Galactose-1-phosphate uridyltransferase activities in erythrocytes from a patient with galactosemia: discrepancy between two methods.

When measuring with the spectrophotometric UDP-Glu consumption test, the galactose-1-phosphate uridyltransferase (Gal-PUT) activity in erythrocyte lysates from a 22-month-old infant with a late onset form of galactosemia was found to be approximately 25% of normal. With a radiochemical assay only a very low residual activity could be detected (+/- 1% of normal). Preincubation of the patient's lysate with purified NADase caused a marked decrease of residual Gal-PUT activity as judged from the data obtained with the consumption test. The radiochemical assay was not influenced by a similar pre-treatment. The high level of residual activity found with the consumption test in this patient was attributed to the consumption of UDP-Glu by other reactions than Gal-PUT. Because it is a direct, simple and generally applicable assay, the radiochemical procedure is suggested to be the best method for the more detailed enzymological characterisation of the Gal-PUT deficient state in galactosemics.