Protein disulfide isomerase may facilitate the efflux of nitrite derived S-nitrosothiols from red blood cells

Protein disulfide isomerase (PDI) is an abundant protein primarily found in the endoplasmic reticulum and also secreted into the blood by a variety of vascular cells. The evidence obtained here, suggests that PDI could directly participate in the efflux of NO from red blood cells (RBC). PDI was detected both in RBC membranes and in the cytosol. PDI was S-nitrosylated when RBCs were exposed to nitrite under similar to 50% oxygen saturation but not under similar to 100% oxygen saturation. Furthermore, it was observed that hemoglobin (Hb) could promote PDI S-nitrosylation in the presence of similar to 600 nM nitrite. In addition, three lines of evidence were obtained for PDI-Hb interactions: (1) Hb co-immunoprecipitated with PDI; (2) Hb quenched the intrinsic PDI fluorescence in a saturable manner; and (3) Hb-Fe(II)-NO absorption spectrum decreased in a [PDI]-dependent manner. Finally. PDI was detected on the surface RBC under similar to 100% oxygen saturation and released as soluble under similar to 50% oxygen saturation. The soluble PDI detected under similar to 50% oxygen saturation was S-nitrosylated. Based on these data it is proposed that PDI is taken up by RBC and forms a complex with Hb. Hb-Fe(II)-NO that is formed from nitrite reduction under similar to 50% 02, then transfers NO+ to either Hb-Cys beta 93 or directly to PDI resulting in S-nitroso-PDI which transverses the RBC membrane and attaches to the RBC surface. When RBCs enter tissues the S-nitroso-PDI is released from the RBC-surface into the blood where its NO is transferred into the endothelium thereby inducing vasodilation, suggesting local oxygen-dependent dynamic interplays between nitrite, NO and S-nitrosylation. (C) 2013 The Authors. Published by Elsevier By. Open access under CC BY-NC-ND license