BCH 380 1st Edition Lecture 11 Outline of Last Lecture I. Protein foldingA. How and WhyII. Forces in Protein folding and stabilityIII. Hydrophobic EffectOutline of Current Lecture IV. MyoglobinB. Structure and locationV. HemoglobinVI. HemeCurrent LectureWhat happens if you heat denature collagen, and then cool?- Staggered, super-helical arrays of tropocollagen triple helices- It becomes a jello-like substanceMyoglobin and Hemoglobin- These are globular proteins that serve as oxygen (O2) storage and carrier proteins, respectively. They bind O2 reversibly, letting go of it when and/or where appropriate. - Myoglobin can be found in whale muscle - It is also found in your heartMyoglobin- Consists of eight alpha helices- The protein contains a heme prosthetic group that binds oxygen.- His-64 forms a hydrogen bond with oxygen, and His-93 is complexes to the iron atom of the hemeHeme- The chemical structure of the Fe(II)-protoporphyrin IX heme group in myoglobin and hemoglobin. The porphyrin ring provides four of the six ligands that surround the iron. The oxygen-binding site in sperm whale myoglobin- Fe(II) lies in the plane of the heme groupRed Blood Cells- Contain hemoglobin Human oxyhemoglobin- Has two alpha and two beta subunits. - The heme groups are shown as stick modelsMyoglobin Vs. Hemoglobin In the Body- Myoglobin has a greater affinity that hemoglobin for oxygen at all oxygen pressures- In the lungs, where the partial pressure of oxygen is high, hemoglobin is nearly saturatedwith oxygen- In tissues, where the partial pressures of oxygen is low, oxygen is released from oxygenated hemoglobin and transferred to myoglobin Oxygen-binding curves of myoglobin and hemoglobin- The oxygen-binding curve of myoglobin is hyperbolic, with half-saturation at an oxygen pressure of 2.8 torr- The oxygen-binding curve of hemoglobin in whole blood is sigmoidal (cooperative), with half-saturation at a pO2 of 26 torro The oxy (R, of high-affinity state) o The deoxy (T, or low-affinity) state of hemoglobin also has a hyperbolic binding curve but a much higher concentration for half-saturationo Solutions of hemoglobin containing both low- and high-affinity forms show sigmoidal binding curves with intermediate oxygen affinities Bohr Effect- Lowering pH decreased the affinity of hemoglobin for