Ozone model for bonding of an O2 to heme in oxyhemoglobin. (49/1729)

Several rather different models of the Fe-o2 bond in oxyhemoglobin have previously been proposed, none of which provide a satisfactory explanation of several properties. We propose a new model for the bonding of an O2 to the Fe of myoglobin and hemoglobin and report ab initio generalized valence bond and configuration interaction calculations on FeO2 that corroborate this model. Our model is based closely upon the bonding in ozone which recent theoretical studies have shown to be basically a biradical with a singlet state stabilized by a three-center four-electron pi bond. In this model, the facile formation and dissociation of the Fe-O2 bond is easily rationalized since the O2 always retains its triplet ground state character. The ozone model leads naturally to a large negative electric field gradient (in agreement with Mossbauer studies) and to z-polarized (perpendicular to the heme) charge transfer transitions. It also suggests that the 1.3 eV transition, present in HbO2 and absent in HbCO, is due to a porphyrin-to-Fe transition, analogous to that of ferric hemoglobins (e.g., HbCN).  (+info)

Triple-site antigen capture ELISA for human myoglobin can be more effective than double-site assay. (50/1729)

Using a panel of monoclonal antibodies against human myoglobin (Mb), we have shown that the sensitivity of antigen-capture ELISA can be significantly increased by simultaneous immobilization of two cooperating capture monoclonal antibodies on a solid phase. This method ("triple-site ELISA") uses three monoclonal antibodies to different epitopes of the same antigen (two capture/one tracer) unlike the traditional double-site assay using one capture and one tracer monoclonal antibody. We developed double- and triple-site ELISA for Mb by varying the capture and tracer monoclonal antibodies. Triple-site assays showed 4-6-fold increase in sensitivity compared to the double-site assays. A model for this effect is suggested; according to the model, in triple-site ELISA, high-affinity cyclic configurations can be formed by an antigen, two capture monoclonal antibodies, and the surface of the solid phase.  (+info)

Fix L, a haemoglobin that acts as an oxygen sensor: signalling mechanism and structural basis of its homology with PAS domains. (51/1729)

Fix L, which contains a haemoglobin domain homologous to the PAS family and a histidine kinase domain, forms, with Fix J, a two-component signalling complex that regulates expression of nitrogenase genes in Rhizobium. Spin transitions of its haem iron trigger stereochemical changes in and around the haem that, together with steric effects, control the activity of the kinase. Homology with the PAS family is based on a common core of about 20 structurally equivalent sites from which polar residues are excluded.  (+info)

Troponin-I, myoglobin, and mass concentration of creatine kinase-MB in acute myocardial infarction. (52/1729)

Myoglobin, creatine kinase-MB (CKMB) mass concentration and troponin-I are newer biochemical markers for the diagnosis of acute myocardial infarction (AMI). We conducted a prospective study to formulate a model for the collective interpretation of these three markers in the diagnosis of AMI. Eighty-seven patients with AMI had serial serum samples taken to establish the time-frame sensitivity of individual markers. None of the markers had a good sensitivity within the first 4 h of infarction. Myoglobin and CKMB (mass) had sensitivities of 92.3% and 96.2%, respectively, at 4-8 h post infarct. CKMB (mass) and troponin-I had sensitivities >92% at 8-24 h. Troponin-I maintained sensitivity >93% until 72 h. A guideline was formulated based on the results. Our data suggest that troponin-I, myoglobin and CKMB (mass) yield satisfactory diagnostic sensitivity when used with reference to specific time frames. The combined use of these markers can provide valuable information for clinicians in managing AMI patients.  (+info)

Vibrational population relaxation of carbon monoxide in the heme pocket of photolyzed carbonmonoxy myoglobin: comparison of time-resolved mid-IR absorbance experiments and molecular dynamics simulations. (53/1729)

The vibrational energy relaxation of carbon monoxide in the heme pocket of sperm whale myoglobin was studied by using molecular dynamics simulation and normal mode analysis methods. Molecular dynamics trajectories of solvated myoglobin were run at 300 K for both the delta- and epsilon-tautomers of the distal His-64. Vibrational population relaxation times of 335 +/- 115 ps for the delta-tautomer and 640 +/- 185 ps for the epsilon-tautomer were estimated by using the Landau-Teller model. Normal mode analysis was used to identify those protein residues that act as the primary "doorway" modes in the vibrational relaxation of the oscillator. Although the CO relaxation rates in both the epsilon- and delta-tautomers are similar in magnitude, the simulations predict that the vibrational relaxation of the CO is faster in the delta-tautomer with the distal His playing an important role in the energy relaxation mechanism. Time-resolved mid-IR absorbance measurements were performed on photolyzed carbonmonoxy hemoglobin (Hb(13)CO). From these measurements, a T(1) time of 600 +/- 150 ps was determined. The simulation and experimental estimates are compared and discussed.  (+info)

Skeletal muscle involvement in falciparum malaria: biochemical and ultrastructural study. (54/1729)

Biochemical evidence of skeletal muscle damage is common in malaria, but rhabdomyolysis appears to be rare. To investigate the relationship between serum creatine kinase and myoglobin levels, muscle histology, and renal function in Plasmodium falciparum infections, we studied 13 patients with uncomplicated malaria, 13 with severe noncerebral malaria, and 10 with cerebral malaria. A muscle biopsy specimen was obtained from each patient for light microscopy and electron microscopy. Mean serum creatine kinase concentrations +/- SD were raised but similar for the three groups (258 +/- 277, 149 +/- 158, and 203 +/- 197 U/L, respectively; P = .5). The mean serum myoglobin level +/- SD was highest in cerebral malaria (457 +/- 246 vs. 170 +/- 150 and 209 +/- 125 ng/mL in uncomplicated and severe malaria, respectively; P < .01) and correlated with the mean serum creatinine level (r = .39 for 36 patients; P = .02). The number of intravascular parasites, proportion of mature forms, and glycogen depletion were highest in biopsy specimens from patients with cerebral malaria. Myonecrosis was not observed. Muscle appears to be an important site for P. falciparum sequestration, which could contribute to metabolic and renal complications.  (+info)

Human VEGF gene expression in skeletal muscle: effect of acute normoxic and hypoxic exercise. (55/1729)

Vascular endothelial growth factor (VEGF) is involved in extracellular matrix changes and endothelial cell proliferation, both of which are precursors to new capillary growth. Angiogenesis is a vital adaptation to exercise training, and the exercise-induced reduction in intracellular PO2 has been proposed as a stimulus for this process. Thus we studied muscle cell PO2 [myoglobin PO2 (MbPO2)] during exercise in normoxia and in hypoxia (12% O2) and studied the mRNA levels of VEGF in six untrained subjects after a single bout of exercise by quantitative Northern analysis. Single-leg knee extension provided the acute exercise stimulus: a maximal test followed by 30 min at 50% of the peak work rate achieved in this graded test. Because peak work rate was not affected by hypoxia, the absolute and relative work rates were identical in hypoxia and normoxia. Three pericutaneous needle biopsies were collected from the vastus lateralis muscle, one at rest and then the others at 1 h after exercise in normoxia or hypoxia. At rest (control), VEGF mRNA levels were very low (0.38 +/- 0.04 VEGF/18S). After exercise in normoxia or hypoxia, VEGF mRNA levels were much greater (16.9 +/- 6.7 or 7.1 +/- 1.8 VEGF/18S, respectively). In contrast, there was no measurable basic fibroblast growth factor mRNA response to exercise at this 1-h postexercise time point. Magnetic resonance spectroscopy of myoglobin confirmed a reduction in MbPO2 in hypoxia (3.8 +/- 0.3 mmHg) compared with normoxia (7.2 +/- 0.6 mmHg) but failed to reveal a relationship between MbPO2 during exercise and VEGF expression. This VEGF mRNA increase in response to acute exercise supports the concept that VEGF is involved in exercise-induced skeletal muscle angiogenesis but questions the importance of a reduced cellular PO2 as a stimulus for this response.  (+info)

Compatibility of osmolytes with Gibbs energy of stabilization of proteins. (56/1729)

This study led to the conclusion that naturally occurring osmolytes which are known to protect proteins against denaturing stresses, do not perturb the Gibbs energy of stabilization of proteins at 25 degrees C (DeltaG(D) degrees ) which has been shown to control the in vivo rate of degradative protein turnover (Pace et al., Acta Biol. Med. Germ 40 (1981) 1385-1392). This conclusion has been reached from our studies of heat-induced denaturation of lysozyme, ribonuclease A, cytochrome c and myoglobin in the presence of different concentrations of osmolytes, namely, glycine, proline, sarcosine and glycine-betaine. At a fixed concentration of osmolyte a heat-induced denaturation curve measured by following changes in the molar absorption coefficient of the protein, was analyzed for T(m), the midpoint of the denaturation and DeltaH(m), the enthalpy change of denaturation at T(m). Values of DeltaG(D) degrees were determined with Gibbs-Helmoltz equation using known values of T(m), DeltaH(m) and DeltaC(p), the constant-pressure heat capacity change. It has been observed that T(m) increases with the osmolyte concentration, whereas DeltaG(D) degrees remains unaffected in the presence of the osmolyte. This observation on DeltaG(D) degrees in the presence of osmolytes has been considered in the physiological context.  (+info)