Two different catalases present in cell-free extracts of the yeast Trigonopsis variabilis have been separated by dye-binding chromatography. Both enzymes, named TvC-I and TvC-II, behave as members of the "typical catalases" family: they have a broad pH activity profile and do not possess peroxidase activity, are quite stable when treated with ethanol/chloroform mixtures, are inhibited by azide and cyanide at micromolar concentrations, and inactivated by 3-amino-1,2,4-triazole. Both enzymes are not thermostable, being inactivated rapidly at 55 degreesC, whereas their pH stability profile is markedly different. TvC-I is highly tolerant to pH variations, being rapidly inactivated only at acidic pH values (2.0. or lower). Its half-life time (t(1/2)) is at least 50 h at pH values between 3.0 and 12.0 and about 2 h at pH 13.0. At variance, the pH stability of TvC-II is markedly lower, the enzyme being rapidly inactivated at pH values lower than 4.0 and higher than 10.0. The t(1/2) of TvC-II at pH values comprised between 6.0 and 10.0 is approximately 20 h, whereas at pH 4.0 and 5.0, t(1/2) increases to 77 and 45 h, respectively. TvC-II has been purified to homogeneity and characterized: the enzyme has an apparent molecular mass of about 230 kDa and is a tetramer with identical subunits. It is resistant to reduction by sodium dithionite, while its treatment with KCN resulted in a shift of the Soret band at 424 nm, appearance of a peak at 546 nm, and elimination of the peak at 632 nm. Peptides obtained by tryptic digestion of TvC-II have been analyzed by HPLC-MS: the deduced amino acid sequences have been used for searching similarity in a catalase sequence database built from SWISS-PROT. The best match has been obtained with the catalase A from Saccharomyces cerevisiae, showing about 50% of protein sequence coverage. (C) 2003 Elsevier Science Inc. All rights reserved.