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It is claimed that bifidobacteria have several health-promoting effects. To increase the amount of bifidobacteria in the colon the concept of probiotics and/or prebiotics can be applied. Bifidobacterium adolescentis is one of the main species of bifidobacteria in the gastro-intestinal tract of human adults. B. adolescentis is able to degrade a wide range of oligosaccharides and a number of glycosyl hydrolases have been characterized in detail. The hydrolytic activity of the glycosyl hydrolases from B. adolescentis toward prebiotics like arabinoxylan-oligosaccharides, isomalto-oligosaccharides, arabinogalactan, and sucrose-based oligosaccharides (raffinose, stachyose, and fructo-oligosaccharides) is reviewed. Alternatively, some of these glycosyl hydrolases are able to catalyze transglycosylation, which allows them to elongate oligosaccharides and to prepare potentially prebiotic oligosaccharides. Such oligosaccharides might be used to influence the microbial composition in the more distal parts of the colon. In nature, not all enzyme-substrate encounters are transglycosylating. So, the hydrolytic activity of the enzyme makes the oligosaccharide elongation less efficient than desired. Site-directed mutagenesis was applied to improve the transglycosylation reaction of the $\alpha$-galactosidase from B. adolescentis., Les glycosyl hydrolases de Bifidobacterium adolescentis DSM20083. Il est affirmé que les bifidobactéries ont des propriétés bénéfiques sur la santé. Pour augmenter la teneur en bifidobactéries au niveau du colon, le concept de probiotiques et/ou prébiotiques peut être appliqué. Bifidobacterium adolescentis est l'une des principales espèces de bifidobactéries dans le tractus gastro-intestinal des adultes. Certaines des glycosyl hydrolases de B. adolescentis ont été caractérisées en détail et elles semblent dégrader un large éventail d'oligosaccharides. L'activité d'hydrolyse des glycosyl hydrolases de B. adolescentis envers des prébiotiques tels que les arabino-xylanes, isomalto-oligosaccharides, arabino-galactanes et les oligosaccharides contenant du saccharose (raffinose, stachyose et fructo-oligosaccharides) est passée en revue. De plus, certaines de ces glycosyl hydrolases peuvent être utilisées pour préparer des oligosaccharides prébiotiques potentiels par transglycosylation, ce qui permet d'allonger les oligosaccharides. De tels oligosaccharides peuvent être utilisés pour influencer la composition microbienne au niveau des parties plus distales du colon. Les produits de rencontre enzymes-substrates ne sont pas tous transglycosylés naturellement et l'activité d'hydrolyse de l'enzyme entraîne une élongation de l'oligosaccharide moindre que celle désirée. La mutagenèse dirigée a été appliquée pour améliorer la réaction de transglycosylation de l'$\alpha$-galactosidase de B. adolescentis.

The four major oligomeric reaction products from saponified modified hairy regions (MHR-S) from apple, produced by recombinant rhamnogalacturonan (RG) alpha-L-rhamnopyranosyl-(1, 4)-alpha-D-galactopyranosyluronide lyase (rRG-lyase) from Aspergillus aculeatus, were isolated and characterized by 1H-nuclear magnetic resonance spectroscopy. They contain an alternating RG backbone with a degree of polymerization of 4, 6, 8, and 10 and with an alpha-Delta-(4,5)-unsaturated D-galactopyranosyluronic acid at the nonreducing end and an L-rhamnopyranose at the reducing end. L-Rhamnopyranose units are substituted at C-4 with beta-galactose. The maximum reaction rate of rRG-lyase toward MHR-S at pH 6.0 and 31 degreesC was 28 units mg-1. rRG-lyase and RG-hydrolase cleave the same alternating RG I subunit in MHR. Both of these enzymes fragment MHR by a multiple attack mechanism. The catalytic efficiency of rRG-lyase for MHR increases with decreasing degree of acetylation. Removal of arabinose side chains improves the action of rRG-lyase toward MHR-S. In contrast, removal of galactose side chains decreased the catalytic efficiency of rRG-lyase. Native RG-lyase was purified from A. aculeatus, characterized, and found to be similar to the rRG-lyase expressed in Aspergillus oryzae.

A new enzyme, rhamnogalacturonan (RG) alpha-d-galactopyranosyluronohydrolase (RG-galacturonohydrolase), able to release a galacturonic acid residue from the nonreducing end of RG chains but not from homogalacturonan, was purified from an Aspergillus aculeatus enzyme preparation. RG-galacturonohydrolase acted with inversion of anomeric configuration, initially releasing beta-d-galactopyranosyluronic acid. The enzyme cleaved smaller RG substrates with the highest catalytic efficiency. A Michaelis constant of 85mgr;m and a maximum reaction rate of 160 units mg-1 was found toward a linear RG fragment with a degree of polymerization of 6. RG-galacturonohydrolase had a molecular mass of 66 kD, an isoelectric point of 5.12, a pH optimum of 4.0, and a temperature optimum of 50 degreesC. The enzyme was most stable between pH 3.0 and 6.0 (for 24 h at 40 degreesC) and up to 60 degreesC (for 3 h).