[Polysaccharides enzymatic degradation in heterogeneous phase: example of agarases and carrageenases].

Agars and carrageenans are sulphated galactans which assemble in the red algal cell wall as a dense network of semi-crystalline fibers. These polysaccharides are degraded in heterogeneous phase by bacterial enzymes, namely agarases and carageenases. Crystallographic as well as enzymologic investigations of the sulphated galactans/galactanases systems highlight that the properties of these catalysts are well adapted to the degradation of solid polyanionic substrates. Indeed, as for cellulases or amylases, they are able to depolymerize their respective substrates according to a processive mode of action. However, at the molecular level, they are distinguished by the ionic nature of the interactions involved which do not allow the direct transposition of the processivity models developed for the degradation of neutral polysaccharides.