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Appl Environ Microbiol. 1986 January; 51(1): 95-100
Copyright © 1986, American Society for Microbiology. All Rights Reserved.

Energetics of Leucyl-Leucine Hydrolysis in Streptococcus cremoris Wg₂

Department of Microbiology, University of Groningen, 9751 NN Haren, The Netherlands

ABSTRACT

The hydrolysis of the dipeptide leucyl-leucine by whole cells of Streptococcus cremoris Wg₂ was dependent on the presence of the energy source lactose. Incubation of cells with uncouplers or ATPase inhibitors prevented the increase of peptidase activity upon the addition of lactose. Incubation with the ionophore nigericin resulted in decreased peptide hydrolysis activity, while incubation with valinomycin led to increased hydrolysis activity. In the presence of nigericin the pH component of the proton motive force was decreased, while the electrical potential was increased. With valinomycin, the electrical potential was collapsed and the pH was increased. When the external pH was decreased from 8 to 5, the rate of peptide hydrolyzing activity by whole cells increased with increasing pH component. In contrast, the peptide hydrolyzing activity in the cell extract decreased with decreasing external pH. These results indicate that the pH component of the proton motive force determines the leucyl-leucine hydrolyzing activity in S. cremoris Wg₂.

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