MCB 450 1st Edition Lecture 13Outline of Last Lecture I. Catalytic strategies used by enzymesII. Inhibition of enzyme activityIII. Example of an enzyme mechanism:a. peptide hydrolysis by chymotrypsinOutline of Current Lecture I. Enzyme Regulation: AllosteryII. Conformational Changes in Hemoglobin upon O2-bindingIII. Other Ways to Regulate EnzymesCurrent LectureRegulation of enzyme activity-Allosteric enzymes always catalyze the committed step of metabolic pathwaysRegulatory step in many biosynthetic pathways is catalyzed by an allosteric enzyme-Feedback inhibition is a common means of biochemical regulationAllosteric interactions: the "concerted" model-Allosteric constant - (L0) T/R ratio-Symmetry rule - all must be in the T form or all must be in the R form Heterotropic versus homotropic-Heteroptropic = regulators-Homotropic = substratesAllosteric interactions: "sequential" model -Enzymes are studied one at a time to gain more information about themMyoglobin vs hemoglobin-Hemoglobin - carries oxygen from the lungs to the tissues and contributes to the transport of carbon dioxide and hydrogen ions back to the lungs-Myoglobin - located in muscle and may facilitate the diffusion of oxygen to cellular sites that require oxygen and provide a reserve supply of oxygen in times of needO2-binding by hemoglobin and myoglobin-pO2 = partial pressureO2-binding by hemoglobin-Protoporphyrin - organic component in heme, made up of four pyrrole rings linked by methine bridges to form a tetrapyrrole ring, four methyl groups, two vinyl groups, and twopropionate side chains are attachedThese 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.-Proximal histidine - occupies 5th coordination site on hemeQuaternary structure of hemoglobin-Globin fold - alpha-helices that are linked to one another by turns to form a globular structureConformational changes in hemoglobin-3-D structure of hemoglobin is described as a pair of identical alpha-beta dimers that associate to form the hemoglobin tetramerAllosteric Hb is not only regulated by substrate (O2)-binding, but also by allosteric effector molecules that bind Hb-2,3-bisphosphoglycerate (BPG) -- allosteric regulator molecule present in red blood cellsFetal Hb binds 2,3-BPG with lower affinity-Fetal hemoglobin - must bind oxygen when the mother's hemoglobin is releasing oxygen-Sickle-cell anemia ogenetic, must be homozygous for geneo heterozygous --not usually symptomatic, normally just a carrier, and is resistant to malaria which is why it is prevalent in
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