 Each pair has a conventional name (like "glucose" or "fructose"), and the two members are labeled "-" or "-", depending on whether the hydroxyl in position 5, in the Fischer projection of the molecule, is to the right or to the left of the axis, respectively.These labels are independent of the optical activity of the isomers.In general, only one of the two enantiomers occurs naturally (for example, -glucose) and can be metabolized by animals or fermented by yeasts.