Biological Mechanisms Involved in the Formation of Deoxysugars

The biosynthesis of thymidine diphospho-l-rhamnose from thymidine diphosphoglucose specifically labeled with tritium at carbon 3 has been studied with an enzyme preparation from Escherichia coli B. Under conditions in which conversion to the 6-deoxysugar was essentially quantitative, 10% of the initial radioactivity was recovered in the rhamnose; the remainder of the tritium was located in thymidine diphospho-4-keto-6-deoxyglucose. Degradation of the enzymatically synthesized l-rhamnose established the following tritium distribution: carbon 6, 55%; carbon 2, 44%; carbon 3, 1%; and carbon atoms 1, 4, and 5, less than 0.5%. The interpretation of these results is discussed in terms of the mechanisms operative during the biosynthesis of l-rhamnose.