Answer to Question #30877 in Organic Chemistry for jeanette

Question

Apart from differences in amino acid ligands what is the fundamental difference between the way in which the cytochrome cofactor is bound to cytochromes such as myoglobin and respiratory cytochromes like cytochrome c?

Answer 1

Hemoglobin and Myoglobin are examples of hemeprotein that are essential in the storing and transports of oxygen in mammals. Hemoglobin is a quaternary protein that occurs in the red blood cell, whereas, myoglobin is a tertiary protein found the muscle cells of mammals. Although they might differ in location and size, their function are similar. Being hemeproteins, they both contain a prosthetic group. His-F8 of the myoglobin, also known as the proximal histidine is covalently bonded to the 5th coordination position of the iron. And as an Oxygen binds to the 6th coordination position of the iron, a distal histidine (a histidine that doesn't bond directly with the Iron), His-E7 of the myoglobin binds to the Oxygen that is now covalently bonded to the iron. The same occurs for the hemoglobin, however, being a protein with 4 subunits, the hemoglobin contains 4 heme, therefore, allowing 4 Oxygen atoms to bind to the heme. Myoglobin and hemoglobin are globular proteins that serve to bind and deliver oxygen. These globins dramatically improve the concentration of molecular oxygen that can be dissolved in the biological fluids of vertebrates and some invertebrates. Both of these globins contain an organic prosthetic group for binding oxygen and they contain many similar structural characteristics. Yet the differences in function between these two proteins can be explored from a structural perspective, leading to a discourse on ligand binding and allosteric regulation.