Glucose and galactose dif- fer only in configuration around carbon 4, and so are C-4 epimers that are interconvertible by the action of an epimerase. Glucose is an aldose sugar that typically exists as a pyranose ring in solution; fructose, however, is a ketose with a furanose ring. The D-isomeric form of carbohy- drates is most typically the form found in biologic systems, in contrast to amino acids. Salivary amylase does not produce monosaccharides. Homopolysaccharides of glucose include branched glycogen in which the glycosidic link- ages are the α form, as well as unbranched cel- lulose that has β linkages