Purification and immunological characterization with monoclonal antibodies

The purification of human placenta and rat liver protein disulphide-isomerase (PDI, EC 5.3.4.1) and the production of a panel of monoclonal antibodies against these proteins are described. The physical and enzymic properties of human PDI and rat PDI were similar; immunological characterization revealed the presence of unique, as well as shared, antigenic determinants. Although purified rat liver PDI was present as three forms differing slightly in Mr value, evidence was presented that the multiple forms represent proteolytic degradation products of a single 59000-Mr species. Purified human PDI had an apparent Mr of 61200. Two of the monoclonal antibodies against human PDI partially inactivated the enzyme, and one of these in indirect immunoprecipitation led to the precipitation of all glutathione: insulin transhydrogenase activity from a crude extract of human placenta. Results of immunofluorescence experiments with HT-29 human colon carcinoma cells were consistent with localization of PDI in the nuclear membrane and cell cytoplasm.