The ligninolytic enzyme system of Phanerochaete chrysosporium decolorizes several recalcitrant dyes. Three isolated lignin peroxidase isoenzymes (LiP 4.65, LiP 4.15, and LiP 3.85) were compared as decolorizers with the crude enzyme system from the culture medium. LiP 4.65 (H2), LiP 4.15 (H7), and LiP 3.85 (118) were purified by chromatofocusing, and their kinetic parameters were found to be similar. Ten different types of dyes, including azo, triphenyl methane, heterocyclic, and polymeric dyes, were treated by the crude enzyme preparation. Most of the dyes lost over 75% of their color, only Congo red, Poly R-478, and Poly T-128 were decolorized less than the others, 54, 46, and 48%, respectively. Five different dyes were tested for decolorization by the three purified isoenzymes. The ability of the isoenzymes to decolorize the dyes in the presence of veratryl alcohol was generally comparable to that of the crude enzyme preparation, suggesting that lignin peroxidase plays a major role in the decolorization and that manganese peroxidase is not required to start the degradation of these dyes. In the absence of veratryl alcohol, the decolorization activity of the isoenzymes was in most cases dramatically reduced. However, LiP 3.85 was still able to decolorize 20%o of methylene blue and methyl orange and as much as 60% of toluidine blue 0, suggesting that at least some dyes can function as substrates for isoenzyme LiP 3.85 but not to the same extent for LiP 4.15 or LiP 4.65. Thus, the isoenzymes have different specificities towards dyes as substrates.

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A series of truncated proteins from a thermostable Bacillus stearothermophilus alpha-amylase was prepared to study the importance of the extension in the C-terminus compared with other liquefying Bacillus alpha-amylases. The mutations introducing new translation termination sites shortened the 515 amino acid residue-long wild type enzyme by 17, 32, 47, 73 or 93 residues. The longer the truncation, the lower the specific activity of the enzyme. Only the two longest mutant proteins were active: the specific activity of the 498 residue variant was 97% and protein 483 was 36% that of the parental enzyme. The Km values of starch hydrolysis changed from 1.09 for wild type enzyme to 0.35 and 0.21 for mutants 498 and 483, respectively, indicating altered substrate binding. The mutant enzymes had almost identical pH and temperature optima with the wild type amylase, but enhanced thermal stability and altered end product profile. The consequences of the truncation to the structure and function of the enzymes were explored with molecular modeling. The liquefying amylases seem to require approximately 480 residues to be active, whereas the C-terminal end of B.stearothermophilus amylase is required for increased activity.

The relationship between structure, activity, and stability of the thermostable Bacillus stearothermophilus alpha-amylase was studied by site-directed mutagenesis of the three most conserved residues. Mutation of His-238 to Asp involved in Ca2+ and substrate binding reduced the specific activity and thermal stability, but did not affect the pH and temperature optima. Replacement of Asp-331 by Glu in the active site caused almost total inactivation. Interestingly, in prolonged incubation this mutant enzyme showed an altered end-product profile by liberating only maltose and maltotriose. Conservative mutation of the conserved Arg-232 by Lys, for which no function has yet been proposed, resulted in lowered specific activity: around 12% of the parental enzyme. This mutant enzyme had a wider pH range but about the same temperature optimum and thermal stability as the wild-type enzyme. Results obtained with different mutants were interpreted by computer aided molecular modeling.