 The biosynthesis of colitose begins with ColE, a mannose-1-phosphate guanylyltransferase that catalyzes the addition of a GMP moiety to mannose, yielding GDP-mannose.In the next step, ColB, an NADP-dependent short-chain dehydrogenase-reductase enzyme, catalyzes the oxidation at C-4 and the removal of the hydroxyl group at C-6.The resulting product, GDP-4-keto-6-deoxymannose, then reacts with the PLP-dependent enzyme GDP-4-keto-6-deoxymannose-3-dehydratase (ColD), which removes the hydroxyl at C-3 in a manner similar to that of serine dehydratase.