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Galactose transport systems in Streptococcus lactis.

J Thompson

    Journal of Bacteriology
    |November 1, 1980
    PubMed
    Summary

    Streptococcus lactis ML3 utilizes two distinct systems for galactose transport: a phosphotransferase system and an ATP-energized permease. The permease system shows higher affinity for galactose, while both systems exhibit similar transport rates.

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    Area of Science:

    • Microbiology
    • Molecular Biology
    • Biochemistry

    Background:

    • Streptococcus lactis ML3 possesses the ability to transport galactose, its growth sugar.
    • Galactose uptake occurs via two identified transport systems.

    Purpose of the Study:

    • To characterize the two distinct galactose transport systems in Streptococcus lactis ML3.
    • To elucidate the mechanisms and substrate specificities of these transport systems.

    Main Methods:

    • Utilized proton-conducting uncouplers to differentiate between transport systems.
    • Employed beta-galactoside analogs for inhibition and efflux studies.
    • Investigated the effects of iodoacetate and p-chloromercuribenzoate on sugar uptake.
    • Performed in vivo kinetic analysis by selectively generating energy sources.

    Main Results:

    • Galactose uptake is mediated by a phosphoenolpyruvate-dependent phosphotransferase system and an adenosine 5'-triphosphate-energized permease.
    • Proton-conducting uncouplers selectively inhibited the permease system.
    • The permease system demonstrated high affinity for galactose and specific beta-galactoside analogs, with structural hydroxyl groups being crucial.
    • The phosphotransferase system showed differential sensitivity to inhibitors, indicating distinct mechanisms.
    • Kinetic analysis revealed similar maximum transport rates but a 10-fold higher affinity for the permease system compared to the phosphotransferase system.

    Conclusions:

    • Streptococcus lactis ML3 employs two independent and distinct systems for galactose transport.
    • The permease system is the high-affinity, primary transporter for galactose, while the phosphotransferase system plays a complementary role.
    • Understanding these transport mechanisms is crucial for microbial metabolism and sugar uptake studies.

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