Regulatory role of δ-aminolevulic acid dehydratase in the dimorphic fungus Mucor rouxii

Abstract

1. 1. With the aim of finding a possible relationship between the known dimorphism phenomenon existing in the fungus Mucor rouxii and the biosynthesis of respiratory pigments, the activity of aminolevulic acid synthetase (ALA-S) and ALA-dehydratase (ALA-D) was studied in crude extracts and in 15,000 g supernatants of both mycelium and yeast-like cells. 2. 2. The activity of ALA-S was unusually high (3 nmol ALA/hr/mg protein) compared with that reported for other tissues and did not vary with the fungus morphology. 3. 3. Instead, ALA-D specific activity was found to be 16.5 nmol PBG/hr/mg protein in mycelium extracts, that is 7-fold greater than that measured in the yeast-like morphology (2.6 nmol PBG/hr/mg protein). 4. 4. It was of importance to determine the activity levels of ALA-D along with the morphogenic transition from yeast to mycelium. It was observed that the greatest change and enhancing of specific activity occurred 2 hr before the emergence of the germ tubes and was held constant up to the complete development of mycelium. 5. 5. Both hyphae formation and enhancement of ALA-D activity were diminished when cAMP was added to the culture shifted from the anaerobic atmosphere to air. 6. 6. These findings and preliminary studies on the characterization of M. rouxii ALA-D indicate that this enzyme plays a regulatory role in porphyrin biosynthesis in this fungus as well as a key function in the characteristic morphogenic transition.