Oxidation of galactose by galactose-1-phosphate uridyltransferase-deficient lymphoblasts

The ability of EB virus-transformed lymphoblasts with undetectable galactos e-1-phosphate uridyltransferase (GALT) from 15 galactosaemic patients to ox idize [1-C-14]galactose to (CO2)-C-14 was compared to that of cells from 7 normal subjects. The oxidation of galactose but not of glucose was markedly diminished by cells from Q188R homozygous galactosaemic patients but was n ot absent. After 2.5 h these cells liberated (CO2)-C-14 at nearly 3% and at 5 h up to 9% of normal. Cells from patients homozygous for the S135L mutat ion produced much larger amounts of (CO2)-C-14 (15-17% of normal) and were distinguishable from the Q188R homozygous cells. A cell line with a homozyg ous deletion of the GALT gene oxidized galactose at 7% of the normal rate, suggesting that pathways(s) other than GALT exist in these cells as well as Q188R homozygous cells for oxidation of galactose to CO2. Concentration de pendence studies are consistent with the presence of a pathway that is unsa turable or has a very high K-m. The ability of 10(7) lymphoblasts with the S135L genotype to oxidize more than 7% of the sugar to (CO2)-C-14 in 5 h su ggests the presence of residual GALT despite the inability to detect the ac tivity by enzymatic analysis.