Hemoglobin & Myoglobin & Collagen

Heme proteins Supply of oxygen Myoglobin Oxidative metabolism Monomeric protein of red muscle Stores oxygen

Hemoglobin O2 transport Tetrameric Cooperative interactions

Normal Hemoglobins Hb A (α2β2) Hb F (α2γ2) Major normal adult hemoglobin Comprising about 97% of the total Hb F (α2γ2) Major hemoglobin of the fetus Increased oxygen affinity Lower affinity for 2,3-diphosphoglycerate (DPG)

Embryonic Hemoglobins Hb A2 (α2δ2) 1.5-3.5% of normal adult Increased Hb A2 β-thalassemias Embryonic Hemoglobins Hb Gower-1 (ζ2ε2) HbPortland (ζ2γ2) Hb Gower-2 (α2ε2)

Developmental pattern of the quaternary structure of fetal and newborn hemoglobins

Heme & ferrous iron Fe2+ linked to all four nitrogen atoms of the heme, to histidine F8, and, in oxyMb & oxyHb, also to O2

Heme

Myoglobin O2 storage Rich in α Helix 153-aminoacyl residue MW 17,000 75% in eight right-handed Helices A–H Surface of myoglobin is polar Interior contains only nonpolar Leu, Val, Phe,

A model of myoglobin

Myoglobin Histidines F8 & E7 Roles in Oxygen binding Proximal histidine, His F8 The fifth coordination position of the iron O2 occupies the sixth coordination position

Hemoglobin Tetrameric the α polypeptide α2β2 (HbA) α2γ2 (HbF) α2S2 (HbS) α2δ2 (HbA2) the α polypeptide Seven helical regions bind four molecules of O2 per tetramer

Cooperative binding A molecule of O2 binds to a hemoglobin tetramer more readily if other O2 molecules are already bound

P50 expresses the relative affinities of different hemoglobins for oxygen The partial pressure of O2 that half-saturates Hb P50 for HbA and fetal HbF 26 and 20 mm Hg HbF,High affinity for O2

On oxygenation of hemoglobin, the iron, histidine F8, and linked residues move toward the heme ring.

The iron atom moves into the plane of the heme on oxygenation. Histidine F8 and its associated residues are pulled along with the iron atom.

rupture of salt bridges T (taut) state to the R (relaxed) state Oxygenation of hemoglobin is accompanied by large conformational changes binding of the first O2 Iron motion rupture of salt bridges T (taut) state to the R (relaxed) state Low affinity and high-affinity conformations

The transition between the two structures is influenced by protons, carbon dioxide, chloride, and BPG; the higher their concentration, the more oxygen must be bound to trigger the transition.

After releasing O2 at the tissues, hemoglobin transports CO2 & protons to the lungs CO2 as carbamates 15% of the CO2 in venous blood Remaining

One proton for every two O2 molecules released In the lungs, as O2 binds to deoxyhemoglobin, protons are released and combine with bicarbonate to form carbonic acid.

Bohr effect O2 Binds Reciprocal coupling of proton and O2 binding Rupture of Salt Bonds Proton release

The Bohr effect

Increase in proton concentration Increase in PO2 R state Oxygenated breaks salt bridges Release of O2 the T structure Salt bridges re-form Increase in proton concentration Enhances the release of O2 Increase in PO2 Promotes proton release

2,3-Bisphosphoglycerate (BPG) Stabilizes the T Structure of Hemoglobin deoxyhemoglobin Low PO2 Promotes the synthesis Forming additional salt bridge

Mode of binding of 2,3-bisphosphoglycerate to human deoxyhemoglobin Mode of binding of 2,3-bisphosphoglycerate to human deoxyhemoglobin. BPG interacts with three positively charged groups on each β chain.

Adaptation to High Altitude Increase in Number of erythrocytes Concentrations of hemoglobin BPG

Myoglobinuria Massive crush injury Myocardial infarction Urine dark red Myocardial infarction

Anemias Reductions in Number of red blood cells Hemoglobin Folic acid or vitamin B12 deficiency Hemoglobin Iron deficiency

Glycosylated Hemoglobin (HbA1c) ε-amino group of lysine residues Amino terminals Normal,about 5% Proportionate to blood glucose concentration Reflects the mean blood glucose concentration over the preceding 6–8 weeks For management of diabetes mellitus

Numerous mutant human hemoglobins have been identified Hemoglobinopathies & Thalassemias

Collagen a Fibrous Protein the most abundant of the fibrous proteins 25% of the protein mass in body Strength & flexibility of skin Collagen & keratin fibers Bones & teeth elongated proteins repetitive amino acid sequences regular secondary structure

Collagen Primary, secondary, and tertiary structures of collagen

Collagen Rich in proline & hydroxyproline repetitive Gly-X-Y pattern Y generally is proline or hydroxyproline

Collagen maturation Collagen Is Synthesized as a Larger Precursor Procollagen Prolyl hydroxylase Lysyl hydroxylase

Collagen Collagen triple helices are stabilized by Hydrogen bonds Residues in different polypeptide chains. Hydroxyprolyl & hydroxylysyl Covalent cross-links between Modified lysyl residues both within and between polypeptide chains.

Hydroxylysyl residues Glucosyl or galactosyl residues Removal of the globular amino terminal & carboxyl terminal Cross-link Certain lysyl residues are modified Lysyl oxidase Copper-containing ε-amino groups to aldehydes aldol condensation C=C double bond C-N bond Strength & rigidity

Order and location of processing of the fibrillar collagen precursor

Disorders of collagen maturation Nutritional Scurvy Deficiency of vitamin C Prolyl & lysyl hydroxylases Bleeding gums, swelling joints, poor wound healing Copper Deficiency Lysyl oxidase

Disorders of collagen maturation Genetic Osteogenesis imperfecta Fragile bones Ehlers-Dahlos syndrome Connective tissue disorders Defects in the genes α collagen-1 Procollagen N-peptidase Lysyl hydroxylase Mobile joints & skin abnormalities