BIOL 541 1ST Edition Lecture 7 Outline of Last Lecture I. Extract Crystallography Outline of Current Lecture II.Positive Co- operativityIII.Bohr effectIV. Enzymes- KineticsCurrent Lecture Biochemistry Lecture 7- Molecular basis for hemoglobin properties:Positive co-operativity: Oxygen binding on one subunit alters the conformation for other units to accept oxygen readily. This coordinated activity enables bonds to have a low energy state in oxygenated as well as deoxygenated states.1. ASP- Asparatic acid H bond2. GLU- THR H bondOxygen binding: Oxygen displaces HIS and donates 2 unpaired electrons to Fe 4 unpaired electrons. Thus, combine to form 3 pairs of electrons. Low spin state of electrons creates less spin, radius shrinks.Deoxygenated state: Radius large, Fe can not move into the ring.Oxygenated state: Radius small, Fe moves into the ring. Fe is attached to HIS in the helix and pulls HIS. The F helix is pulled to hemoglobin. In turn the bonds stabilizing elbow fulcrum amplifies the tip. 6/10 A HIS moves but the elbow moves a full 1 A. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Loops 90 degrees rotated to the right and make a connection to the sub units in the deoxygenated form.Unstable low state forms, the formation of the bonds drives energy for change in conformation for alpha unit. Exposing Fe to any oxygen and moving F helix not all the way to the center but exposed. Kinetically and mechanically, molecular affinity for oxygen increases as Fe is closer. Oxygen binds to Beta unit and forces alpha unit into the oxygenated conformation. More Fe becomes available and increases alpha unit’s availability for Fe.Bohr Effect- Sensitivity of Hb (hemoglobin) to pH: HIS is a pH sensor. HIS (+) charged when forms an ionic bond when the c=o of the asparatic acid. HIS is not charged in its physiological environment. As asparatic acid increases pka to 3, pH decreases to 7.2 and protonates the imidiazole. The asparatic acid in the F helix moves in to the left. This moves the HIS to the left and Fe moves out of the ring. Therefore, oxygen can not hold on to it as the decrease in pH makes it difficult for oxygen to hold on. 2,3 bisphosphoglycerate (BPG) is (-) charged compound. 2 phosphate groups are attached to COOH ,therefore highly basic site needed for binding. The amino terminus on left binds, HIS 143 to LYS and creates a double dose of basic charge.From the above:- The deoxygenated state of the amino terminus LYS-HIS residue are positioned to bind to BPG. However, BPG occurs only in hypoxia, therefore Hb gives oxygen. NO (nitric oxide) reversible binds to CYS and acts as a vasodilator.In angina patients, nitroglycerate converts to NO and dilates arteries. Richest sources of NO is in the lungs. When Hb reaches the lungs, it picks up NO and binds to CYS. At the edge of the crevice, 2 molecules are exposed inthe oxygenated conformation. CYS reacts with NO and leaves the lungs and circulates throughout the body. Metabolic tissues have lower pH and lower oxygen level causes Hb to shift to deoxygenated state and give off oxygen. As soon as this happens, NO also is given off (reversible reaction). CYS exposed to oxygen causes the conformational change, therefore oxygen is given off by Hb and NO is given off as well. NO dilates the vascular bed of the tissues and increases the blood flow enabling active sites to get more oxygen from the blood flow. Hb is a nano machine which senses the level of oxygen, pH levels, andsenses metabolites and integrates information and delivers oxygen and vasodilates tissue. All this is doneby the 146 amino acids in the Hb molecule.Enzymes:An enzyme is basically an organic catalyst. Catalysts can speed up the rate of reaction without participating in the reaction as well as not changed by the reaction. The term organic refers to its proteinaceous nature. Although a few RNA molecules act enzymatically in splicing off or ligating nucleic acids. DNA acts as a phosphotase and hydrolyses phosphates bond from the amino acids such as TYR, SER, and THR. Life began in RNA and then protein came into being. Today, enzymes are proteases that increase the rate of the reactions that are thermodynamically possible. Thermodynamic refers to down hill reactions but not speed. Example, glucose is enzymatically broken into carbon dioxide and water and is thermodynamically favored. But if sterilized water is used, the reaction is not favorable and is slow. Many enzymes are not permanently changed by the reaction. They may participate briefly but are regenerated at the end.Kinetics: Rate of the reaction depends upon substrate concentration and is ordered based upon the dependent variables. In zero order reactions, the reaction rate is independent of the reactant concentration.First order reactions: Reaction rate is dependent upon single reactant such as substrate converted to product.Second order reactions: Reaction rate is dependent upon 2 substrates converting to product. Large excess of the reactants i.e. 100 x concentration of substrate B than A, then the reaction resembles First order because the level of B is not changing. In other words, pseudo- first order reaction is dependent upon B but B has no effect as it is constant.Michaelis and Menten Model: Enzyme and substrate form intermediate second order reactions as enzyme substrate complex isformed. The enzyme substrate complex has 2 fates: a) dissociate non productive interaction where rate constant=2. b) product formed where rate constant=3. The graph is a hyperbolic curve which approachesthe limit but does not reach it. Therefore, it is difficult to ascertain where velocity is at its