Branched‐chain amino acid transport in Streptococcus mutans Ingbritt

Abstract

Leucine transport in glucose‐energized cells of Streptococcus mutans exhibited Michaelis‐Menten‐type kinetics at low extracellular concentrations, with a Kt, of 15.3 μM and a Vmax of 6.1 nmol/mg dry weight/min. At high extracellular leucine concentrations, the transmembrane diffusion of leucine was not saturable, indicating that passive diffusion becomes a significant mechanism of leucine transmembrane movement under these conditions. The proton motive force (PMF) was measured in glucose‐energized cells of S. mutans and was found to have a maximum value of 126 mV at an extracellular pH (pH0) of 5.0; this decreased to 45 mV at pH0 8.0. The intracellular accumulation of leucine was significant..