Methylamine and ammonium transport systems in Rhizobium leguminosarum MNF3841
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As the sole source of nitrogen, methylamine supported the growth of a range of species of Rhizobium. The methylamine assimilatory system was inducible in R. leguminosarum MNF3841, whereas the capacity to utilize NH4+ as a nitrogen source was constitutive. An uptake system for [14C]methylamine (methylamine permease) was induced by growth of MNF3841 on methylamine or ethylamine. The uptake was sensitive to 2,4-dinitrophenol, azide and carbonyl cyanide m-chlorophenylhydrazone. The methylamine permease had a Km of 0.035 mM, a Vmax of 2.2 nmol min-1 (mg protein)-1 and a Ki for ammonium of 1.5 mM. Most of the [14C]methylamine accumulated by cells was rapidly incorporated into TCA-insoluble materials. An NH4+-sensitive methylamine-accumulating system distinct from the methylamine permease was demonstrated in ammonia-limited cells grown in continuous culture. This system, the ammonium permease, had a Km of 0.11 mM (for methylamine), a Ki for NH4+ of 0.007 mM and a Vmax, of 2.5 nmol min-1 (mg protein)-1. Methylamine was accumulated by chemostat-grown, N-limited cells and could exchange with unlabelled methylamine. Treatment with carbonyl cyanide m-chlorophenylhydrazone caused efflux of the accumulated methylamine, whereas high concentrations of NH4+ did not. Thus R. leguminosarum possesses a specific methylamine permease which is quite distinct from the ammonium permease.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||School of Environmental and Life Sciences|
|Publisher:||Society for General Microbiology|
|Copyright:||© 1984 SGM|
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