Abstract
The molecular weight of polymeric alginic acid digested by alginate lyase (poly(1,4-β- d-mannuronide) lyase, EC 4.2.2.3) was determined at various stages of the lysis. Low molecular weight fragments were detected only after 60–100% lysis. Some high molecular weight fragments remained intact even after addition of a fresh aliquot of enzyme to the digest. The enzyme showed maximal activity at pH 5.6 in 0.05 M salt. Enzyme activity was stimulated by addition of 7.5 mM CalCl 2 and 0.2 M NaCl, when the pH optimum was between 8 and 8.5. Only mannuronic acid was detected at the reducing end of fragments after exhaustive enzymolysis, reduction and hydrolysis. On studying the reaction products by NMR, a double-bond signal ( σ= 5.98 ppm _ was observed. A considerable decrease in intensity of the d-mannuronic acid residue signal was detected after hydrolysis of alginate lyase VI on poly-(ManUA-GulUA), but not poly(GulUA). The results suggest that alginate lyase VI may be an endoalginate lyase that splits glycoside bonds only between two mannuronic acid residues.
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