BMB 401 Lecture 10 - BMB 401 Lecture 10 Notes (((Angela-...

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Unformatted text preview: BMB 401 Lecture 10 Notes (((Angela- everything typed in italics is what I got from watching the lecture)))) Hemoglobin : Tetrameric protein In RBC Main fxn: O2 transport Hb monomers contain: Heme prosthetic groups that contain iron o *Heme group binds oxygen Globin polypeptide chain o Provides optimal environment for heme function Oxygen binds to Fe in center of heme group Heme group gives blood color: Heme oxygenated= RED; deoxygenated= BLUE Globin : 75% helix (8 helices) Adult Hb: 2 major subtypes of polypeptide chain: globin & globin o Contains 2 & 2 globin polypeptids chains SLIDE 7 & 8: Fxn: globin polypeptide gives good environment for heme to function Each heme group in hydrophobic pocket within globin chain Heme: Planar prosthetic group Purpose: oxygen binding Heme is a : Fe- containing porphyrin Porphyrin- ring structure that acts as prosthetic groups for major proteins 2 main components: 1. organic- protoporphyrin IX 2. inorganic: central iron ion: Ferric Fe3+ & Ferrous Fe2+ ( exists in 2 oxidation states) * majority of heme prosthetic group= NON POLAR* Protoporphyrin IX- tetrapyrolle ring ~ 4 pyrrole rings interconnected by methane bridges ~ Central iron is coordinated (held in place) by Ns of all 4 rings All 4 rings have methyl groups 2 have propionate side chains ( POLAR cuz of carboxylic functional groups)-Propionates face out of Oxygen binding cleft toward aqueous environment 2 have vinyl groups ( NON POLAR)-Non-polar vinyls face in toward the hydrophobic binding cleft ** 6 Coordination Sites: ** 1-4 at each pyrrole N 5 th at Proximal Histidine 6 th is the oxygen that binds to Fe SLIDE 13 shows: Propionate side chain barely peaks out of O2 binding cleft Only 2 polar residues in the binding cleft: both are Histidines Histidines important for proper oxygen binding: 1. Distal: gatekeeper O2 transport Bulky, hard to get in O2 cleft 2. Proximal : Fe coordination supplies 5 th coord. Site SLIDE 16: 2.2 A only 2.2 A between Histidine Nitrogen & Fe- Propionate part to Right- Vinyl part to Left Dioxygen & Superoxide Ion Upon binding dioxygen, an unpaired electron of oxygen oxidizes the ferrous iron to ferric iron and oxygen is reduced to superoxide This results in no net unpaired electrons; thus, a lower energy state Resonance structure of dioxygen & superoxide ion: O2 released as dioxygen, not superoxide. Superoxide release: Destructive! Release of highly reactive oxygen species Production of Fe3+ which can NOT bind O2 Dioxygen & Superoxide ion: Leaving as O2 The environment stabilizes oxygen. Ensures O leaves as dioxygen not superoxide ion Distal Histidine: Reduces chance of superoxide release, and acts as a gate keeper for the Fe binding site Makes H bond to O Prevents binding of bulkier like CO- CO binding affinity 230x higher than oxygen for heme group ion with distal histidine....
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This note was uploaded on 10/18/2011 for the course BMB 401 taught by Professor Kaguni during the Fall '08 term at Michigan State University.

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BMB 401 Lecture 10 - BMB 401 Lecture 10 Notes (((Angela-...

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