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Recent crystallographic studies suggested that fully liganded human hemoglobin can adopt multiple quaternary conformations that include the two previously solved relaxed conformations, R and R2, whereas fully unliganded deoxyhemoglobin may adopt only one T (tense) quaternary conformation. An important unanswered question is whether R, R2, and other relaxed quaternary conformations represent different physiological states with different oxygen affinities. Here, we answer this question by showing the oxygen equilibrium curves of single crystals of human hemoglobin in the R and R2 state. In this study, we have used a naturally occurring mutant hemoglobin C (j36 GIu-~Lys) to stabilize the R and R2 crystals. Additionally, we have refined the x-ray crystal structure of carbonmonoxyhemoglobin C, in the R and R2 state, to 1.4 and 1.8 A resolution, respectively, to compare precisely the structures of both types of relaxed states. Despite the large quaternary structural difference between the R and R2 state, both crystals exhibit similar noncooperative oxygen equilibrium curves with a very high affinity for oxygen, comparable with the fourth oxygen equilibrium constant (K4) of human hemoglobin in solution. One small difference is that the R2 crystals have an oxygen affinity that is 2-3 times higher than that of the R crystals. These results demonstrate that the functional difference between the two typical relaxed quaternary conformations is small and physiologically less important, indicating that these relaxed conformations simply reflect a structural polymorphism of a high affinity relaxed state. [ABSTRACT FROM AUTHOR]

Summary: Background: Epithelial neutrophil-activating peptide 78 (ENA-78) and interferon -inducible protein 10 (IP10) belong to the CXC chemokine family and are considered to be important factors in idiopathic pulmonary fibrosis (IPF). Idiopathic nonspecific interstitial pneumonia (NSIP) and IPF are the two largest subsets of idiopathic interstitial pneumonias (IIP). In patients with NSIP, the prognosis is generally good compared with IPF. Therefore, the pathogenesis of NSIP seems to be different from that of IPF, but this remains unclear. The aim of the present study was to evaluate the contribution of ENA-78 and IP10 in the two diseases. Methods: We measured the levels of ENA-78 and IP10 in serum and bronchoalveolar lavage fluid (BALF) of patients with IPF (), idiopathic NSIP () and healthy subjects () by enzyme-linked immunosorbent assays. Results: The level of ENA-78 in BALF was significantly higher in IPF patients than in NSIP patients and controls. Serum levels of ENA-78 and BALF levels of IP10 in NSIP patients were significantly higher than in patients with IPF and controls. In BALF of patients with NSIP, IP10 level significantly correlated with the absolute number of lymphocytes. In IPF patients, BALF IP10 levels also correlated with the proportion of lymphocytes in BALF. Conclusion: Our results show distinct profiles of CXC chemokines in IPF and NSIP, and suggest that these chemokines play an important role in inflammatory cell recruitment into the lung in patients with IIP. [Copyright &y& Elsevier]