This family contains L-rhamnose mutarotase which is a glycosyl hydrolase that converts the monosaccharide L-rhamnopyranose from the alpha to the beta stereoisomer. In Escherichia coli this enzyme is the product of the rhaM gene (also known as yiiL). The tertiary structure has been solved, in complex with L-rhamnose, and the catalytic mechanism determined. His22 is the proton donor. The enzyme naturally exists as a dimer.