Question

2. Myoglobin (Mb) is one of the most thoroughly studied and best understood proteins. It serves as a model for ligand binding by proteins. Mb is an example of a hemoprotein (a heme containing protein or heme protein) and its ligand is molecular oxygen (O2) which is essential for the survival of aerobic organisms. a. How does an organism benefit from having a protein bind O2? b. Where, specifically, does the ligand bind in Mb? c. Is the heme bound to Mb covalently or non-covalently? (check one) Covalently Non-covalently d. Conjugated proteins are those that require prosthetic groups. The term apoprotein is used to refer to a conjugated protein that does not have its prosthetic group. Based on this description, what is apomyoglobin? (Be specific in your answer) e. Can apomyoglobin bind O2? (as a group, check one and provide a short explanation for your answer) Yes No Maybe f. Given the function of Mb, and how O2 interacts with heme, provide at least two benefits of having the heme associated with a polypeptide as opposed to having free heme bind the ligand.

Answer 1

( a) The binding of Oz to myoglobin is a simple equibrium reaction :-) Mb + O₂ → MbO₂ Each myoglobin moleute is capable of binding one Oxygen, because myoglobin contains one heme per molecule. Even though the reaction of myoglobin and exygen takes place in solution, it is convenient to measure the concentreation of oxygen in terms of its partial pressure, the amount of gas in the atmospheue that is in equilbalum with the oxygen in solution. Myoglobin is an iron containing protein in muscle, neceives oxygen from RBC and transposts it to the mitochondria of muscle cells, where the oxygen is used in celcelar respication to produce energy Each myoglobin molecule has one heme prostretic groep located in hydrophobic cleft in protein . The binding of O₂ couses substantial stercultural change at the recenture, which shrinks in radius and moves into the centue of Ny pocket. O2- binding indues opin-paising" the five - Coordinate ferrous deoxy from is high spin and the six coordinate oxy form is low spin and diamagnetic. Many models of myogloben have been synthesived as a fast of broad interest in transition metal dioxygen complexes. I well known example is picket ferme porphyun, which consist of

a fewrous complex of sterically becky derivative of terraphenyl posperpen. In the presence of an imidazole elgand, this ferous complex reversibly binds 02. The O₂ suostecate adopts a bent geometry, Occupying the sixth position of iron centue a R loro fe ofeo N 190S ме. A picket tence porpergaun complex of re, with axial coordination sites occupied by methylimo da sole gueen) and dioxygen The R geroeps flank the O-binding site.

© No, apomyoglobin doesn't bind Oz. Apomyogloben i.e., heme free - myogeobor, is a small, alpha-helical protein that contains two righly conserved tryptophange residues located at positions 78 14 in N-terminal region of molecule. The folding of this protein fe known to proceed through compact intermediates. In most of these intermed- latce A G & H helices are tolded & sterically oriented as in the native AGH subdomain, where as the remainder of molecule ceems to be un ordened. The additional, secondary & fections Streeeteve modules are subsequently formed." Once folding has occurred, the heme binds to crevice formed essentially by & 8 f helices. Heme is bound to Nb covalently. NCS