COATING ALGINATE BEADS WITH CROSS-LINKED BIOPOLYMERS - A NOVEL METHODBASED ON A TRANSACYLATION REACTION

Stable membranes were formed around alginate beads using a transacylat ion reaction between polysaccharidic esters, namely propylene glycol a lginate (PGA) or pectin, and various proteins (human serum albumin (HS A), ovalbumin, bovine hemoglobin, lactoserum proteins). In a standard procedure, two reagents (PGA or pectin+protein) were added to a Na-alg inate solution: beads were formed by dropwise addition into a calcium solution. Then the transacylation reaction was started by alkalinizati on of the bead suspension. A membrane was formed around the beads, mad e of a protein directly bound to a polysaccharide through amide linkag es. The thickness of the membranes and the lysis time in trypsin were increased by raising the amount of NaOH used for the transacylation st ep. In a modified procedure, coated beads were obtained, incorporating PGA in the initial Na-alginate solution, and HSA in the transacylatio n bath. Activated charcoal was encapsulated in HSA-PGA beads, giving p articles with adsorption properties towards creatinine. Assays were pe rformed using PGA associated with alkaline phosphatase as the membrane -forming protein. Stable beads were obtained having a relative activit y of 39.3%, as compared with free enzyme.