FIG. 4.

Transport of methylammonium by N. crassa (A) and characterization of the products accumulated (B) (see Materials and Methods). (A) The initial concentration of [¹⁴C]methylammonium was 4 μM. Strains 74A (wild type; squares) and pvn2-53-19A (vma-1; triangles) were grown in modified Vogel's minimal medium with glucose (2%) as the carbon source and 10 mM NH₄Cl (open symbols) or 10 mM proline (closed symbols) as the sole nitrogen source. (B) Components of cell extracts (∼2,400 cpm) were separated by thin-layer chromatography and subjected to autoradiography. Lanes 1 to 4, strain 74A (wild type); lanes 5 to 8, strain pvn2-53-19A (vma-1). Extracts were prepared 1 min (lanes 1 and 5), 4 min (lanes 2 and 6), 10 min (lanes 3 and 7), and 25 min (lanes 4 and 8) after exposure to [¹⁴C]methylammonium (initial concentration, 5 μM). Cells were grown in Vogel's minimal medium with proline (10 mM) as the N source. Positions of [¹⁴C]methylammonium (CH₃NH₃⁺) and [¹⁴C]methylglutamine (CH₃-Gln) are indicated on the left.