Enzymatic degradation of cross-linked dextrans

The enzymatic degradation of intramolecularly polymerized methacrylated dextran [dex-poly(MA)] and hydrogels based on methacrylated dextran was studied. Dex-poly(MA) was synthesized as a soluble model compound to investigate the enzymatic degradation of dextran hydrogels. After degradation of hydrogels and dex-poly(MA) by dextranase, the formed products were analyzed by gel permeation chromatography (GPC) and electrospray mass spectrometry (ES-MS). GPC analysis revealed that besides low-molecular-weight fractions (180-1100 Da) a soluble high-molecular-weight fraction (9-94 kDa) also was formed for both dextran hydrogels and dex-poly(MA). The high-molecular-weight products in degraded dextran hydrogels and dex-poly(MA) increased both in relative amount and in molecular weight with increasing degree of methacrylate substitution. This fraction most likely consisted of oligosaccharides bound to polymerized methacrylate groups. ES-MS showed that the low-molecular-weight fractions consisted of glucose, isomaltose and some larger unsubstituted oligosaccharides. The same products were formed after enzymatic degradation of native dextran. The enzymatic degradation of dex-poly(MA) as well as dextran hydrogels was described with kinetic models. Combination of enzyme kinetics, GPC and ES-MS lead to the conclusion that the enzymatic degradation can be divided in two processes. First, long unsubstituted chains with a length of probably about 18 or more glucopyranose residues are hydrolyzed at a similar rate and extent as native dextran. Second, the enzyme binds to unsubstituted chain segments of 6 to about 18 glucopyranose residues, which are hydrolyzed slower. Shorter unsubstituted chain segments are not enzymatically degraded.