Driessen, Arnold J.M.

Jong, Steven de

Kodde, Jan

Konings, Wilhelmus

English

The pH dependence of transport of the neutral amino acids L-serine and L-alanine by membrane vesicles of Streptococcus cremoris have been studied in detail. The rates of four modes of facilitated diffusion (e.g., influx, efflux, exchange, and counterflow) of L-serine and L-alanine increase with increasing H+ concentration. Rates of artificially imposed electrical potential across the membrane (ΔΨ)-driven transport of L-serine and L-alanine show an optimum at pH 6 to 6.5. Under similar conditions, ΔΨ- and pH gradient across the membrane (ΔpH)-driven transport of L-leucine is observed within the pH range studied (pH 5.5 to 7.5). The effect of ionophores on the uptake of L-alanine and L-serine has been studied in membrane vesicles of S. cremoris fused with proteoliposomes containing beef heart mitochondrial cytochrome c oxidase as a proton motive force (Δp)-generating system. An increase in the initial rates of L-serine and L-alanine uptake is observed with decreasing pH, which is not consistent with the pH dependency of Δp. Nigericin, an ionophore that induced a nearly complete interconversion of ΔpH into ΔΨ, stimulated both the rate and the final level of L-alanine and L-serine uptake. Valinomycin, an ionophore that induced a collapse of ΔΨ with a noncompensating increase in ΔpH, inhibited L-alanine and L-serine uptake above pH 6.0 more efficiently than it decreased Δp. Experiments which discriminate between the effects of the internal pH and the driving force (ΔpH) on solute transport indicate that at high internal pH the transport systems for L-alanine and L-serine are inactivated. A unique relation exists between the internal pH and the initial rate of uptake of L-serine and L-alanine with an apparent pK of 7.0. The rate of L-alanine and L-serine uptake decreases with increasing internal pH. The apparent complex relation between the Δp and transport of L-alanine and L-serine can be explained by a regulatory effect of the internal pH on the activity of the L-serine and L-alanine carriers

ARTS repository - University of Groningen

Neutral Amino Acid Transport by Membrane Vesicles of Streptococcus cremoris Is Subject to Regulation by Internal pH

https://pure.rug.nl/ws/files/3390143/1987JBacteriolDriessen1.pdf

Neutral Amino Acid Transport by Membrane Vesicles of Streptococcus cremoris Is Subject to Regulation by Internal pH

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ARTS repository - University of Groningen