aims of these experiments reported in this thesis were to characterize the red blood cells of healthy wild caught reptiles, in particular crocodilian, determine the presence of enzymes of glycolysis and test the efficiency of crocodilian erythrocytes in reducing methaemoglobin. The composition of crocodilian blood is typical of that of vertebrates in general, with an MCHC close to that of humans, and a packed cell volume of 25% which is typical of reptiles. A haemoglobin electrophoretic pattern of one major band was found in two species of crocodiles, 'C. porosus' and 'C. johnstoni'. Blood glucose levels in the crocodile were similar to human levels, but the levels of lactate were high and variable, consistent with the metabolism of an animal dependent upon anaerobic glycolysis for major activity.The level of red cell ATP is high, similar to those of rabbits; but red cell 2,3-DPG is present in low concentration. Glutathione, an alternative method of modifying the oxygen affinity of haemoglobin, was considerably higher in reptilian red cells compared to human cells, but lower than that found in chickens. Activities of several enzymes of the glycolytic pathway, and several enzymes involved in maintenance of red cell integrity were measured and partially characterized. HK and 6-PGD activities were the lowest among the glycolytic enzymes and could be rate-limiting steps. HK and LDH were both substrate inhibited at high concentrations, while HK and PK activities were strongly affected by pH. Low levels of methaemoglobin and high levels of NADH-MR were found in several reptilian species. In vitro reduction of methaemoglobin with glucose and especially lactate was shown in crocodilian, snake and chicken red cells. These studies have characterized crocodilian red cells and shown that these erythrocytes possess a functional glycolytic pathway, and are capable of maintaining haemoglobin in a reduced state.