Oxidized dimeric Scapharca inaequivalvis. Co-driven perturbation of the redox equilibrium.

The dimeric hemoglobin isolated from Scapharca inaequivalvis, HbI, is notable for its highly cooperative oxygen binding and for the unusual proximity of its heme groups. We now report that the oxidized protein, an equilibrium mixture of a dimeric high spin aquomet form and a monomeric low spin hemichrome, binds ferrocyanide tightly which allows for internal electron transfer with the heme iron. Surprisingly, when ferricyanide-oxidized HbI is exposed to CO, its spectrum shifts to that of the ferrous CO derivative. Gasometric removal of CO leads to the oxidized species rather than to ferrous deoxy-HbI. At equilibrium, CO binds with an apparent affinity (p50) of about 10-25 mm of Hg and no cooperativity (20 degrees C, 10-50 mM buffers at pH 6.1). The kinetics of CO binding under pseudo-first order conditions are biphasic (t1/2 of 15-50 s at pH 6.1). The rates depend on protein, but not on CO concentration. The nitrite-oxidized protein is not reduced readily in the presence of CO unless one equivalent of ferrocyanide, but not of ferricyanide, is added. We infer that ferrocyanide, produced in the oxidation reaction, is tightly bound to the protein forming a redox couple with the heme iron. CO shifts the redox equilibrium by acting as a trap for the reduced heme. The equilibrium and kinetic aspects of the process have been accounted for in a reaction scheme where the internal electron transfer reaction is the rate-limiting step

Effect of heme and non-heme ligands on subunit dissociation of normal and carboxypeptidase-digested hemoglobin. Gel filtration and flash photolysis studies.

The dissociation of normal and carboxypeptidase-digested human hemoglobin has been studied by gel filtration under several experimental conditions. These include (a) different derivatives, notably deoxy-, oxy-, and CO-hemoglobin, (b) changes in solvent composition and in pH, and (c) addition of inositol hexaphosphate. In normal hemoglobin, in agreement with previous results, the deoxygenated derivative is much less dissociated than the oxy or CO ones. This difference is observed also in some of the digested hemoglobins, but tends to vanish in those proteins in which, as a result of extensive digestion, the conformational change accompanying ligand binding is abolished. The dissociation of normal and digested hemoglobins is affected by solvent composition, is at a minimum at pH near 8, and is decreased by the addition of inositol hexaphosphate. Parallel flash photolysis experiments, performed under conditions identical with those used in the gel filtration studies, indicate that the appearance of quickly reacting material parallels dissociation into dimers in normal hemoglobin. Both in normal and digested hemoglobins conditions which decrease dissociation decrease the fraction of rapidly reacting material. In the digested hemoglobins the fraction of rapidly reacting material may be much higher than can be accounted for by the amount of dimers, indicating in these cases that the tetramers may be rapidly reacting. The data point once again to the critical role of the COOH-terminal residues in maintaining the subunit structure of hemoglobin and the interaction effects associated with it

Neuromyelitis optica spectrum disorders. Comparison according to the phenotype and serostatus

Objective: To (1) determine the value of the recently proposed criteria of neuromyelitis optica (NMO) spectrum disorder (NMOSD) that unify patients with NMO and those with limited forms (NMO/LF) with aquaporin-4 immunoglobulin G (AQP4-IgG) antibodies; and (2) investigate the clinical significance of the serologic status in patients with NMO. Methods: This was a retrospective, multicenter study of 181 patients fulfilling the 2006 NMO criteria (n = 127) or NMO/LF criteria with AQP4-IgG (n = 54). AQP4-IgG and myelin oligodendrocyte glycoprotein immunoglobulin G (MOG-IgG) antibodies were tested using cell-based assays. Results: Patients were mainly white (86%) and female (ratio 6.5:1) with median age at onset 39 years (range 10-77). Compared to patients with NMO and AQP4-IgG (n = 94), those with NMO/LF presentedmore often with longitudinally extensive transverse myelitis (LETM) (p<0.001), and had lower relapse rates (p = 0.015), but similar disability outcomes. Nonwhite ethnicity and optic neuritis presentation doubled the risk for developing NMO compared with white race (p = 0.008) or LETM presentation (p = 0.008). Nonwhite race (hazard ratio [HR] 4.3, 95% confidence interval [CI] 1.4-13.6) and older age at onset were associated with worse outcome (for every 10-year increase, HR 1.7, 95% CI 1.3-2.2). Patients with NMO and MOG-IgG (n = 9) had lower female: male ratio (0.8:1) and better disability outcome than AQP4-IgG-seropositive or double-seronegative patients (p<0.001). Conclusions: In patients with AQP4-IgG, the similar outcomes regardless of the clinical phenotype support the unified term NMOSD; nonwhite ethnicity and older age at onset are associated with worse outcome. Double-seronegative and AQP4-IgG-seropositive NMO have a similar clinical outcome. The better prognosis of patients with MOG-IgG and NMO suggests that phenotypic and serologic classification is useful

Consensus on early detection of disease progression in patients with multiple sclerosis

BackgroundEarly identification of the transition from relapsing-remitting multiple sclerosis (RRMS) to secondary progressive MS (SPMS) can be challenging for clinicians, as diagnostic criteria for SPMS are primarily based on physical disability and a holistic interpretation.ObjectiveTo establish a consensus on patient monitoring to identify promptly disease progression and the most useful clinical and paraclinical variables for early identification of disease progression in MS.MethodsA RAND/UCLA Appropriateness Method was used to establish the level of agreement among a panel of 15 medical experts in MS. Eighty-three items were circulated to the experts for confidential rating of the grade of agreement and recommendation. Consensus was defined when ≥66% agreement or disagreement was achieved.ResultsConsensus was reached in 72 out of 83 items (86.7%). The items addressed frequency of follow-up visits, definition of progression, identification of clinical, cognitive, and radiological assessments as variables of suspected or confirmed SPMS diagnosis, the need for more accurate assessment tools, and the use of promising molecular and imaging biomarkers to predict disease progression and/or diagnose SPMS.ConclusionConsensus achieved on these topics could guide neurologists to identify earlier disease progression and to plan targeted clinical and therapeutic interventions during the earliest stages of SPMS