Regulatory role of ALA-S and ALA-D in a haem-deficient mutant of Saccharomyces cerevisiae

Abstract

The biochemical characteristics of a haem-deficient mutant strain B231 of Saccharomyces cerevisiae isolated from D273-10B strain are described. B231 strain accumulates substantial amounts of 5-aminolevulinic acid (ALA) and uroporphyrin III (uro III). This pattern of porphyrins accumulation is due to both a defect in uroporphyrinogen decarboxylase (Uro-D) activity and an enhancement of porphobilinogenase (PBGase) activity. ALA accumulation would indicate that feed-back control by haem is not operating in this strain. ALA synthase (ALA-S), ALA-dehydrase (ALA-D) and PBGase activities; intracellular content of ALA (I-ALA) and porphyrins (I-porphyrins) were examined during the different phases of growth. Both accumulation of metabolites and enzyme activities reached their maximum values at 20 hrs. of growth, when glucose concentration in the medium fell to zero. Evidence for negative feed-back control on ALA-S and ALA-D by heme are provided by the observations of both enhanced I-ALA accumulation and increased ALA-D activity (2.5 times) in the mutant strain. Our results would indicate that both ALA-S and ALA-D can be considered regulatory enzymes in yeast.