Screening for erros in galactose metabolism with the erythrocyte

We propose determination of the ratio of the rate of galactose metabolism to glucose metabolism by erythrocytes as a screening test for abnormalities in glucose and galactose metabolism. Packed erythrocytes (20 mul) are incubated for 1 h at 37 degrees C in 0.42 ml of a solution comprising phosphate buffer (pH 7.4), 0.4 mg of glucose, 60 mg of methylene blue, and 50 nCi of either [1-14C]glucose or [1-14C]galactose. Metabolism is then stopped by injecting dilute H2SO4 through a rubber septum sealing the flasks. On incubating the acidified solution for 1 h, the evolved CO2 is trapped in a well containing ethanolamine, which is suspended from the septum. The radioactivity of the well and its contents is measured in a scintillator, and from these data CO2 is calculated. (The scintillation medium is preheated with ethanolamine to eliminate chemiluminescence.) For normal adults mean values for CO2 are 0.468 mumol/liter of erythrocytes per minute for galactose and 37.8 mumol/liter of erythrocytes per minute for glucose. Homozygous galactosemics exhibit no galactose metabolism but the rate for flucose metabolism is normal. Results for parents of homozymotes are described. We review various causes for galactosemia and point out that transfer of galactose through the cell wall and into the erythrocyte is markedly reduced in certain cats and, although unreported, may possibly be a cause for galactosemia in humans.