Toxicity of oxalysine and oxalysine-containing peptides against Candida albicans: regulation of peptide transport by amino acids.

A lysine antimetabolite, L-4-oxalysine [H2NCH2CH2OCH2CH(NH2)COOH], and oxalysine-containing di-, tri-, tetra- and pentapeptides inhibited growth of Candida albicans H317. Micromolar amounts of amino acids were found to overcome ammonium repression of the di- and tripeptide transport system(s) in strain H317. Several amino acids increased the toxicity of oxalysine-containing di- and tripeptides for C. albicans with little or no increase in toxicity of oxalysine or oxalysine-containing tetra- and pentapeptides. L-Lysine completely reversed the toxicity of oxalysine by competing with the transport of oxalysine into the cells. In contrast, L-lysine increased the toxicity of oxalysine-containing di- and tripeptides, but had no effect on the toxicity of oxalysine-containing tetra- and pentapeptides. Incubation of cells with L-lysine for 4 h resulted in a 15-fold increase in the rate of transport of radiolabelled dileucine, indicating that increased sensitivity of C. albicans to some toxic peptides in the presence of L-lysine may be attributed to an increased rate of transport of these peptides. Our results indicate that the dipeptide and tripeptide transport system(s) of C. albicans are regulated by micromolar amounts of amino acids in a similar fashion to the regulation of peptide transport in Saccharomyces cerevisiae and that multiple peptide transport systems differentially regulated by various nitrogen sources and amino acids exist in C. albicans.