Cell wall localization of the natural substrate of a β‐galactosidase, the main enzyme responsible for the autolytic process of Cicer arietinum epicotyl cell walls

Abstract

The Hw pectic fraction, extracted with hot water, is the major componen! of 4 days old epicotyl cell walls of Cicer arietinum L. cv. Castellana and is formed of arabinose and galactose, with smaller amounts of rhamnose, xylose, glucose and mannose. The cell wall 2betaIII enzymatic fraction, with beta-galactosidase activity (EC 3.2.1.23) and the main enzyme responsible for the autolytic process. essentially acts on the Hw frac­tion, and is able to hydrolyze 560 µg of this fraction per g of epicotyls, releasing mainly galactose as monosaccharide. The 2betaIII fraction acts very weakly on the other polysaccharide fractions of the cell wall, both pectic and hemicellulosic, releasing 80, 60 and 14 µg per g of epicotyls from the fractions extracted with oxalate (Ox), KOH 10% (KI) and KOH 24% (KII), respectively. It can be concluded that the natural substrate of this enzyme is the Hw pectic fraction, probably an arabinogalactan that is found in the cell wall in isolated form or as side chains of the rhamnogalacturonan l.