580.221 BME Molecules and Cells L05 Binding; Hemoglobin p 1Lecture Five – Protein Structure 2 & Binding: Hemoglobin Outline: Structure determines function Coordination; Heme Binding valence Cooperativity; Hill equation I. Review of Fractional OccupancySemipermeable membrane (dialysis) approach: - Receptors on only 1 side, can’t pass membrane - Free ligands equilibrate across membrane - Detect total ligands on each side of membrane ⇒Additional ligands on side with receptors are the bound fraction. Example of this?Red blood cells apply this tactic – by using hemoglobin to bind oxygen, the red blood cells carry many times more oxygen than they could carry simply dissolved in blood. The oxygen diffuses across the cell membrane but the Hb cannot. Derivation of Fractional Occupancy: (R = receptor, L = ligand) for a univalentreceptor-ligand interaction [ ][ ]RLLRKd=so [ ][ ]dKLRRL=[ ]RLRRtotal+=so [ ][ ][ ]dtotalKLRRR+=[ ][ ][ ][ ][ ][ ][ ]LKLKLRRKLRRRLdddtotal+=+==θII. Key VocabularyMyoglobin(Mb)– binds 1 O2, holds oxygen in tissue Hemoglobin(Hb)– binds 4 O2, looks like 4 myoglobins, transports oxygen in red blood cells from lungs to tissues. Heme– prosthetic group for Myoglobin or Hemoglobin that binds O2, consists of porphyrin ring and Fe2+Cooperativity- binding to one site affects binding to other sites on same molecule Hill Coefficient– describes degree of cooperativity Residue/ Side Chain –the moiety on an amino acid that isn’t the backbone of a polypeptide Conformational Change– protein shape change, often induced by binding to another molecule. The conformation of a protein depends on the bond rotations of the polypeptide; and the weak interactions that govern structure.
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