Uptake of methylamine via an inducible, energy-dependent transport system in the facultative methylotroph Arthrobacter P1

Abstract

Cytoplasmic membrane vesicles were prepared by a lysozyme-salt treatment from Arthrobacter P1 grown on methylamine as the carbon and energy source. In the presence of an ascorbate-phenazine methosulphate electron donor system, these vesicles accumulated methylamine in unmodified form by an inducible transport system. This system has a high affinity for methylamine (Kapp=20–25 μM). The effect of the ionophores valinomycin and nigericin combined with membrane potential (Δψ) and pH-gradient (ΔpH) measurements demonstrated that methylamine uptake is electrogenic and driven by the Δψ. Optimal activity is observed at pH 6.5 and 30°C. Methylamine uptake was not affected by the presence of ammonium ions but was inhibited by the primary amines ethylamine (competitively), propylamine, butylamine and benzylamine. In addition, formaldehyde and acetate, at a concentration of 1 mM, inhibited methylamine uptake almost completely. These compounds were shown to be non-competitive inhibitors. A strong inhibition observed in the presence of plumbagin could be relieved by addition of dithiothreitol. This indicates that the oxidation-reduction state of, probably, carrier dithiol-disulfide-groups is an important factor in methylamine translocation in Arthrobacter P1.