PURIFICATION AND CHARACTERIZATION OF 2 PHOSPHOGLUCOMUTASES FROM LACTOCOCCUS-LACTIS SUBSP LACTIS AND THEIR REGULATION IN MALTOSE-UTILIZING AND GLUCOSE-UTILIZING CELLS

Two distinct forms of phosphoglucomutase were found in Lactococcus lac tis subsp. lactis, strains 19435 and 65.1, growing on maltose: beta-ph osphoglucomutase (beta-PGM), which catalyzes the reversible conversion of beta-glucose 1-phosphate to glucose 6-phosphate in the maltose cat abolism, and alpha-phosphoglucomutase (alpha-PGM). beta-PGM was purifi ed to more than 90% homogeneity in crude cell extract from maltose gro wn lactococci, and polyclonal antisera to the enzyme were prepared. Th e molecular mass of beta-PGM was estimated by gel filtration to be 28 kDa; its isoelectric point was 4.8. The corresponding values for alpha -PGM were 65 kDa and 4.4, respectively. The expression of both PGM enz ymes was investigated under different growth conditions. The specific activity and amount of beta-PGM per milliliter of cell extract increas ed with time in lactococci grown on maltose, but the enzyme was absent in lactococci grown on glucose, indicating enzyme synthesis to be ind uced by maltose in the growth medium. When glucose was added to maltos e-grown lactococci, both the specific activity and amount of beta-PGM per milliliter of cell extract decreased rapidly. This suggests that s ynthesis of beta-PGM is repressed by glucose in the medium. Although t he specific activity of alpha-PGM did not change during growth on malt ose or glucose, lactococcal strain 19435 showed a much higher specific activity of both alpha- and beta-PGM than strain 65.1 when grown on m altose.