Carbon and nitrogen sources regulate delta-aminolevulinic acid and gamma-aminobutyric acid transport in Saccharomyces cerevisiae.

Evidence has been obtained showing that transport of delta-aminolevulinic acid (ALA), a precursor of porphyrin biosynthesis in Saccharomyces cerevisiae, is mediated by the gamma-aminobutyric acid (GABA)-specific permease, UGA4. In yeast GABA is also incorporated by the general amino acid permease (GAP1) and the specific proline permease (PUT4). The aim of the present work was to carry out a comparative study on the regulation of ALA and GABA transport to confirm our proposal that both compounds share the UGA4 permease. ALA and GABA uptake were measured in cells grown on minimal media with different carbon and/or nitrogen sources. To study the effect of the carbon source on UGA4 permease, ALA and GABA incorporation were measured in D27 strain, lacking GAP1 permease, and grown in proline as the sole nitrogen source, so the activity of PUT4 permease was negligible. The effect of the nitrogen source on UGA4 permease was studied measuring ALA and GABA uptake rates in cells from media with ammonium, proline and urea as nitrogen sources. It was found that the regulation by the carbon source was similar on ALA and GABA transport; they depend equally on the energetic conditions of the cells. Moreover, regulation by the nitrogen source on ALA and GABA uptake was also similar, and identical to that described already for UGA4 permease. These results are further evidence that both compounds, ALA and GABA, share the GABA-specific permease, UGA4.