Myoglobin oxygen binding


These calculations have shown that collective movements occur on the picosecond time scale for individual residues, and in nanoseconds for loop regions. Such movements are very important for the function of many protein molecules. Reactions such as electron transfer or ligand binding and release occur on these time scales and usually require movements of protein atoms. As soon as the structure of myoglobin was determined it was immediately apparent that the static picture of the myoglobin molecule seen in the crystal did not allow oxygen atoms to enter its binding site or diffuse out. We now know that while the myoglobin molecule is breathing, pathways are opened up between the solvent and the buried binding site to allow oxygen binding or release on a time scale of nanoseconds.  [c.105]

Hemoglobin is the oxygen-canying protein of blood. It binds oxygen at the lungs and transports it to the muscles, where it is stored by myoglobin. Hemoglobin binds oxygen in very much the same way as myoglobin, using heme as the prosthetic group. Hemoglobin is much larger than myoglobin, however, having a molecular weight of 64,500, whereas that of myoglobin is 17,500 hemoglobin contains four heme units, myoglobin only one. Hemoglobin is an assembly of four hemes and four protein chains, including two identical chains called the alpha chains and two identical chains called the beta chains.  [c.1148]

Mb Sperm whale myoglobin, an oxygen-binding protein 153 amino acid residues. Note that Mb lacks cysteine.  [c.114]

Before examining myoglobin and hemoglobin in detail, let us first encapsulate the lesson Myoglobin is a compact globular protein composed of a single polypeptide chain 153 amino acids in length its molecular mass is 17.2 kD (Figure 15.23). It contains heme, a porphyrin ring system complexing an iron ion, as its prosthetic group (see Figure 5.15). Oxygen binds to Mb via its heme. Hemoglobin (Hb) is also a compact globular protein, but Hb is a tetramer. It consists of four polypeptide chains, each of which is very similar structurally  [c.480]

The oxygen-binding equations for myoglobin and hemoglobin are described in detail in the Appendix at the end of this chapter. The relative oxygen affinities of hemoglobin and myoglobin reflect their respective physiological roles (see Figure 15.22). Myoglobin, as an oxygen storage protein, has a greater affinity for Og than hemoglobin at all oxygen pressures. Hemoglobin, as the oxygen carrier, becomes saturated with Og in the lungs, where the partial pressure of Og (pO ) is about 100 torr. In the capillaries of tissues, pO is typically 40 torr, and oxygen is released from Hb. In muscle, some of it can be bound by myoglobin, to be stored for use in times of severe oxygen deprivation, such as during strenuous exercise.  [c.483]

The Oxygen-Binding Curves of Myoglobin and Hemoglobin  [c.495]

The value Pso has been defined above for myoglobin as the pO that gives 50% saturation of the oxygen-binding protein with oxygen. Noting that at 50% saturation, F= (1 — F), then we have from Equation (A15.13).  [c.498]

Some substances such as CO form strong bonds to the iron of heme strong enough to displace O2 from it Carbon monoxide binds 30-50 times more effectively than oxygen to myoglobin and hundreds of times better than oxygen to hemoglobin Strong binding of CO at the active site interferes with the ability of heme to perform its biological task of transporting and storing oxygen with potentially lethal results  [c.1150]

Some substances, such as CO, fonn strong bonds to the iron of heme, strong enough to displace O2 from it. Carbon monoxide binds 30-50 times more effectively than oxygen to myoglobin and hundreds of times better than oxygen to hemoglobin. Strong binding of CO at the active site interferes with the ability of heme to perfonn its biological task of transporting and storing oxygen, with potentially lethal results.  [c.1150]

A comparison of the properties of hemoglobin and myoglobin offers insights into allosteric phenomena, even though these proteins are not enzymes. Hemoglobin displays sigmoid-shaped Og-binding curves (Figure 15.22). The unusual shape of these curves was once a great enigma in biochemistry. Such curves closely resemble allosteric enzyme substrate saturation graphs (see Figure 15.8). In contrast, myoglobin s interaction with oxygen obeys classical Michaelis-Menten-type substrate saturation behavior.  [c.480]

FIGURE 15.26 Oxygen and carbon monoxide binding to the heme group of myoglobin.  [c.482]

The reversible binding of oxygen to myoglobin,  [c.495]

Hemoglobin is the oxygen carrying protein of blood It binds oxygen at the lungs and transports it to the muscles where it is stored by myoglobin Hemoglobin binds oxy gen m very much the same way as myoglobin using heme as the prosthetic group Hemoglobin is much larger than myoglobin however having a molecular weight of 64 500 whereas that of myoglobin is 17 500 hemoglobin contains four heme units myo globm only one Hemoglobin is an assembly of four hemes and four protein chains including two identical chains called the alpha chains and two identical chains called the beta chains  [c.1148]

The oxygen-binding heme protein of muscle, myoglobin, consists of a single polypeptide chain of 153 residues. Hemoglobin, the oxygen transport protein of erythrocytes, is a tetramer composed of two a-chalns (141 residues each) and two /3-chalns (146 residues each). These globin polypeptides—myoglobin, a-globin, and /3-globin—share a strong degree of sequence homology (Figure 5.30). Human myoglobin and the human a-globin chain show 38 amino acid  [c.146]

Iron ions, whether ferrous or ferric, prefer to interact with six ligands, four of which share a common plane. The fifth and sixth ligands lie above and below this plane (see Figure 15.25). In heme, four of the ligands are provided by the nitrogen atoms of the four pyrroles. A fifth ligand is donated by the imidazole side chain of amino acid residue His F8. When myoglobin binds Og to become oxymyoglobin, the Og molecule adds to the heme iron ion as the sixth ligand (Figure 15.25). Og adds end on to the heme iron, but it is not oriented perpendicular to the plane of the heme. Rather, it is tilted about 60° with respect to the perpendicular. In deoxymyoglobin, the sixth ligand position is vacant, and in metmyoglobin, a water molecule fills the Og site and becomes the sixth ligand for the ferric atom. On the oxygen-binding side of the heme lies another histidine residue. His E7. While its imidazole function lies too far away to interact with the Fe atom, it is close enough to contact the Og. Therefore, the Og-binding site is a sterically hindered region. Biologically important properties stem from this hindrance. For example, the affinity of free heme in solution for carbon monoxide (CO) is 25,000 times greater than its affinity for Og. But CO only binds 250 times more tightly than Og to the heme of myoglobin, because His E7 forces the CO molecule to tilt away from a preferred perpendicular alignment with the plane of the heme (Figure 15.26). This diminished affinity of myoglobin for CO guards against the possibility that traces of CO produced during metabolism might occupy all of the heme sites, effectively preventing Og from binding. Nevertheless, CO is a potent poison and can cause death by asphyxiation.  [c.482]

Iron(II) porphyrins react rapidly with O2 to afford p.-oxo-btidged complexes [Fe(III)Por]20 where For is porphyrin. Antiferromagnetic coupling of the two high spin iron atoms reduces the room temperature magnetic moment to about 1.7 x 10 J/T (1.8 /tg /Fe). The reaction involves coordination of O2 to the heme followed by reaction of another equivalent of heme to afford a p.-peroxy-bridged [Fe(III)Por]202 intermediate, homolysis to afford two equivalents of an 0x0 iron(IV) intermediate, and reaction with yet another equivalent of heme to yield the p.-oxo product. Reversible binding of dioxygen, O2, to the heme can occur if steric encumberance of the O2 binding site prevents the approach of a second heme. This is the basis of the success of synthetic O2 binding complexes like picket fence porphyrins. Clearly, one function of the protein surrounding the heme site in the biological oxygen carriers myoglobin and hemoglobin is to isolate the oxygen and prevent its irreversible oxidation. A second function in hemoglobin is to mediate cooperative binding of O2 by the four heme sites in each molecule. The movement of the iron atom with respect to the porphyrin plane upon O2 binding is thought to play an important role in cooperativity.  [c.441]

The hemoglobin molecule (mol wt 65,000) is a tetramer containing four iron atoms (77). The iron reversibly binds oxygen, allowing the hemoglobin molecule to function as an oxygen carrier to the tissues (78). Myoglobin, a monomer containing one iron atom, functions accepting oxygen from the blood and storing it for use during muscle contraction. The iron in both hemoglobin and myoglobin is in the ferrous state, Fe ". The iron in methemoglobin and metmyoglobin is oxidized to the ferric state, Fe ". These latter species do not bind oxygen (77).  [c.384]

Ancient life forms evolved in the absence of oxygen and were capable only of anaerobic metabolism. As the earth s atmosphere changed over time, so too did living things. Indeed, the production of Og by photosynthesis was a major factor in altering the atmosphere. Evolution to an oxygen-based metabolism was highly beneficial. Aerobic metabolism of sugars, for example, yields far more energy than corresponding anaerobic processes. Two important oxygenbinding proteins appeared in the course of evolution so that aerobic metabolic processes were no longer limited by the solubility of Og in water. These proteins are represented in animals as hemoglobin (Hb) in blood and myoglobin (Mb) in muscle. Because hemoglobin and myoglobin are two of the most-studied proteins in nature, they have become paradigms of protein structure and function. Moreover, hemoglobin is a model for protein quaternary structure and allosteric function. The binding of Og by hemoglobin, and its modulation by effectors such as protons, COg, and 2,3-bisphosphoglycerate, depend on interactions between subunits in the Hb tetramer. Subunit-subunit interactions in Hb reveal much about the functional significance of quaternary associations and allosteric regulation.  [c.480]

What happens when the heme group of myoglobin binds oxygen X-ray crystallography has revealed that a crucial change occurs in the position of the iron atom relative to the plane of the heme. In deoxymyoglobin, the ferrous ion has but five ligands, and it lies 0.055 nm above the plane of the heme, in the direction of HisF8. The iron porphyrin complex is therefore dome-shaped.  [c.482]


See pages that mention the term Myoglobin oxygen binding : [c.1148]    [c.283]    [c.1148]    [c.481]   
Introduction to protein structure (1999) -- [ c.105 ]