Conversion of galactose and glucose to liver glycogen in vivo.

Topper and Stetten (1) fed n-galactose-l-Cl4 by stomach tube to fasted rats and isolated glucose from the liver glycogen. About 90 per cent of the Cl4 was in C-l of the glucose unit of glycogen. They concluded that a direct epimerization of carbon 4 of the n-galactose occurred rather than a rupture of the carbon skeleton (1). However, any mechanism which removed C-l and which formed glycogen from all or part of the remaining 5 carbon atoms would not be detected with galactose-l-C14. Thus the 6-phosphogluconate oxidative pathway might give rise to unlabeled hexose and only the direct conversion of galactose to glucose would be evident with galactose-l-CY4. It has been observed by Krebs (2) and others1 that under anaerobic conditions Escherichia coli produces much larger amounts of succinate from galactose than from glucose. Also, Pierce and White (3, 4) have reported that Streptococcus pyogenes formed 1 mole of lactic acid per mole of galactose, in contrast to glucose from which 2 moles of lactic acid were formed per mole. These observations suggest that there are differences in the metabolism of the carbon chain of galactose and glucose. The purpose of the present investigation was to compare the isotope distribution in the liver glycogen produced from n-galactose-2-Cl4 with that produced from n-glucose-2-Cr4. If n-galactose-2-C14 were metabolized in the same way as the n-glucose-2C14, then the isotope distribution in the liver glycogen should be the same in both cases. Any significant deviation in the isotope distribution in the liver glycogen might indicate either that the hexoses are metabolized via different pathways or that one hexose is metabolized by one pathway to a greater extent than the other hexose. Further information concerning the conversion of galactose to glycogen was obtained with the use of randomly labeled