Utilization of l-Ascorbate by Escherichia coli K-12: Assignments of Functions to Products of the yjf-sga and yia-sgb Operons

Escherichia coli K-12 can ferment l-ascorbate. The operon encoding catabolic enzymes in the utilization of l-ascorbate (ula) has been identified; this operon of previously unknown function had been designated the yif-sga operon. Three enzymes in the pathway that produce d-xylulose 5-phosphate have been functionally characterized: 3-keto-l-gulonate 6-phosphate decarboxylase (UlaD), l-xylulose 5-phosphate 3-epimerase (UlaE), and l-ribulose 5-phosphate 4-epimerase (UlaF). Several products of the yia-sgb operon were also functionally characterized, although the substrate and physiological function of the operon remain unknown: 2,3-diketo-l-gulonate reductase (YiaK), 3-keto-l-gulonate kinase (LyxK), 3-keto-l-gulonate 6-phosphate decarboxylase (SgbH), and l-ribulose 5-phosphate 4-epimerase (SgbE).