The monoclonal anti-PDI Ab RL90 cross-reacts with ERp57 in the Di-E-GSSG assay. (A) Lack of cross- reactivity by Western blot to ERp57. (B) The inhibition of PDI. (C) The inhibition of ERp57 by RL90, at 10 μg/mL and 30 μg/mL relative to an isotype specific monoclonal mouse IgG2a Ab (30 μg/mL); 60 μg/mL did not provide more inhibition of PDI or ERp57 with the curves overlapping with the curves for 30 μg/mL. The amount of EGSH formed over 120 seconds from Di-E-GSSG is shown with the enzyme added at ∼ 20 seconds.