Platelet surface ERp57 activity increases with platelet activation. (A) Conversion of Di-E-GSSG to EGSH increases with platelet activation. Effect of the inhibitory Mab1 and non-inhibitory Mab2 on nonactivated platelets (B) and activated platelets (C). The curves are from the combined data from 3 different experiments. Gel-filtered platelets (4 × 10⁸/mL) were activated with α-thrombin (0.5 U/mL) for 10 minutes. The antibodies were then added for 10 minutes at the concentrations indicated. Di-E-GSSG with DTT was added to give a final platelet concentration of 4 × 10⁷/mL and Di-E-GSSG and DTT concentration of 150 nM and 5 µM, respectively. Conversion of Di-E-GSSG to EGSH was monitored over time in a Spectra Max M2 fluorimeter (Molecular Devices) as previously described¹²  with the platelets present.²⁶