1. Hemoglobin and the Movement of Oxygen M 221 Medical Biochemistry Fall 2017 Dr. Nabil Bashir

Hemoglobin and the Movement of Oxygen Specific objectives The student must understand the process of oxygen binding, specifically; Oxygen binding and iron movement - deoxy versus oxygenated state  Iron-oxygen binding  Quaternary structure of deoxyhemoglobin  Oxygen binding of myoglobin  Oxygen binding of hemoglobin 

Hemoglobin and the Movement of Oxygen Specific objectives 2. The student must understand the concept of cooperativity, specifically; Cooperativity in hemoglobin's oxygen binding  Quaternary changes on oxygen binding by hemoglobin  T to R transition  Sequential model of binding  The effect of 2,3 BPG  Binding of 2,3BPG to hemoglobin  Oxygen binding and fetal hemoglobin 

Hemoglobin and the Movement of Oxygen Specific objectives 3. The student must understand molecular aspects of Bohr Effect, specifically; Effect of pH on oxygen affinity of hemoglobin  Carbon dioxide and pH  Carbon dioxide effects  Carbamate formation  Transport of CO2 to lungs 

Hemoglobin and the Movement of Oxygen Specific objectives 4. The student must know some Hemoblobin Genetic Considerations; Sickled blood cells  and hemoglobin fibers  Sickle cell traits and malaria 

Hemoglobin and the Movement of Oxygen Introduction Animals Have Widely Varying Needs for Oxygen Demand for Oxygen Can Change in Seconds Basal Needs are Significant - Diffusion not Enough Exercise, Fight/Flight Add to the Need ATP Energy Produced Aerobically 15 Times More Efficiently Than Anaerobically Respiration versus Fermentation Efficient, Adaptable Oxygen Delivery is Necessary

Quaternary Structure Interaction of multiple protein subunits Hemoglobin - 4 Subunits (α2β2), 1 Heme Each, 1 O2 Each, 1 “Donut Hole” Myoglobin - 1 Subunit, 1 Heme, 1 O2 Each

Hemoglobin and the Movement of Oxygen Structure and Function Heme Prosthetic Group Ferrous Iron - Methemoglobin Won’t Work Only Fe++ Binds Oxygen

Hemoglobin and the Movement of Oxygen Structure and Function Edge-on View Attached to Remainder of Global Subunit Histidine’s Movement Changes Global Unit’s Shape

Hemoglobin and the Movement of Oxygen Cooperativity Affected by O2 Binding )R-State)0 Fully Oxygenated (R-State( No Oxygen )T-State( Exiting Lungs Entering Lungs Oxygen Bound Affected by O2 Binding R-State Binding of the first O2 favors binding of second, etc. - Cooperatively Cooperatively Important as Hemoglobin Rapidly Passes Through Lungs

Hemoglobin and the Movement of Oxygen At High O2, Both Hold 100% Hemoglobin and the Movement of Oxygen Cooperativity At Low O2, Myoglobin Holds More than Hemoglobin Hyperbolic Binding Curve Sigmoidal Binding Curve As Curves Move to Right Less Affinity for Oxygen Myoglobin Better for Storing Oxygen Hemoglobin Better at Delivering Oxygen

Hemoglobin and the Movement of Oxygen Bohr Effect Less Oxygen Bound at Same Pressure Less Affinity More Affinity Protons Can Bind to Hemoglobin Protons Change Hemoglobin’s Shape Reshaped Hemoglobin Loses Oxygen Rapidly Metabolizing Tissues Release Protons Rapidly Metabolizing Tissues Get More Oxygen From Hemoglobin More O2 Required To Have Same Fraction Bound

Hemoglobin and the Movement of Oxygen Bohr Effect & CO2 Acid Favors Release of O2 From Hemoglobin CO2 Favors Release of O2 From Hemoglobin Acid and CO2 are Released by Rapidly Metabolizing Tissues

Hemoglobin and the Movement of Oxygen 2,3 BPG Byproduct of Glycolysis Exercising Muscle Cells Rapid Use Glycolysis Exercising Muscle Cells Produce Acid, CO2, and 2,3 BPG Binds in Hole of Donut Locks Hemoglobin in T-State 2,3 Bisphosphoglycerate

Hemoglobin and the Movement of Oxygen 2,3 BPG and Oxygen Binding Slow Metabolic Rate Rapidly Metabolizing Cells Produce Acid Rapidly Metabolizing Cells Release CO2 Rapidly Metabolizing Cells Release 2,3 BPG All Favor O2 Release from Hemoglobin So Rapidly Metabolizing Cells Get More O2 Fast Metabolic Rate

Hemoglobin and the Movement of Oxygen 2,3 BPG and Smoking 2,3 BPG Big Concern for Smokers Blood of Smokers has High Levels of 2,3 BPG Hemoglobin Gets Locked in T-state in Passage Through Lungs Oxygen Carrying Capacity of Blood Reduced Carbon Monoxide Levels Also Higher in Smokers 2,3 Bisphosphoglycerate

Hemoglobin and the Movement of Oxygen Movement of CO2 HbO + H+ O2 Blood Rapidly Metabolizing Tissue H+:Hb-CO2 Some Remainder H2O Blood H+:Hb-CO2 HbO Exhaled HbO H2O + CO2 Lungs O2 + H+:Hb-CO2

Hemoglobin and the Movement of Oxygen Carbon Monoxide and Heme An Additional Histidine is Present at the Heme Iron Site Reduces Affinity to CO, but Does Not Eliminate it Carbon Monoxide in Cigarette Smoke Note That CO2 Does Not Bind to Heme, nor do Protons

Hemoglobin and the Movement of Oxygen Fetal Hemoglobin The Body Makes Different Globins Over Time Most Variations Centered on Birth Fetal Hemoglobin Mostly α2γ2 High Most of Life At Adult Levels by 24 Weeks Highest in Fetus

Hemoglobin and the Movement of Oxygen Fetal Hemoglobin Fetal Hemoglobin Can’t Bind to 2,3 BPG Mostly Remains in R-state Increasing Affinity

Hemoglobin and the Movement of Oxygen Sickle Cell Anemia Sickle Cell Anemia is a Genetic Disease Affecting Hemoglobin Multiple Forms - Mutation of Glu to Val at Position #6 Most Common Red Blood Cells Lose Rounded Shape and Form Sickles Shape Change Happens in Low O2 Conditions - Exercise Change Caused by Polymerization of Hemoglobin Sickled Cells

Hemoglobin and the Movement of Oxygen Sickle Cell Anemia Rounded Cells Move Easily Through Capillaries Sickled Cells Get Stuck Sickled Cells Removed by Spleen

Hemoglobin and the Movement of Oxygen Sickle Cell Anemia Why is Sickle Cell Anemia so Widespread? Why Has it Not Been Selected Against? Greatest Incidence of Sickle Cell Anemia Greatest Incidence of Malaria

Hemoglobin and the Movement of Oxygen Sickle Cell Anemia Benefit of Sickle Cell Mutation for Heterozygotes No Benefit to Homozygous Recessive or Dominant

Hemoglobin and the Movement of Oxygen Summary Animals Have Widely Varying O2 Needs ATP Generated Much More Efficiently in Presence of O2 Hemoglobin and Myoglobin are Related, but Have Different Functions Hemoglobin has Four Subunits and Hemes. Myoglobin has One of Each Bind of O2 by Heme’s Iron Pulls up on a Histidine and Change’s Hemoglobin’s Shape Changing Hemoglobin’s Shape Converts Hemoglobin from T-state to R-state R-state Binds Oxygen Better. T-state Releases O2 Better In the Bohr Effect, Binding of CO2 and H+ Favors O2 Release The Bohr Effect Explains How Oxygen and CO2 Exchanged in Lungs 2,3 BPG is Produced by Rapidly Metabolizing Cells. It too Favors O2 Release Fetal Hemoglobin Can’t Bind 2,3 BPG and has Greater O2 Affinity Than Adult Hemoglobin Sickle Cell Anemia (SCA) is a Genetic Disease of Hemoglobin In Low O2 Concentration, Red Blood Cells of SCA Sufferers Form Sickle Shapes Sickled Cells Stick in Capillaries and Can be Fatal People Heterozygous for the Mutated Gene Survive Malaria Better Than Others