Transport and metabolism of galactose in rat kidney cortex

Abstract

1. Analysis of transport of d-galactose was complicated by metabolism of the compound but appeared to have two components: a substrate-saturable component and a diffusion component. At low substrate concentration (<1mm) active transport was observed. Accumulation of galactose was largely independent of Na+concentration. The apparent Km for this component was 0.2mm. At substrate concentrations above 1mm the active transport system appeared saturated and further increases in substrate concentration resulted in a linear increase in the rate of galactose accumulation, but no concentration gradient was formed. 2. d-[1-14C]Galactose (2mm) was metabolized to14CO2 by rat kidney-cortex slices incubated at 37°C, at the rate of 68nmol/h per 100mg of tissue. 3. Intracellular components from such incubations were separated into a neutral fraction, the only major labelled component being galactose, and a phosphorylated fraction. 4. Phosphorylated metabolites found in galactose-incubated slices increased with increasing substrate concentration and achieved a limiting value of 0.42mm after 60min of incubation. 5. Galactose uptake was inhibited by anaerobiosis, dinitrophenol and phlorrhizin. 6. Methyl α-d-glucoside and d-glucose partially inhibited galactose uptake only at ratios of 100:1. 7. The presence of pyruvate did not decrease galactose metabolism although it did decrease production of14CO2 from [1-14C]galactose. Gluconeogenesis occurred in the presence of pyruvate and14C from galactose was found in glucose. 8. Rat kidney-cortex slices metabolized 2mm-[1-14C]galactonate to14CO2 at a rate of 20nmol/h per 100mg of tissue.