Characterization of a cell wall β‐galactosidase of Cicer arietinum epicotyls involved in cell wall autolysis

Abstract

β‐Galactosidase (EC 3.2.1.23) has been established as the main enzyme involved in the autolytic process. The enzyme extracted from cell walls of epicotyls of Cicer arietinum L. cv. Castellana with 3 M LiCl is a 45 kDa protein composed of a single subunit, having an optimum pH of 4; an optimum temperature of 45°C and Km and Vmax of 1.72 mM and 18.5 nkat (mg protein)–1 respectively, as evaluated against p‐nitrophenyl‐β‐d‐galactopyranoside. The enzyme is inhibited by Hg2+, d‐galactono‐1,4‐lactone and galactose, substances that also inhibit the autolytic process. Ca2+ and EDTA, which do not affect the activity of the β‐gaiactosidase, do however modify the hydrolysis of the cell wall mediated by the enzyme, and they also inhibit the autolytic process. Ca2+ decreased both processes, whereas EDTA increased them; and when both substances were added together, their individual effects were neutralized. The effects of both agents is probably due to modifications in the cell wall that prevent access of the enzyme to its substrate.