ALPHA-(4-O-METHYL)-D-GLUCURONIDASE ACTIVITY PRODUCED BY THE RUMEN ANAEROBIC FUNGUS PIROMONAS-COMMUNIS - A STUDY OF SELECTED PROPERTIES

The rumen anaerobic fungus Piromonas communis, unlike the rumen anaero bic fungi Neocallimastix frontalis and Neocallimastix patriciarum, pro duced extracellular alpha-(4-O-methyl)-D-glucuronidase when grown in c ultures containing filter-paper, barley straw, birchwood xylan or birc hwood sawdust as carbon source. The highest concentration of enzyme wa s produced in cultures containing birchwood sawdust. The aldobiouronic acid O-alpha-(4-O-methyl-D-glucopyranosyluronic acid)-(1 --> 2)-D-xyl opyranose (MeGlcAXyl) was the best substrate of those tested: the aldo triouronic acid O-alpha-(4-O-methyl-D-glucopyranosyluronic acid (1 --> 2)-O-beta-D-xylopyranosyl-(1 --> 4)-D-xylopyranose (MeGlcAXyl(2)) and the aldotetraouronic acid O-alpha-(4-O-methyl-D-glucopyranosyluronic acid)-(1 --> 2)-O-beta-D-xylopyranosyl-(1 --> 4)-O-beta-D-xylopyranosy l-(1 --> 4)-D-xylopyranose (MeGlcAXyl(3)) were also attacked but the r ate fell as the degree of polymerisation increased. When the same subs tituted xylooligosaccharides were reduced to the corresponding alditol s the enzyme activity disappeared. Similarly, p-nitrophenyl-alpha-D-gl ucuronide was not a substrate. Remarkably, the relative rates of attac k shown by the alpha-(4-O-methyl)-D-glucuronidase on the aldouronic ac ids and on xylans extracted from birchwood, oat spelts and oat straw d iffered according to the carbon source used to produce the enzyme. The alpha-(4-O-methyl)-D-glucuronidase had a pH optimum of 5.5 and a temp erature optimum of 50 degrees C. On gel filtration the enzyme was show n to be associated with proteins covering the range 100-300 kDa, but a major peak of activity in the column effluent appeared to have a mole cular mass of 103 kDa.