The gene encoding an alpha-l-arabinofuranosidase that could biotransform ginsenoside Rc {3-O-[similar to-d-glucopyranosyl-(1-2)-similar to-d-glucopyranosyl]-20-O-[alpha-l-arabinofuranosyl-(1-6)-not approximate to-d-glucopyranosyl]-20(S)-protopanaxadiol} to ginsenoside Rd {3-O-[similar to-d-glucopyranosyl-(1-2)-similar to-d-glucopyranosyl]-20-O-similar to-d-glucopyranosyl-20(S)-protopanaxadiol} was cloned from a soil bacterium, Rhodanobacter ginsenosidimutans strain Gsoil 3054(T), and the recombinant enzyme was characterized. The enzyme (AbfA) hydrolyzed the arabinofuranosyl moiety from ginsenoside Rc and was classified as a family 51 glycoside hydrolase based on amino acid sequence analysis. Recombinant AbfA expressed in Escherichia coli hydrolyzed non-reducing arabinofuranoside moieties with apparent K (m) values of 0.53 +/- 0.07 and 0.30 +/- 0.07 mM and V (max) values of 27.1 +/- 1.7 and 49.6 +/- 4.1 mu mol min(-1) mg(-1) of protein for p-nitrophenyl-alpha-l-arabinofuranoside and ginsenoside Rc, respectively. The enzyme exhibited preferential substrate specificity of the exo-type mode of action towards polyarabinosides or oligoarabinosides. AbfA demonstrated substrate-specific activity for the bioconversion of ginsenosides, as it hydrolyzed only arabinofuranoside moieties from ginsenoside Rc and its derivatives, and not other sugar groups. These results are the first report of a glycoside hydrolase family 51 alpha-l-arabinofuranosidase that can transform ginsenoside Rc to Rd.