Purification, characterization, and cell wall localization of an α‐fucosidase that inactivates a xyloglucan oligosaccharin

Summary An α‐fucosidase that releases fucosyl residues from oligosaccharide fragments of xyloglucan, a plant cell wall hemicellulosic polysaccharide, was purified to homogeneity from pea ( Pisum sativum ) epicotyls using a combination of cation exchange chromatography and isoelectric focusing. The α‐fucosidase has a molecular mass of 20 kDa according to sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. The α‐fucosidase has an isoelectric point of 5.5. The substrate specificity of the α‐fucosidase was determined by high performance anion exchange chromatographic analysis of oligosaccharide substrates and products. The enzyme hydrolyzes the terminal α‐1,2‐fucosidic linkage of oligosaccharides and does not cleave p ‐nitrophenyl‐α‐L‐fucoside. The enzyme does not release measurable amounts of fucosyl residues from large polysaccharides. The subcellular localization of α‐fucosidase in pea stems and leaves has been studied by immunogold cytochemistry. The α‐fucosidase accumulates in primary cell walls and is not detectable in the middle lamella or in the cytoplasm of 8‐day‐old stem tissue and 14‐day‐old leaf tissue. α‐Fucosidase activity was readily detected in extracts of 8‐day‐old stem tissue. No significant α‐fucosidase acitivity or immunogold labeling of the α‐fucosidase was detected in 2‐ and 4‐day‐old stem tissue indicating that production of α‐fucosidase is developmentally regulated.