PURIFICATION OF PROTEIN DISULFIDE-ISOMERASE FROM A THERMOPHILIC FUNGUS

A protein disulfide isomerase (PDI) was purified to homogeneity from t he thermophilic fungus Humicola insolens by a rapid three-step procedu re, anion-exchange chromatography, concanavalin A-affinity chromatogra phy, and reverse phase high performance liquid chromatography. Forty-o nemug of PDI was obtained from 100 g of wet mycelium. Concanavalin A-S epharose chromatography is available for purification of the fungal PD I, indicating that the enzyme is also glycosylated like the yeast PDI. The fungal PDI exists as a dimer (2 x 60 kDa), has a pI of 3.5, and i s fairly heat-stable. The amino acid composition of the PDI is similar to those of yeast and bovine liver PDI, and the high content of acidi c amino acid residues agrees with the lower acidic pI.