Characterization of exo-(1,4)-alpha glucan lyase from red alga Gracilaria chorda. Activation, inactivation and the kinetic properties of the enzyme

Exe-(1,4)-alpha glucan lyase (GLase) was purified from a red alga Gracilari a chorda. The enzyme was activated 1.3-fold in the presence of Ca2+ and Cl- ions. The ions also stabilized the enzyme increasing the temperature of it s maximum activity from 35 degrees C to 50 degrees C. GLase was inactivated by chemical modification with carbodiimide and a carboxyl group of the enz yme was shown essential to the lyase activity. A tryptophanyl residue(s) wa s also shown to be important for the activity and was probably involved in substrate binding. K-m values of the enzyme were 2.3 mM for maltose, 0.4 mM for maltotriose and 0.1 mM for maltooligosaccharides of degree of polymeri zation (dp) 4-7. and the k(0) values for the oligosaccharides were similar (42-53 s(-1)). The analysis of these kinetic parameters showed that the enz yme has four subsites to accommodate oligosaccharides. The subsite map of G Lase was unique, since subsite I and subsite 2 have large positive and smal l negative affinities, respectively. The subsite map of this type has not b een found in other enzymes with exo-action on alpha-1,4-glucan. The K-m and k(0) values for the polysaccharides were lower (0.03 mM) and higher (60-10 0 s(-1)), respectively, suggesting the presence of another affinity site sp ecific to the polysaccharides. (C) 1999 Elsevier Science B.V. All rights re served.