Abstract
Abstract β-Galactosidase (β-gal) and phospho-β-galactosidase (P-β-gal) from 33 strains belonging to different species of Leuconostoc have been investigated. P-β-gal was not detected, suggesting that the lactose transport system by translocation (PEPP-TS) is not functional in Leuconostoc. A great number of strains possess a high level of β-gal in the presence of glucose. Characterization of β-gal from several strains of Leuconostoc, in comparison with an industrial strain of S. thermophilus which was used as a reference, showed that the β-gal of Leuconostoc strains has a pH optimum at 7.2. The temperature optimum varied with the strain, ranging from 43 to 58 °C. The Km values of the enzymes on substrate o-nitrophenyl-β- d -galactopyranoside (ONPG) varied from 0.68 to 4.72 m m . The Leuconostoc β-gal had a lower affinity for lactose than that of S. thermophilus. Comparison of SDS-PAGE protein profiles for a Lac− mutant and its wild Lac+ parental strain allowed the apparent molecular weight of β-gal to be estimated at approximately 80 000 for Leuc. mesenteroides subsp. mesenteroides, which is different from that of the β-gal of Leuconostoc lactis.
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