After reading many 2-DE-based articles featuring lists of the differentially expressed proteins, one starts experiencing a disturbing déjà vu. The same proteins seem to predominate regardless of the experiment, tissue or species. To quantify the occurrence of individual differentially expressed proteins in 2-DE experiment reports, we compiled the identities of differentially expressed proteins identified in human, mouse, and rat tissues published in three recent volumes of Proteomics and calculated the appearance of the most predominant proteins in the dataset. The most frequently identified protein is a highly abundant glycolytic enzyme enolase 1, differentially expressed in nearly every third experiment on both human and rodent tissues. Heat-shock protein 27 (HSP27) and heat-shock protein 60 (HSP60) were differentially expressed in about 30 percent of human and rodent samples, respectively. Considering protein families as units, keratins and peroxiredoxins are the most frequently identified molecules, with at least one member of the group being differentially expressed in about 40 percent of all experiments. We suggest that the frequent identification of these proteins must be considered in the interpretation of any 2-DE studies. We consider if these commonly observed changes represent common cellular stress responses or are a reflection of the technical limitations of 2-DE.

Hepcidin is a major regulator of iron metabolism. Hepcidin-based therapeutics/ diagnostics could play roles in hematology in the future, and thus, hepcidin transport is crucial to understand. In this study, we identify ␣ 2 -macroglobulin (␣ 2 -M) as the specific hepcidin-binding molecule in blood. Interaction of 125 I-hepcidin with ␣ 2 -M was identified using fractionation of plasma proteins followed by native gradient polyacrylamide gel electrophoresis and mass spectrometry. IntroductionThe hormone hepcidin plays a role in orchestrating iron metabolism. [1][2][3][4][5][6][7][8][9][10][11][12] This peptide, originally discovered in urine as a bactericidal molecule, 13 was later shown to be a regulator of iron metabolism. 3,5 In fact, it plays an important role in conditions of altered iron demand. 3,5 The function of hepcidin is regulation of transmembrane iron transport. 4,5 Hepcidin binds to its cell surface receptor, ferroportin (solute carrier family 40 [iron-regulated transporter], member 1), leading to internalization and degradation of the protein complex by the lysosome. 1 Because ferroportin enables iron efflux from enterocytes, hepatocytes, and macrophages, its internalization after hepcidin binding leads to decreased iron release. 1 Hence, the hepcidin-mediated decrease in ferroportin iron export from enterocytes into blood leads to depressed intestinal iron absorption. 3,4 At the same time, iron export from hepatocytes and macrophages is blocked, which further decreases serum iron. [3][4][5] Hepcidin also plays a role during inflammation, infection, and cancer. [3][4][5] Under these conditions, iron is shifted from the circulation into stores, making it less available. 3 In anemia and hypoxia, hepcidin regulates iron availability for erythropoiesis. In the future, hepcidin may find a place in treating disease states. [3][4][5] Furthermore, hepcidin is predicted to become an indicator of body iron stores.We investigated the presence of plasma hepcidin-binding molecules because the identification of such entities will provide new insights into hepcidin function. Indeed, it is known that many hormones are transported in the blood by carrier molecules, 14-16 but a specific hepcidin-binding protein has not been identified. Hence, knowledge of hepcidin transport is essential for understanding its distribution and may be important for its measurement in plasma.In this study, we incubated blood plasma with 125 I-labeled human hepcidin and then separated plasma proteins using native electrophoresis. For the identification of these molecules, the complexes were purified using a native 2-dimensional separation technique with identification by mass spectrometry. 17 We identified ␣ 2 -macroglobulin (␣ 2 -M) as the specific hepcidin-binding molecule in plasma. Methods Chemicals, plasma, and serumChemicals were from Sigma-Aldrich (St Louis, MO). Blood was obtained from healthy volunteers (2 females, 3 males) after the study was approved by the Ethics Committee (Institute of Hematology and Blood Transfusion, Prague...