Cat-3 activity increased during the growing and pre-stationary phase, adhesion of hyphae and growth of aerial hyphae. The enzyme was localized at the cell wall but also in mitochondria and the cytosol. Cat-3 activity increased with depletion of the carbon source, paraquat, light and singlet oxygen. Cat-3 is a homotetramer of 79 kDa subunits, probably containing a chlorin instead of protoheme IX. The tetramer pI is 4.80. The protein was slightly glycosylated. The enzyme was stable in organic solvents, high salt or SDS concentrations. Cat-3 was resistant to molar concentrations of H2O2. A Km of 74 mM was obtained with less than 100 mM H2O2 and of 209 mM at molar H2O2 concentrations. It exhibited no pH optimum and was inactivated by 3-amino-triazole, azide and hydroxylamine. KCN was a competitive inhibitor with I50 of 60 microM. Cat-3 is also modified by singlet oxygen giving rise to more acidic active conformers. The gene has two introns, codifies for a 719 amino acid polypeptide. It is 67% similar to Claviceps Cat1, 65% to Aspergillus nidulans CatB and 64% to A. fumigatus CatB and 53% to N. crassa Cat-1. Accumulation of the mRNA was observed at the pre-stationary growth phase. Accumulation of the mRNA by light was dependent on both 'white collar' transcription factors. Initiation sites and the polyadenilation site were determined. Paraquat regulated cat-3 expression at the transcriptional level.
Full conference title:
21st Fungal Genetics Conference
- Fungal Genetics Conference 21st (2000)