Heparan sulfates and heparins: similar compounds performing the same functions in vertebrates and invertebrates?

The distribution and structure of heparan sulfate and heparin are briefly r eviewed. Heparan sulfate is a ubiquitous compound of animal cells whose str ucture has been maintained throughout evolution, showing an enormous variab ility regarding the relative amounts of its disaccharide units. Heparin, on the other hand, is present only in a few tissues and species of the animal kingdom and in the form of granules inside organelles in the cytoplasm of special cells. Thus, the distribution as well as the main structural featur es of the molecule, including its main disaccharide unit, have been maintai ned through evolution. These and other studies led to the proposal that hep aran sulfate may be involved in the cell-cell recognition phenomena and con trol of cell growth, whereas heparin may be involved in defense mechanisms against bacteria and other foreign materials. All indications obtained thus far suggest that these molecules perform the same functions in vertebrates and invertebrates.