FIG. 3.

Formation of nicotine blue and l-[¹⁴C]nicotine uptake in the presence of l- and d-amino acids. (A) To A. nicotinovorans/pAO1 stationary-phase bacteria, a 100 μM concentration of each of the following amino acids was added: bar 2, l-Glu; bar 3, l-Ser; bar 4, l-Arg; bar 5, l-Lys; bar 6, l-Ala; bar 7, l-His; bar 8, d-Pro; bar 9, d-Lys; bar 10, d-Arg; bar 11, d-His; bar 12, d-Ala; bar 13, d-Ser; bar 14, D, l-Phe; and bar 15, l-Pro. The cultures were induced with 50 μM l-nicotine, and nicotine blue formation was monitored after 3 h. Bar 1, nicotine blue formation in the presence of nicotine only. (B) Concentration-dependent effects of l-Pro and d-Arg on the formation of nicotine blue. (C) l-[¹⁴C]nicotine (1.5 μCi) was added to the A. nicotinovorans cultures in the absence of amino acids (crosses) or in the presence of 1 mM l-Pro (squares) or 1 mM d-Arg (triangles), and the time-dependent accumulation of radioactivity by the bacteria was determined as described in Materials and Methods.