A new microfluorometric method for the measurement of galactose-1-phosphate in erythrocytes

A new and sensitive assay for measuring galactose-1-phosphate in erythrocytes is described. Galactose-1-phosphate is determined by mixing an aliquot of deproteinized hemolysate with a reagent containing uridine diphosphoglucose, NADP+, hexose-1-phosphate uridylyltransferase, phosphoglucomutase, glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase and measuring the NADPH formed fluorometrically. Under the conditions of this assay 2 mol of NADPH are formed per mol of galactose-1-phosphate. The assay is linear from 0 to 1160 micrograms of galactose-1-phosphate per gram of hemoglobin. Recovery of galactose-1-phosphate added to four hemolysates averaged 99%. Galactose-1-phosphate concentrations were measured in erythrocytes from five heterozygous subjects not under dietary control and seven transferase-deficient galactosemic individuals who were receiving galactose restricted diets. In all samples from the heterozygous individuals, the galactose-1-phosphate concentrations were normal. Of the samples from galactosemic subjects, two showed extreme elevations of galactose-1-phosphate, four showed moderate elevations, and one was normal. Galactose-1-phosphate levels are used to monitor the degree of dietary control in the transferase-deficient galactosemic individual.