L-Xylose (L-(-)-Xylose), a levo-isomer of Xylose, is classified as an aldopentose-type monosaccharide.

The permeability characteristics of L-xylose have been compared in isolated intact rat diaphragm muscle preparations, in the absence and presence of exogenous insulin. In the absence of added insulin, L-xylose distributed in less than a third of the total cell water. In the presence of added insulin, intracellular distribution of L-xylose is increased. L-Xylose distributed in 50 per cent of the intracellular water. A significant lag period was observed before the insulin effect upon the penetration of L-xylose was evident. The lag period with L-xylose could be abolished by pretreating the tissues with insulin for 1 hour[2].