Showing papers on "Myoglobin published in 1995"
TL;DR: Large differences in PO2 between blood and intracellular tissue have been demonstrated in intact normal human muscle and are found over a wide range of exercise intensities, consistent with an O2 diffusion limitation across the 1-5-microns path-length from red cell to the sarcolemma that plays a role in determining maximal muscle O2 uptake in normal humans.
Abstract: The assumption that cellular oxygen pressure (PO2) is close to zero in maximally exercising muscle is essential for the hypothesis that O2 transport between blood and mitochondria has a finite conductance that determines maximum O2 consumption. The unique combination of isolated human quadriceps exercise, direct measures of arterial, femoral venous PO2, and 1H nuclear magnetic resonance spectroscopy to detect myoglobin desaturation enabled this assumption to be tested in six trained men while breathing room air (normoxic, N) and 12% O2 (hypoxic, H). Within 20 s of exercise onset partial myoglobin desaturation was evident even at 50% of maximum O2 consumption, was significantly greater in H than N, and was then constant at an average of 51 +/- 3% (N) and 60 +/- 3% (H) throughout the incremental exercise protocol to maximum work rate. Assuming a myoglobin PO2 where 50% of myoglobin binding sites are bound with O2 of 3.2 mmHg, myoglobin-associated PO2 averaged 3.1 +/- .3 (N) and 2.1 +/- .2 mmHg (H). At maximal exercise, measurements of arterial PO2 (115 +/- 4 [N] and 46 +/- 1 mmHg [H]) and femoral venous PO2 (22 +/- 1.6 [N] and 17 +/- 1.3 mmHg [H]) resulted in calculated mean capillary PO2 values of 38 +/- 2 (N) and 30 +/- 2 mmHg(H). Thus, for the first time, large differences in PO2 between blood and intracellular tissue have been demonstrated in intact normal human muscle and are found over a wide range of exercise intensities. These data are consistent with an O2 diffusion limitation across the 1-5-microns path-length from red cell to the sarcolemma that plays a role in determining maximal muscle O2 uptake in normal humans.
617 citations
TL;DR: For ruling out AMI in the emergency room, myoglobin is a better marker than CK-MBmass or troponin T from 3 until 6 hours after the onset of symptoms, but the maximal NPV reaches only 89%.
Abstract: Background Ruling out acute myocardial infarction (AMI) on the basis of rapid assays for cardiac markers will allow early triage of patients and cost-effective use of available coronary care facilities. Methods and Results We studied the value of myoglobin, creatine kinase (CK)–MBmass, and troponin T in ruling out an AMI in the emergency room in 309 consecutive patients presenting with chest pain. The gold standard for AMI was the combination of history, ECG, and a typical curve of the CK-MB activity (CK-MBact). Myoglobin was the earliest marker, and its negative predictive value (NPV) was significantly higher than for CK-MBmass and troponin T from 3 to 6 hours after the onset of symptoms (myoglobin versus CK-MBmass, P<.03; myoglobin versus troponin T, P<.01). The NPV of myoglobin reached 89% 4 hours after the onset of symptoms. The NPV of CK-MBmass reached 95% 7 hours after the onset of symptoms. Troponin T was not an early marker for ruling out AMI, and NPV changed over time, together with CK-MBact. The...
312 citations
TL;DR: These results help to establish how myoglobin discriminates against CO, a controversial issuedominated by the misconception that Fe-C-O is bent.
Abstract: The relative orientations of carbon monoxide (CO) bound to and photodissociated from myoglobin in solution have been determined with time-resolved infrared polarization spectroscopy. The bound CO is oriented < or = 7 degrees from the heme normal, corresponding to nearly linear FE-C-O. Upon dissociation from the Fe, CO becomes trapped in a docking site that orientationally constrains it to lie approximately in the plane of the heme. Because the bound and "docked" CO are oriented in nearly orthogonal directions CO binding from the docking site is suppressed. These solutions results help to establish how myoglobin discriminates against CO, a controversial issue dominated by the misconception that Fe-C-O is bent.
261 citations
TL;DR: The ratio of the concentrations of myoglobin over FABP in plasma from patients with muscle injury reflects the ratio found in the affected tissue, which allows the discrimination between myocardial and skeletal muscle injury in humans.
Abstract: Background Myoglobin and fatty acid–binding protein (FABP) each are useful as early biochemical markers of muscle injury. We studied whether the ratio of myoglobin over FABP in plasma can be used to distinguish myocardial from skeletal muscle injury. Methods and Results Myoglobin and FABP were assayed immunochemically in tissue samples of human heart and skeletal muscle and in serial plasma samples from 22 patients with acute myocardial infarction (AMI), from 9 patients undergoing aortic surgery (causing injury of skeletal muscles), and from 10 patients undergoing cardiac surgery. In human heart tissue, the myoglobin/FABP ratio was 4.5 and in skeletal muscles varied from 21 to 73. After AMI, the plasma concentrations of both proteins were elevated between ≈1 and 15 to 20 hours after the onset of symptoms. In this period, the myoglobin/FABP ratio was constant both in subgroups of patients receiving and those not receiving thrombolytics and amounted to 5.3±1.2 (SD). In serum from aortic surgery patients, bo...
221 citations
TL;DR: High-resolution structures of the aquomet, deoxy, and CO forms of Ala68, Ile68, Leu68, and Phe68 sperm whale myoglobins have been determined by X-ray crystallography, and these 12 new structures have been used to interpret the effects of mutations at position 68 and theeffects of cobalt substitution on the kinetics of O2, CO, and NO binding.
184 citations
TL;DR: The residues circumscribing the heme pocket in hemoglobin and myoglobin fashion a cavity near the binding site that accommodates the dissociated CO and restricts its rotational motion, which may be important to the function of ligand‐binding heme proteins.
Abstract: Time‐resolved mid‐ir absorption spectra of CO at 283 K have been measured 100 ps after photodissociation from human hemoglobin A, horse myoglobin, and sperm whale myoglobin. The spectra reveal two vibrational features that are narrower than any reported for CO in the condensed phase near room temperature, indicating that CO becomes localized in a rotationally constrained environment. The integrated absorbance under these narrow features is 0.53±0.05 times that found for sperm whale myoglobin in low temperature glasses. A model is developed that relates this reduction of integrated absorbance to molecular motion in a rotationally constrained environment. From this model, the barrier to CO rotation is found to be 1.5±0.25 kcal/mol. The two vibrational features are tentatively assigned to CO oriented oppositely in the same site within the heme pocket. Evidently, the residues circumscribing the heme pocket in hemoglobin and myoglobin fashion a cavity near the binding site that accommodates the dissociated CO and restricts its rotational motion. This ‘‘docking’’ site mediates ligand transport to and from the active binding site and may be important to the function of ligand‐binding heme proteins.
131 citations
TL;DR: Analysis of the structure of D1 reveals a characteristic globin fold and illuminates molecular features involved in oxygen avidity of Ascaris perienteric hemoglobin.
Abstract: The perienteric hemoglobin of the parasitic nematode Ascaris has an exceptionally high affinity for oxygen. It is an octameric protein containing two similar heme-binding domains per subunit, but recombinant constructs expressing a single, monomeric heme-binding domain (domain 1; D1) retain full oxygen avidity. We have solved the crystal structure of D1 at 2.2 A resolution. Analysis of the structure reveals a characteristic globin fold and illuminates molecular features involved in oxygen avidity of Ascaris perienteric hemoglobin. A strong hydrogen bond between tyrosine at position 10 in the B helix (tyrosine-B10) and the distal oxygen of the ligand, combined with a weak hydrogen bond between glutamine-E7 and the proximal oxygen, grips the ligand in the binding pocket. A third hydrogen bond between these two amino acids appears to stabilize the structure. The B helix of D1 is displaced laterally by 2.5 A when compared with sperm whale myoglobin. This shifts the tyrosine-B10 hydroxyl far enough from liganded oxygen to form a strong hydrogen bond without steric hindrance. Changes in the F helix compared with myoglobin contribute to a tilted heme that may also be important for oxygen affinity.
115 citations
Journal Article•
TL;DR: The authors' observed biochemical alterations suggest that the energy-producing proteins CK-MB and myoglobin are upregulated following cellular damage, while the structural and regulatory protein cTnT does not have a mechanism for replacement of lost protein following cell injury and necrosis.
Abstract: Objective. ― Cardiac troponin T (cTnT) has been suggested as a new, more specific marker of myocardial cellular damage. The objectives of this study were to examine the distribution of cTnT and creatine kinase (CK)-MB in normal and diseased heart tissue of dogs and humans, and to assess the use of serum cTnT for the estimation of infarct size in dogs. Design. ― Serial serum specimens over 7 days were obtained from normal dogs (controls, n = 3) and dogs that underwent surgical coronary artery occlusion (n = 6). Heart muscle samples were obtained from the controls and after 3 weeks of occlusion in experimental dogs. Diseased human heart muscle samples were obtained at autopsy from patients who had died of acute myocardial infarction (n = 3). Normal heart muscle samples (n = 3) were obtained at autopsy from patients who died of non-cardiac-related illnesses. Tissues were sectioned and homogenized to harvest both cytosolic and myofibril-bound proteins. Serum samples and tissue homogenates were assayed for cTnT, CK-MB, and myoglobin (humans only). Total protein was assayed on homogenate samples and results were reported as milligrams per gram of total protein. Results. ― The distributions of cTnT, CK-MB, and myoglobin were equivalent across 14 sites within normal human heart. Creatine kinase-MB and myoglobin were more than 99% cytosolic. Cardiac troponin T was 92% myofibril bound and 8% cytosolic. In the control dog hearts, cTnT was higher and CK-MB was lower in the right ventricle than in the left ventricle. While CK-MB and myoglobin were more than 99% cytosolic, cTnT was 98% myofibril bound and 2% cytosolic. Infarct sizing in dog hearts initially did not correlate well with serum cTnT or CK-MB concentrations. However, when the data were separated by infarct location (right coronary artery; left circumflex coronary artery), the correlations improved dramatically. Differences in tissue concentrations of cTnT and CK-MB between the left and right ventricle might explain the change in correlations. Coronary artery occlusion in dogs and humans resulted in decreased cytosolic and myofibril cTnT and increased CK-MB and myoglobin in diseased myocardial tissue. Conclusions. ― Our observed biochemical alterations suggest that the energy-producing proteins CK-MB and myoglobin are upregulated following cellular damage, while the structural and regulatory protein cTnT does not have a mechanism for replacement of lost protein following cell injury and necrosis.
110 citations
TL;DR: The results establish that heme doming occurs as an ultrafast reaction to ligand dissociation and that he me doming is the primary event in the sequence of conformational changes leading to the cooperative R-->T transition.
Abstract: Separation of the photophysical aspects of the sub-picosecond (sub-ps) time-resolved resonance Raman signal from contributions due to conformation has been achieved by comparing deoxyhemoglobin (Hb) in the T state with (carbonmonoxy)hemoglobin (HbCO), deoxy-P4 @CO) (all R state), and monomers deoxymyoglobin and (carbonmonoxy)myoglobin (MbCO) 104 consists of a tetramer of four P-subunits and shows no cooperativity). In all photolyzed species, Hb*(CO), Mb*(CO), and P4*(CO), the iron- histidine out-of-plane mode (YFe-His), indicative of heme doming, achieves 90% of its full intensity in 1 ps. The frequency of this mode (223-228 cm-') is shifted significantly relative to equilibrium deoxy- Hb (210-216 cm-') in the T state, but not with respect to either equilibrium deoxy-Mb or deoxy-/34. A correlation between the +12 cm-' bandshift of VFe-His and the -2 cm-' shift of the electron density marker band (~4 at 1370 cm-l) relative to T-state deoxy-Hb is shown to hold on all time scales, including the sub-picosecond time scale. Photolyzed Hb*(CO) consists of R-state or weakly interacting tetramers on the picosecond time scale and is shown to have properties similar to those of photolyzed Mb*(CO) and /34*(CO> on the picosecond time scale. These results establish that heme doming occurs as an ultrafast reaction to ligand dissociation and that heme doming is the primary event in the sequence of conformational changes leading to the cooperative R - T transition. In the oxygen transport protein hemoglobin, the formation or breakage of a single chemical bond between the heme iron and a diatomic ligand is transmitted to the protein and expressed in terms of intersubunit structural changes, which ultimately modify the binding affinity of all four heme irons in the protein. The X-ray crystal structure of hemoglobin shows that the heme iron is nearly coplanar with the heme in ligated hemoglobin and more than 0.4 A from the heme
104 citations
81 citations
TL;DR: The result that these helices are the most stable suggest that the intrinsically more stable helices form early in the folding process and that this significantly influences the folding pathway of apomyoglobin.
Abstract: The apo form of myoglobin has two non-native stable states that have been experimentally characterized. Investigation of these states has suggested possible folding pathways for myoglobin. We have performed molecular dynamics simulations on solvated isolated helices of myoglobin to investigate the relationship between the intrinsic stabilities of the isolated helices and the structure and folding pathway of apomyoglobin. Analyses of hydrogen bonding and fluctuations from simulations at 298 and 368 K are used to explore the relative stabilities of the helices of myoglobin. The ordering observed is A approximately G approximately H > B > E > F, which mirrors both the experimental equilibrium and kinetic data available for apomyoglobin. The experimental observation that a subdomain comprising helices A, G, and H is an important early intermediate and our result that these helices are the most stable suggest that the intrinsically more stable helices form early in the folding process and that this significantly influences the folding pathway.
TL;DR: The only feature capable of accounting for the high on-rate of the reaction with oxygen are the mobilities of the proximal histidine and distal histidine residues in deoxy-leghaemoglobin and the oscillation of the imidazole between the two orientations.
TL;DR: The distribution of HH-FABPc in the heart and skeletal muscles was comparable to that of cardiac-specific creatine kinase (CK-MB) activity, and was inverse to the distribution of myoglobin.
Abstract: Human heart-type cytoplasmic fatty acid-binding protein (HH-FABPc) has been proposed as an early biochemical indicator of acute myocardial infarction (AMI). However, skeletal muscles also contain HH-FABPc identical to that found in the heart. Before HH-FABPc can be clinically employed as an indicator of AMI, its content in various tissues other than the heart must be known. Accordingly, we measured the HH-FABPc content of various human muscles and organs, using a sandwich enzyme-linked immunosorbent assay (ELISA) for HH-FABPc. HH-FABPc was abundant in the ventricles (0.46 mg/g wet weight and 1.5% of the cytoplasmic protein in the left ventricle), while the atria contained slightly less HH-FABPc (0.25 mg/g wet weight and 0.7% of the cytoplasmic protein in the left atrium). Of the skeletal muscles tested, the diaphragm contained about one-quarter of the HH-FABPc content of the heart, but other skeletal muscles contained very low levels of this protein. Other than the muscles, the kidneys contained less than one-tenth of the HH-FABPc in the heart, and negligible amounts were found in the liver and small intestine. The distribution of HH-FABPc in the heart and skeletal muscles was comparable to that of cardiac-specific creatine kinase (CK-MB) activity, and was inverse to the distribution of myoglobin. The plasma myoglobin/HH-FABPc ratio, determined in patients with AMI and those without AMI, closely reflected that in the heart and skeletal muscles. These findings indicate that HH-FABPc may be useful as a specific indicator of AMI, and the plasma myoglobin/HH-FABPc ratio could provide valuable information for the diagnosis of AMI.
TL;DR: The sequential nature of the cellular response to limiting O2, starting with alterations in the lactate formation rate and RPP, indicates that NADH, rather than ADP, signals tissue hypoxia.
Abstract: The 1H nuclear magnetic resonance (NMR) signal of tissue myoglobin has provided an opportunity to determine the critical O2 level in saline-perfused myocardium at room temperature Above the intrac
TL;DR: Qin et al. as mentioned in this paper have shown that the three-dimensional positions of His64 and Val68 in the wild-type myoglobin are as important as the chemical nature of the side chains in facilitating reversible O2 binding and inhibiting autooxidation.
TL;DR: It is confirmed that a Phe residue is present at position 29 (B10) in elephant myoglobin, and not a Leu residue as is reported in the published amino acid sequence, and the single Gln64(E7) substitution lowers oxygen affinity ∼5-fold and increases the rate of autooxidation 3-fold.
TL;DR: Results suggest that, even though distal effects probably also play a role, proximal effects make an important contribution in modulating ligand-iron bond formation.
Abstract: In either sperm whale or horse heart myoglobin, binding of NO and lowering of solution pH work together to weaken, and ultimately break, the bond between iron and the proximal histidine. This is reminiscent of the reaction observed at neutral pH in the case of guanylate cyclase, the heme enzyme that catalyzes the conversion of GTP to cGMP. Bond breaking is characterized by a spectral change from a nine-line to a three-line ESR signal and accompanied by a shift from 420 to 387 nm in the UV-vis spectrum of the Soret band maximum. Analysis of the pH-dependent spectral changes shows that they are reversible, at least within a few hours, that the transition is cooperative, involving six protons during pH lowering but only two as it is raised, and that the pK is about 4.7. Different proteins exhibit different pK values, which are generally lower than that for "chelated" protoheme. The pK differences reflect the extra bond stability afforded by the protein structure. Investigations of thermal and photochemical NO displacement by CO suggest that the local pocket around the ligand, although significantly altered (according to circular dichroism investigations), nonetheless still imposes a barrier against the outward diffusion of ligand into the solvent. Nanosecond and picosecond flash photolysis shows that in proteins at low pH there is an extremely efficient geminate recombination of the ligand with the four-coordinated species through a single-exponential process. This occurs to a significantly larger extent than for the case of NO-"chelated" protoheme (where no distal barrier for ligand is present). At neutral pH, when the proximal histidine bond is intact, the geminate recombination for NO takes longer and displays multiexponential kinetics. Altogether, these results suggest that, even though distal effects probably also play a role, proximal effects make an important contribution in modulating ligand-iron bond formation.
TL;DR: It was possible to show that urea release of rebound hemoglobin from the polymer made in the presence of hemoglobin was less than for myoglobin bound to the same polymer and visa versa, again suggesting induced properties unique to the polymer prepared with the predetermined protein.
TL;DR: The experiments show that these proteins exhibit conformational fluctuations at temperatures as low as 2 K, and the temperature dependence of the structural relaxation of myoglobin follows a simple Arrhenius law.
Abstract: Optical methods were used to study the internal motions of myoglobin and cytochrome c. The experiments show that these proteins exhibit conformational fluctuations at temperatures as low as 2 K. The distribution of fluctuation rates can be measured in real time and turns out to be very sharp. The temperature dependence of the structural relaxation of myoglobin follows a simple Arrhenius law. The results are in agreement with existing models for protein dynamics.
TL;DR: This result showed that disruption of the native structure of Mb occurs following interaction with PDMS, and the change in the absorption spectrum may indicate loss of heme from the heme pocket of the adsorbed protein.
TL;DR: This study was carried out to evaluate the stability of the 89 bound water molecules that were observed in the neutron diffraction study of CO myoglobin and showed that only 4 water molecules are continously bound during the length of this simulation while the other solvent molecules exhibit considerable mobility.
Abstract: This study was carried out to evaluate the stability of the 89 bound water molecules that were observed in the neutron diffraction study of CO myoglobin. The myoglobin structure derived from the neutron analysis was used as the starting point in the molecular dynamics simulation using the software package CHARMM. After salvation of the protein, energy minimization and equilibration of the system, 50 pico seconds of Newtonian dynamics was performed. This data showed that only 4 water molecules are continously bound during the length of this simulation while the other solvent molecules exhibit considerable mobility and are breaking and reforming hydrogen bonds with the protein. At any instant during the simulation, 73 of the hydration sites observed in the neutron structure are occupied by water.
TL;DR: The spectroscopic and structural properties of the His93Tyr variant of horse heart myoglobin have been studied to assess the effects of replacing the proximal His residue of this protein with a tyrosyl residue as occurs in catalases from various sources.
Abstract: The spectroscopic and structural properties of the His93Tyr variant of horse heart myoglobin have been studied to assess the effects of replacing the proximal His residue of this protein with a tyrosyl residue as occurs in catalases from various sources. The variant in the ferric form exhibits electronic spectra that are independent of pH between pH 7 and 10, and it exhibits changes in absorption maxima and intensity that are consistent with a five-coordinate heme iron center at the active site. The EPR spectrum of the variant is that of a high-spin, rhombic system similar to that reported for bovine liver catalase. The 1D 1H-NMR spectrum of the variant confirms the five-coordinate nature of the heme iron center and exhibits a broad resonance at 112.5 ppm that is attributable to the meta protons of the phenolate ligand. This result indicates that the new Tyr ligand flips at a significant rate in this protein. The thermal stability of the Fe(III) derivative is unchanged from that of the wild-type protein (pH 8) while the midpoint reduction potential [-208 mV vs SHE (pH 8.0, 25 degrees C)] is about 250 mV lower. The three-dimensional structure of the variant determined by X-ray diffraction analysis confirms the five-coordinate nature of the heme iron center and establishes that the introduction of a proximal Tyr ligand is accommodated by a shift of the F helix (residues 88-99) in which this residue resides away from the heme pocket. Additional effects of this change are small shifts in the positions of Leu29, a heme propionate, and a heme vinyl group that are accompanied by altered hydrogen bonding interactions with the heme prosthetic group.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Model calculations show that with this relatively low DMb value, the intracellular oxygen supply can be improved only slightly, and the implication for the role of Mb in the facilitation of oxygen transport was examined.
Abstract: We measured the diffusion coefficient of myo- globin (DMb) inside mammalian skeletal muscle cells with a microinjection technique. A small bolus of horse Mb was injected into a single muscle fibre and the sub- sequent time-dependent changes of the Mb profiles along the fibre axis were measured with a microscope- photometer. For fibres of the rat soleus muscle at 22 ~ C, a DMb of 1.3"10 -7 cmZ/s was found, confirming a result obtained previously by us for rat diaphragm muscle with a photo-oxidation technique. In the extensor dig- itorum longus muscle of the rat, a higher value of 1.9 �9 10 -7 cm2/s was measured. Auxotonic muscle con- tractions did not change the apparent DMb. For the tem- perature range between 22 ~ C and 37 ~ C, a temperature coefficient, Q~0, of 1.5 was calculated. The implication of this result for the role of Mb in the facilitation of oxygen transport was examined. Model calculations show that with this relatively low DMb value, the intra- cellular oxygen supply can be improved only slightly.
TL;DR: These studies suggest that myoglobin has greater potential than the other markers examined in the detection of reperfusion after thrombolytic treatment.
Abstract: OBJECTIVE--To investigate and compare the clinical usefulness of serial measurements of five cardiac marker proteins, namely creatine kinase (CK), CK-MB mass, myoglobin, troponin T, and myosin light chain 1, in the early detection of reperfusion after thrombolytic treatment. METHOD--Serial blood samples were taken from 26 patients presenting with acute myocardial infarction. Concentrations of the five markers were assayed in each sample. Thrombolytic treatment was given to the patients who were divided into those who reperfused (n = 17, group A) and those who failed to reperfuse (n = 9, group B) on the basis of clinical signs and angiography within 24 h. RESULTS--The release profiles of CK, CK-MB mass, myoglobin, and troponin T for patients in group A differed from those of patients in group B. No difference was observed in the release profile of myosin light chain 1 between the two groups. The time to peak concentration of CK, CK-MB mass, myoglobin, and troponin T occurred significantly earlier in patients of group A than in those of group B, with myoglobin peaking earlier than the other markers. An index, defined as the ratio of the concentration of each marker immediately before and 2 h after the start of thrombolytic treatment, was calculated for each marker in groups A and B. The 2 h myoglobin and troponin T indices were significantly different between groups A and B. The diagnostic efficiency of the myoglobin index, however, was best at 85%. CONCLUSIONS--These studies suggest that myoglobin has greater potential than the other markers examined in the detection of reperfusion after thrombolytic treatment.
TL;DR: Comparison with other myoglobin structures in various ligated forms reveals an essentially unchanged tertiary structure in elephant myoglobin despite the two amino acid substitutions in the heme pocket.
TL;DR: Results show that this mutation in the second shell of amino acids around the distal pocket can influence ligand binding significantly and inhibit geminate recombination and can be correlated with molecular dynamics calculations.
Abstract: The role of Phe-46(CD4) in modulating the functional properties of sperm whale myoglobin was investigated by replacing this residue with Leu, Ile, Val, Ala, Trp, Tyr, and Glu. This highly conserved amino acid almost makes direct contact with the distal histidine and has been postulated to affect ligand binding. The overall association rate constants for CO, O2, and NO binding were little affected by decreasing the size of residue 46 step-wise from Phe to Leu to Val to Ala. In contrast, the rates of CO, O2, and NO dissociation increased 4-, 10-, and 25-fold, respectively, for the same series of mutants, causing large decreases in the affinity of myoglobin for all three diatomic gases. The rates of autooxidation at 37 degrees C, pH 7.0 increased dramatically from approximately 0.1-0.3 h-1 for wild-type, Tyr-46, and Trp-46 myoglobins to 1.5, 5.2, 4.9, and 5.0 h-1 for the Leu-46, Ile-46, Val-46 and Ala-46 mutants, respectively. Rates of NO and O2 geminate recombination were measured using 35 ps and 9 ns laser excitation pulses. Decreasing the size of residue 46 causes significant decreases in the extent of both picosecond and nanosecond rebinding processes. High resolution structures of Leu-46 and Val-46 metmyoglobins, Val-46 CO-myoglobin, and Val-46 deoxymyoglobin were determined by X-ray crystallography. When Phe-46 is replaced by Val, the loss of internal packing volume is compensated by (1) contraction of the CD corner toward the core of the protein, (2) movement of the E-helix toward the mutation site, (3) greater exposure of the distal pocket to intruding solvent molecules, and (4) large disorder in the position of the side chain of the distal histidine (His-64). In wild-type myoglobin, the van der Waals contact between C zeta of Phe-46 and C beta of His-64 appears to restrict rotation of the imidazole side chain. Insertion of Val at position 46 relieves this steric restriction, allowing the imidazole side chain to rotate about the C alpha - C beta bond toward the surface of the globin and about the C beta - C gamma bond toward the space previously occupied by the native Phe-46 side chain. This movement disrupts hydrogen bonding with bound ligands, causing significant decreases in affinity, and opens the distal pocket to solvent water molecules, causing marked increases in the rate of autooxidation.(ABSTRACT TRUNCATED AT 400 WORDS)
TL;DR: The clinical utility of cardiac-specific troponins as markers for the early detection of AMI and monitoring of reperfusion following thrombolytic therapy are shown.
TL;DR: The suggested role of the cysteinate proximal ligand of P-450 as a strong internal electron donor to promote O-O bond cleavage in the putative ferric-peroxide intermediate to generate the proposed ferryl-oxo “active oxygen” state of the reaction cycle is supported.
TL;DR: It is found that steady-state myoglobin deoxygenation is increased progressively (and reversibly) as oxygenation of the perfusing medium is decreased in both saline and red blood cell-perfused hearts at constant work output.