D-Mannose-6-phosphate (M6P) is a phosphorylated aldohexose that has diverse physiological roles. It can be used to produce glucose as an energy source, converted to mannitol to serve as an osmolyte or metabolic store, or directed to the N-glycosylation pathway. M6P is also a ligand for both cation-dependent and -independent receptors and binds, as part of an N-glycan, to mannose receptor homology domains on other proteins.