Studies on the Pectic Substances of Plant Cell Walls

Abstract

Pectate lyase was isolated from the cell extract of E. aroideae. The enzyme was purified to a high degree by a procedure involving ammonium sulfate fractionation and chromatography on CM-Sephadex C-50 and on Sephadex G-200. The enzyme attacked its substrate in an endo fashion and was more active on the Na salt of acid-insoluble polygalacturonate or pectic acid than it was on the methoxylated pectin. The enzyme had an optimum pH at 9.3, was stimulated by Ca2+ and was completely inhibited by EDTA. The reaction products had an absorption maximum between 230 and 235 nm and reacted with thiobarbituric acid. Evidently, the purified enzyme is an endopectate lyase. The endopectate lyase solubilized effectively the pectic fraction from the cell walls of carrot (D. carota) root tissue. The enzyme released 30.5% of the wall as soluble products and liberated all of the galacturonic acid present in the walls. The total neutral sugars released by the enzyme were 10.6% of the walls, which corresponded to 71.5% of noncellulosic neutral sugars. The soluble products were separated into 5 fractions by DEAE-Sephadex A-50 column chromatography. Based on the analysis of sugar composition of each fraction, the pectic fraction of carrot cell wall is presented.