BMB 401 Lecture 4: Exercise 2.4a

• School: University of Miami
• Department: Biochemistry and Molecular Biology
• Course: BMB 401
• Professor: Farooq

Document Summary

Mb stores oxygen and is mostly in muscle tissues. It has a hyperbolic oxygen-binding curve (non- cooperative response). Hb carries oxygen in bloodstream from lungs to tissues. It has a sigmoidal oxygen-binding curve (cooperative response). Both have the prosthetic group (type of cofactor) heme. Only 28/150 residues are the same between hb and mb (18% similarity). All 3 polypeptide chains share remarkably similar 3d structure (convergent evolution = same structure and function but different evolution). This said the a and b chain of hb are evolutionarily related to each other and to the mb polypeptide chain so it cannot be convergent surprisingly. Heme is composed of 4 pyrrole rings linked via methine bridges. In the middle is the iron mtal ion fe2+ (fe(ii)). Fe(ii) is stabilized via 5 ligands: one n from each of 4 pyrrole groups and an extra n from a histidine (phi8 histidine) on proximal face of heme.