Abstract
In a comparative study of erythrocyte metabolism of vertebrates, the specific activity of glucose-6-phosphate dehydrogenase (G6PD) of the Brazilian opossum Didelphis marsupialis in a hemolysate was shown to be high, 207 +/- 38 IU g-1 Hb-1 min-1 at 37 degrees C, compared to the human erythrocyte activity of 12 +/- 2 IU g-1 Hb-1 min-1 at 37 degrees C. The apparent high specific activity of the mixture led us to investigate the physicochemical properties of the opossum enzyme. We report that reduced glutathione (GSH) in the erythrocytes was only 50% higher than in human erythrocytes, a value lower than expected from the high G6PD activity since GSH is maintained in a reduced state by G6PD activity. The molecular mass, determined by G-200 Sephadex column chromatography at pH 8.0, was 265 kDa, which is essentially the same as that of human G6PD (260 kDa). The Michaelis-Menten constants (Km: 55 microM) for glucose-6-phosphate and nicotinamide adenine dinucleotide phosphate (Km: 3.3 microM) were similar to those of the human enzyme (Km: 50-70 and Km: 2.9-4.4, respectively). A 450-fold purification of the opossum enzyme was achieved and the specific activity of the purified enzyme, 90 IU/mg protein, was actually lower than the 150 IU/mg protein observed for human G6PD. We conclude that G6PD after purification from the hemolysate of D. marsupialis does not have a high specific activity. Thus, it is quite probable that the red cell hyperactivity reported may be explained by increased synthesis of G6PD molecules per unit of hemoglobin or to reduced inactivation in the RBC hemolysate.
Highlights
Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme in the redox metabolism of most cells, and of red cells, which are highly susceptible to oxidative damage
During a comparative study of red cell metabolism in vertebrates, we have observed serendipitously that G6PD activity is very high in a red cell hemolysate of the South-American opossum Didelphis marsupialis
A similar relationship of red cell G6PD activity to hemoglobin has been reported for another South-American opossum, Didelphis aurita [1] and in other Australian marsupials [2], not as high as in D. marsupialis
Summary
Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme in the redox metabolism of most cells, and of red cells, which are highly susceptible to oxidative damage. During a comparative study of red cell metabolism in vertebrates, we have observed serendipitously that G6PD activity is very high in a red cell hemolysate of the South-American opossum Didelphis marsupialis. A similar relationship of red cell G6PD activity to hemoglobin has been reported for another South-American opossum, Didelphis aurita [1] and in other Australian marsupials [2], not as high as in D. marsupialis.
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