INDEPENDENCE OF THE CHAPERONE ACTIVITY OF PROTEIN DISULFIDE-ISOMERASEFROM ITS THIOREDOXIN-LIKE ACTIVE-SITE

Protein disulfide isomerase (PDI) alkylated at thiols of the thioredox in-like -CHC- active sites is devoid of isomerase activity, but its ch aperone-like activity to increase the reactivation yield and prevent t he aggregation of guanidine hydrochloride-denatured D-glyceraldehyde-3 -phospate dehydrogenase upon dilution is unimpaired. A peptide of 28 a mino acids markedly inhibits both the enzyme and the chaperone activit ies of PDI. The above results indicate that the -CGHC- active site is necessary for the isomerase activity but not required for the chaperon e activity of PDI, whereas the peptide binding site is essential for b oth activities.