SITE-DIRECTED MUTAGENESIS OF THE LOWER PARTS OF THE MAJOR SUBSTRATE CHANNEL OF YEAST CATALASE-A LEADS TO HIGHLY INCREASED PEROXIDATIC ACTIVITY

Five single replacement mutants of catalase A from Saccharomyces cerev isiae were prepared (F148V, F149V, F156V, F159V, and V111A), The excha nges were expected to relieve steric constraints in the lowest part of the major substrate channel, The overall stability of the isolated en zymes is unaffected by the respective amino acid exchanges, but some m odifications lead to decreased protohaem binding, All isolated mutants (most pronounced the V111A-species) show decreased catalatic and mark edly increased peroxidatic activity, both with aliphatic and aromatic substrates, These effects can in part be explained by steric effects, but also reveal destabilisation of compound I.