The present invention relates to protein disulfide isomerases which are encoded by a nucleic acid sequence which hybridizes with (i) the DNA sequence of SEQ ID NO:1 or (ii) the DNA sequence of SEQ ID NO:2, under the following conditions: presoaking in 5.times.SSC and prehybridizing for 1 h at .about.40.degree. C. in a solution of 5.times.SSC, 5.times.Denhardt's solution, 50 mM sodium phosphate, pH 6.8, and 50 .mu.g of denatured sonicated calf thymus DNA, followed by hybridization in the same solution supplemented with 50 .mu.Ci 32-P-dCTP labelled probe for 18 h at .about.40.degree. C. followed by washing three times in 2.times.SSC, 0.2% SDS at 40.degree. C. for 30 minutes; and fragments thereof. The present invention also relates to DNA sequences encoding the protein disulfide isomerases, compositions comprising said protein disulfide isomerases and methods of use thereof.