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Biosynthesis of T1 Antigen in Salmonella: Origin of D-Galactofuranose and D-Ribofuranose Residues

^a Department of Bacteriology and Immunology, University of California, Berkeley, California 94720

ABSTRACT

The "T1 side chain" portion of cell wall lipopolysaccharide from T1 strains of Salmonella contains D-galactofuranose and D-ribofuranose residues. Isotope labeling studies, using intact cells of mutants each blocked at either of the two different steps of D-galactose metabolism (uridine diphosphate-glucose 4-epimerase and galactose-1-P uridylyl transferase) or at phosphoglucoisomerase, led to the following conclusions. (i) D-Galactofuranose residues are synthesized from D-galactopyranose or its derivatives, rather than by a direct conversion from other hexopyranoses or their derivatives. (ii) The pyranose-to-furanose conversion does not appear to take place at the level of the free D-galactose or D-galactose 1-phosphate. This result suggests that the conversion may occur at the stage of uridine diphosphate-D-galactose. (iii) In a mutant lacking phosphoglucoisomerase, D-ribofuranose residues in T1 side chains contained ¹⁴C derived from exogenous D-fructose-U-¹⁴C, but little ³H from exogenous D-glucose-1-³H. Thus, no evidence was found for a direct pathway of aldohexose-to-ribose conversion involving a loss of one of the carbons in the C2-C6 moiety of aldohexoses. This suggests, but does not prove, that the T1 ribofuranose residues are synthesized by conventional mechanisms involving hexose monophosphate shunt and transketolase-transaldolase reactions.

¹ Present address: Central Public Health Laboratory, Mannerheimintie 166, Helsinki 28, Finland.

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