In enzymology, a chitobiosyldiphosphodolichol beta-mannosyltransferase (EC 2.4.1.142) is an enzyme that catalyzes the chemical reaction

GDP-mannose + chitobiosyldiphosphodolichol GDP + beta-1,4-D-mannosylchitobiosyldiphosphodolichol

Thus, the two substrates of this enzyme are GDP-mannose and chitobiosyldiphosphodolichol, whereas its two products are GDP and beta-1,4-D-mannosylchitobiosyldiphosphodolichol.

This enzyme belongs to the family of glycosyltransferases, specifically the hexosyltransferases. The systematic name of this enzyme class is GDP-mannose:chitobiosyldiphosphodolichol beta-D-mannosyltransferase. Other names in common use include guanosine diphosphomannose-dolichol diphosphochitobiose, mannosyltransferase, and GDP-mannose-dolichol diphosphochitobiose mannosyltransferase. This enzyme participates in n-glycan biosynthesis and glycan structures - biosynthesis 1.

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• Takahashi T, Honda R, Nishikawa Y (2000). "Cloning of the human cDNA which can complement the defect of the yeast mannosyltransferase I-deficient mutant alg 1". Glycobiology. 10 (3): 321–7. doi:10.1093/glycob/10.3.321. PMID 10704531.