Carbohydrate composition and electrophoretic properties of tomato polygalacturonase isoenzymes

Abstract

Two polygalacturonase isoenzymes, PG I and PG II, were extracted from Murrieta tomato and purified by gel exclusion and ion‐exchange chromatography. The kinetic constants and activation energies of the purified isoenzymes have been determined. Polygalacturonase I has two polypeptide chains (M_r= 47500 and 41400) whereas polygalacturonase II is a single polypeptide (M_r= 47500) as shown by electrophoresis in polyacrylamide gels in the presence of sodium dodecyl sulphate. Both isoenzymes are glycoproteins. Through gas liquid chromatography, polygalacturonase II was shown to contain 4.6% neutral hexoses and 1.5% amino sugars. There are eight d‐mannose, two l‐fucose, two d‐xylose and three N‐acetylglucosamine residues per mole of PG II. The carbohydrate portion of PG II was shown to be attached to the protein part through an N‐acetylglucosaminylasparaginyl bond.