Intracellular alpha-L-rhamnosidase (EC 3.2.1.40) from the psychrotolerant Pseudoalteromonas sp. 005NJ showed a dose-dependent inhibition for L-rhamnose (IC(50) = 20 mM) and D-ribose (IC(50) = 95 mM), whereas D-glucose and L-fucose presented a lower inhibition, with IC(50) values as high as >0.5 and >0.2 M, respectively. On the other hand, D-fructose enhanced enzyme activity threefold, reaching a plateau of maximum specific activity between 0.2 and 0.4 M of this monosaccharide. Both effects, low inhibition and stimulation, caused by key fruit sugars (glucose and fructose), make this biocatalyst an interesting system in terms of its potential application for debittering fruit juices.