PARTIAL-PURIFICATION OF AMYLASES AND STARCH PHOSPHORYLASES FROM POPLAR WOOD

The three main fractions of amylase activity and both starch phosphory lase isoforms from xylem parenchyma cells of poplar twigs (Populus x c anadensis Moench <<robusta>>) were separated by Q Sepharose anion exch ange chromatography and gel filtration through Sephacryl S-300-HR. Ana lysis of the substrate specificity of the starch hydrolases showed tha t the chromogenic substrates, blocked PNP-linked G5 and G6 maltooligos accharides (Testomar) and starch azure, were highly specific for assay ing beta-amylase (EC 3.2.1.2) and a-amylase (EC 3.2.1.1) activity, res pectively. In this way, five bands of the complex electrophoretic amyl ase isozyme pattern in protein extracts from poplar wood were identifi ed as alpha-amylases (A1-A5), and three bands (B1-B3) as beta-amylases . Product analysis by HPLC supported these results. Exoamylase release d almost exclusively maltose from soluble starch, while several maltoo ligosaccharides, G6-G10 being the main products, were released by alph a-amylase. Another amylase band of unknown classification was able to degrade starch granules and polysaccharides immobilized in acrylamide gels, but was inactive with soluble polysaccharide substrates. Poplar wood extracts contained two bands of starch phosphorylase (EC 2.4.1.1) activity, which exerted typical properties of the Type I (cytoplasmic ) and Type II (plastidic) isoforms.