Characterization, Hydrolytic Activity and Variations throughout Growth of a Cell Wall β-Glucosidase and a-Galactosidase from Cicer arietinum epicotyls

Abstract

In the cell walls of epicotyls of Cicer arietinum we found beta-glucosidase and a-galactosidase activities, the former being predominant. We purified and characterized these enzymatic activities. The beta-glucosidase activity is found associated with a protein fraction that also shows beta-galactosidase and beta-xylosidase activ­ity. lt is formed by two subunits of approximately 60-65 kDa, with elevated activity between pH 6 and 8 and an optima! temperature of 70 ºC, inhibited by Hg2+ . The values of Km and Vmax vary for each of its principal activities, being 2.2 mM and 378.6 nkat (mg protein)- 1, respectively, for beta-glucosidase activity. The fraction with the a-galactosidase activity is also formed by subunits of molecular weight of 35-45 kDa. lt shows an optimum pH of 5 and 40 ºC, its Km and V max being 0.27 mM and 32.8 nkat (mg protein)- 1. lt is inhibited by Hg2+ and galactose. Throughout growth of the epicotyls, beta-glucosidase ac­tivity increased and a-galactosidase showed an activity profile with a maximum to the 5th day. These en­zymes were not able to hydrolyze the non-cellulosic fractions of the cell wall. lts physiological role re­mains unknown.