Dihydroxyacetone Metabolism by Human Erythrocytes: Demonstration of Triokinase Activity and Its Characterization

Dihydroxyacetone (DHA) was found rapidly to enter human erythrocytes. When incubated with intact red cells, ¹⁴C-labeled DHA rapidly appeared in intermediate metabolites and in lactate. Crude hemolysates were found to phosphorylate DHA and glyceraldehyde (GA) but not glycerol. Fifty-fold purification of the phosphorlylating enzyme was achieved by removal of hemoglobin on CM-52 and Sephadex G-200 chromatography. During purification there was no change in the ratio of DHA to GA utilization. The enzyme had a pH optimum of 6,6, a K_m of 0.5 µM for DHA, and a K_m of 11 µM for GA. With GA as substrate, the K_m for (ATP-MG)^2- complex was 1.45 mM, and no cooperative interaction was observed. With DHA as a substrate, cooperative interaction with respect to (ATP-Mg)^2- complex was found with an n value of 1.4 and a K of 0.44 mM. At temperatures between 15° and 40°C, the enzyme activity gave a linear Arrhenius plot, with deviation from linearity at lower temperature levels. The activity of the enzyme was 0.151 ± 0.011 U/g Hb in five normal subjects, and only slightly increased levels were observed in a patient with marked reticulocytosis. The DHA-phosphorylating activity of erythrocytes is attributed to the activity of triokinase (ATP: D-glyceraldehyde-3-phosphotransferase; E.C.2.7.1. 28). Although DHA is rapidly cleared from blood after injection into rabbits, substantial metabolism is possible for a prolonged time after administration because of the very low K_m of the enzyme for DHA. The capacity of red cells to utilize DHA may prove to be useful in the maintenance of 2,3-diphosphoglycerate (2,3-DPG) levels during blood storage and in the in vivo manipulation of red cell 2,3-DPG levels.