A lactating mammary gland of a sheep and a goat were perfused for several hours in the presence of [U-14C]D-fructose and received adequate quantities of acetate, glucose and amino acids.
In both experiments, there was a small incorporation of 14C in the expired CO2. Smaller radioactivities were measured in milk citric acid, lactose, casein and fat, the activities decreasing in that order. The specific activities of the amino acids from one casein hydrolysate were determined. The highest radioactivities were found in alanine and serine; methionine, glutamic acid and aspartic acid showed a smaller incorporation of 14C.
These results indicate that fructose is metabolized only to a very limited extent by the mammary gland. The relative distribution of 14C observed among the different substances isolated may be explained by a direct splitting of fructose into two C3-fragments, glycolysis and metabolism via the Krebs cycle.