FIG. 1.

Transport of methylammonium (A and C) and glucose (B and D) by S. cerevisiae (see Materials and Methods). Strains for panels A and B were 23344c (wild type; squares), 31019b (Δmep1 Δmep2 Δmep3; circles), and NCM3243 (Δvph1; triangles), and strains for panels C and D were MM50 (wild type; squares), MM11 (Δstv1; open diamonds), MM108 (Δvma1; triangles), and MM112 (Δvph1 Δstv1; closed diamonds). (A) The initial concentration of [¹⁴C]methylammonium was 6 μM. Cells were grown in minimal medium with proline (10 mM) as the N source. The degree of concentration of methylammonium by strain 23344c was calculated assuming a cell volume of 70 μm³ and 10⁷ cells/ml/OD₆₀₀ (59). Inset, ¹⁴C-labeled products accumulated intracellularly 25 min after exposure to [¹⁴C]methylammonium. Products were separated by thin-layer chromatography and subjected to autoradiography. Lane 1, [¹⁴C]methylglutamine; lane 2, [¹⁴C]methylammonium; lane 3, wild type; lane 4, Δvph1. (B) The initial concentration of d-[1-¹⁴C]glucose was 170 μM. Cells were grown in modified YPD containing 0.05% glucose. (C) As for panel A except cells were grown in YPD–2% glucose. (D) As for panel B.