Campylobacter jejuni encodes numerous sugar-nucleotide-modifying enzymes potentially involved in the biosynthesis of surface carbohydrates. One of them, CJ1293, is involved in flagellin glycosylation but its biochemical activity remains unknown. Using over-expressed and purified protein, we demonstrate that CJ1293 has UDP-GlcNAc-specific C(6) dehydratase activity. Catalysis occurs without addition of cofactor, suggesting internal recycling of NAD(P)(+). The K(m) for UDP-GlcNAc of 50 microM indicates that CJ1293 has higher affinity for its substrate than previously characterized homologues. Based on enzymatic data, we propose that CJ1293 catalyzes the first step in the biosynthesis of bacillosamine, a sugar found in C. jejuni's protein glycosylation motifs.