RHAMNOGALACTURONAN ALPHA-D-GALACTOPYRANOSYLURONOHYDROLASE - AN ENZYMETHAT SPECIFICALLY REMOVES THE TERMINAL NONREDUCING GALACTURONOSYL RESIDUE IN RHAMNOGALACTURONAN REGIONS OF PECTIN

A new enzyme, rhamnogalacturonan (RG) alpha-D-galactopyranosyluronohyd rolase (RG-galacturonohydrolase), able to release a galacturonic acid residue from the nonreducing end of RG chains but not from homogalactu ronan, was purified from an Aspergillus aculeatus enzyme preparation. RG-galacturonohydrolase acted with inversion of anomeric configuration , initially releasing beta-D-galactopyranosyluronic acid. The enzyme c leaved smaller RG substrates with the highest catalytic efficiency. A Michaelis constant of 85 mu M and a maximum reaction rate of 160 units mg(-1) was found toward a linear RG fragment with a degree of polymer ization of 6. RG-galacturonohydrolase had a molecular mass of 66 kD, a n isoelectric point of 5.12, a pH optimum of 4.0, and a temperature op timum of 50 degrees C. The enzyme was most stable between pH 3.0 and 6 .0 (for 24 h at 40 degrees C) and up to 60 degrees C (for 3 h).