[Formation and action of epimerase from Azotobacter vinelandii]

After exhaustion of the C-source, terminating the accumulation of the extracellular polysaccharide, the excretion of the epimerase is increased, accordingly the moiety of guluronosyls of the alginate is augmented. Epimerization reactions with an epimerase preparation with commercial alginates from algae lead to higher conversion rates than with alginate from Azotobacter vinelandii. It is reasoned that the acetyl groups of bacterial alginate perform a steric hinderance. Because of the small amount of guluronosyls in Azotobacter alginate, these alginates do not form gels with Ca++.