Acidic pH conditions induce dissociation of the haem from the protein and destabilise the catalase isolated from <Emphasis Type="Italic">Aspergillus terreus</Emphasis>

The stability (half-life, t_½) of the large catalase (CAT) isolated from Aspergillus terreus was decreased under acidic conditions (maximum t_½ ~8.5 months at pH ≤ 6) versus alkaline conditions (t_½ ~15 months at pH 8–12). Acidic conditions induce the dissociation of haem from CAT, as revealed from a reduction in the Soret peak intensity at 405 nm and an increase in the peak current at Fe³⁺/Fe²⁺ redox potentials. This increase in current is attributed to the facile electron transfer from the free haem generated on the electrode surface as a result of its disintegration from the insulating protein matrix. The haem isolated from CAT at acidic condition was reconstituted with apo-CAT at alkaline denaturing conditions to regenerate the CAT activity.