The reported cDNA sequence for phospholipase Cα encodes protein disulfide isomerase, isozyme Q-2 and not phospholipase-C

We have previously shown that the cDNA sequence published for the rat gene encoding phosphatidylinositol specific phospholipase Cα (1) may be identical to the sequence of a new isoform of protein disulfide isomerase, Isozyme Q2 (2). To determine whether the presumed phospholipase Cα gene encodes phospholipase C or protein disulfide isomerase, we have now expressed the cDNA in Escherichia coli and find that the 55.5 kDa protein that it synthesized contains no phopsholipase C activity. Moreover, an extract of Escherichia coli containing the expressed protein shows a concentration dependent increase in protein disulfide isomerase activity. The expressed protein is identical to protein disulfide isomerase, Isozyme Q2 on SDS-PAGE and by Western blot analysis. These current studies confirm that the published sequence of phospholipase Cα is, in fact, the sequence of protein disulfide isomerase, Isozyme Q2.