title: TRK2 is not a low-affinity potassium transporter in Saccharomyces cerevisiae.
abstract: TRK1 and TRK2 encode proteins involved in K+ uptake in Saccharomyces cerevisiae. A kinetic study of Rb+ influx in trk1 TRK2, trk1 TRK2D, and trk1 trk2 mutants reveals that TRK2 shows moderate affinity for Rb+. K(+)-starved trk1 delta TRK2 cells show a low-affinity component accounting for almost the total Vmax of the influx and a moderate-affinity component exhibiting a very low Vmax. Overexpression of TRK2 in trk1 delta TRK2D cells increases the Vmax of the moderate-affinity component, and this component disappears in trk1 delta trk2 delta cells. In contrast, the low-affinity component of Rb+ influx in trk1 delta TRK2 cells is not affected by mutations in TRK2. Consistent with the different levels of activity of the moderate-affinity Rb+ influx, trk1 delta TRK2 cells grow slowly in micromolar K+, trk1 delta TRK2D cells grow rapidly, and trk1 delta trk2 delta cells fail to grow. The existence of a unique K+ uptake system composed of several proteins is also discussed.
authors.affiliation: Departamento de Microbiología, Escuela Técnica Superior de Ingenieros Agrónomos, Córdoba, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Ramos
authors.forename: R
authors.initials: R
authors.lastname: Alijo
authors.forename: R
authors.initials: R
authors.lastname: Haro
authors.forename: A
authors.initials: A
authors.lastname: Rodriguez-Navarro
mesh_terms: D001386:Azides / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D027682:Cation Transport Proteins; D005656:Fungal Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D001386:Azides; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D005656:Fungal Proteins; D008565:Membrane Proteins; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; C085258:TRK2 protein, S cerevisiae; C068664:TRK1 protein, S cerevisiae; D012413:Rubidium; D011188:Potassium