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handout5_blank - Structural Biochemistry TA Phu Tran...

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Structural Biochemistry Dr. Lukas Buehler TA Phu Tran pdtran@ucsd.edu Sections A03 W 1 - 3 pm Solis 111 OH Monday after class Handout 7 Myoglobin, Hemoglobin Myoglobin is a protein in heart and skeletal muscles. It acts as an extra endogenous reserve of oxygen. It has higher affinity for O 2 than Hemoglobin, so it can receive O 2 from circulating hemoglobin. The pO 2 of arterial blood is about 100mmHg or 100 Torr. The pO 2 of venous blood is about 40mmHg. Myoglobin is composed of _ ________ _ subunit, whereas Hemoglobin is composed of _ ________ _ subunits (αβ) 1 ( αβ) 2 . The α 1 β 1 dimer and α 2 β 2 dimer interface with each other at the α 1 2 and α 2 1 interfaces, which are noncovalent hydrogen bonds. Hemoglobin is tetrameric and α-helical. It binds to up to 4 oxygens and is much more prevalent in blood. It also has heme groups. After binding to a single oxygen molecule, hemoglobin undergoes a _ ________ _ change, tilting the axis (quarternary structure) of the α 2 β 2 dimer relative to the α 1 β 1 dimer and gains an _ ________ _ in affinity for binding additional oxygens. The heme group is made of a porphyrin ring and an attached Fe 2+ ion (covalently and hydrogen bonded to the heterocyclic ring). The iron ion is stabilized by a Histidine of the F8 helix on one side and binds to O 2 on the other side. The heme group is also stabilized by Val/Phe hydrophobic interactions above and below the ring. In the _ _ _ (tense/deoxy) state, the heme group is not bound to a ligand. In the _ _ _ (relaxed/oxygenated) state, the heme group is bound to an O 2 molecule. At pO 2 in arterial blood or at the lungs, Hb and Myoglobin both have similar affinity for oxygen. However, in venous blood and pO 2 of actively metabolizing tissues, Myoglobin has a higher affinity for oxygen and thus takes oxygen from Hemoglobin. The P50 (K
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handout5_blank - Structural Biochemistry TA Phu Tran...

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