Lactose-Hydrolyzing Enzymes of Lactobacillus Species1

β-Galactosidase (β-gal, EC 3.2.1.23) and β-D-phosphogalactoside galactohydrolase (β-Pgal) activities were observed in all of 13 Lactobacillus species studied except L. casei and L. buchneri . Only the latter enzyme was detected in nine strains of L. casei . The β-gal from L. thermophilus and the β-Pgal from L. casei were purified and characterized. In comparison with β-gal, the β-Pal was slightly less active ( V max values were 28.9 and 50.0 μmoles per mg per min, respectively), but the substrate affinitives were similar ( K m values were 1.69 × 10 -3 M and 1.59 × 10 -3 M, respectively). Although the two enzymes had similar amino acid compositions, the molecular weight of β-gal was 5.4 × 10 5 and that of β-Pgal was 1.3 × 10 5 . The β-gal from L. thermophilus and the β-Pgal from L. casei had optimal temperature and p H activity values of 55 C at p H 6.2 and 37 C at p H 5.0, respectively. The complete absence of β-gal from a homofermentative Lactobacillus species of industrial importance is further evidence of the heterogeneity of this genus.