Abstract
It is well established that erythrocyte 2, 3-diphosphoglycerate (2, 3-DPG) decreases markedly in diabetic ketoacidosis and returns to a normal level following insulin treatment. However, the cause of the marked decrease remains unknown. Alterations in glycolysis in erythrocytes of patients with diabetic ketoacidosis were investigated by enzymatic analysis of glycolytic intermediates and adenine nucleotides, and the following results were obtained.
1. In erythrocytes from untreated patients with diabetic ketoacidosis, the cellular levels of fructose-6-phosphate were significantly increased (P<0.05) and those of fructose-1, 6-bisphosphate, glyceraldehyde-3-phosphate plus dihydroxyacetone phosphate, 2, 3-DPG and 3-phosphoglycerate were significantly decreased (P<0.05, 0.05, 0.001 and 0.01, respectively). The crossover point was shown to be at thephosphofructokinase (PFK) step.
2. This glycolytic pattern in erythrocytes was similar to that of a patient with hereditary partial deficiency of erythrocyte PFK, strongly suggesting that the fall in 2, 3-DPG level in diabetic ketoacidosis is due to inhibition of PFK activity.
3. Normal human erythrocytes were incubated in the presence of β-hydroxybutyrate, acetoacetate, palmitate or insulin or at various pH levels in the absence of these substances. Glycolytic flow and intracellular glycolytic intermediates were not affected by ketone bodies, palmitate or insulin. Marked decreases in glycolytic intermediates below the PFK step and increases in intermediates above the PFK step associated with a significant reduction in glycolytic flow, were observed only at low pH levels.
4. It was also demonstrated in experiments using partially purified enzyme preparations that the PFK activity was dependent on pH and not affected by ketone bodies.
It is concluded that the fall in 2, 3-DPG level in diabetic ketoacidosis is caused by inhibition of PFK activity, and that this inhibition is due maily to an increase in hydrogen ion concentration and not to changes in the β-hydroxybutyrate, acetoacetate, insulin or palmitate concentration in the blood.
