Porphyrin biosynthesis intermediates are not regulating delta-aminolevulinic acid transport in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, as in all eukaryotic organisms, delta-aminolev ulinic acid (ALA) is a precursor of porphyrin biosynthesis, a very finely r egulated pathway. ALA. enters yeast cells through the gamma-aminobutyric ac id (GABA) permease Uga4. The incorporation of a metabolite into the cells m ay be a limiting step for its intracellular metabolization. To determine th e relationship between ALA transport and ALA metabolization, ALA incorporat ion was measured in yeast mutant strains deficient in the delta-aminolevuli nic acid-synthase, uroporphyrinogen III decarboxylase, and ferrochelatase, three enzymes involved in porphyrin biosynthesis. Results presented here sh owed that neither intracellular ALA nor uroporphyrin or protoporphyrin regu lates ALA incorporation, indicating that ALA uptake and its subsequent meta bolization are not related to each other. Thus a key metabolite as it is, A LA does not have a transport system regulated according to its role. (C) 20 00 Academic Press.