A white-rot fungus Dichomitus squalens, when grown on 1% wheat-straw glucuronoarabinoxylan under aerated submerged conditions, secreted an a-~arabinofuranosidase (4.3 nkat/mL). The enzyme was purified 70-fold by ammonium sulfate precipitation, chromatofocusing on PBE 94, gel filtration on Ultrogel AcA 54, rechromatofocusing on PBE 94, and lectin affinity chromatography on Concanavalin A-Ultrogel. The enzyme is a glycoprotein having a molecular weight of 60,000 and a p1 of 5.1. The enzyme exhibited maximal activity at pH 3.5 and at 60", and was fully inactivated within 30 min at 70". The K,,, value for p-nitrophenyl a-L-arabinofuranoside was 1.64mM. The a-L-arabinofuranosidase liberated arabinose from sugar-beet arabinan, wheat-straw and oat-spelt arabinoxylans, and wheat-bran heteroxylan, and was inactive towards gum arabic.
INTRODUmION
Plant arabinose-containing polysaccharides are arabinoxylans, neutral pectic substances (namely, type I arabinogalactans and arabinans), and type II arabinogalactans' (including exudate gums). Arabinose, generally in the a+furanose form, constitutes monomeric and/or oligomeric side-chains in arabinoxylans and both types of arabinogalactans, and the core of (1+5)-a-arabinans. Arabinose has also been said to play a role in the lignin-xylan covalent interaction2y3.
Enzymes which cleave a-L-arabinofuranosidic linkages occurring in these polymers are arabinosidases4g5: a-r_-arabinofuranosidases (EC 3.2.1.55), endo-(l--+5)-cu+arabinanases (EC 3.2.1.99), and a new type of exo-(1+5)-a-L-arabinanase4. We have obtained6 an endo-(1-4)~P-o-xylanase from Irpex lucteus, which is *To whom correspondence should be addressed.