Chapter 7: Protein Function: Myoglobin and Hemoglobin, Muscle Contraction, and Antibodies

similarities: bind to oxygen molecules by using prosthetic groups called heme groups. differences: myoglobin has a single (monomeric) polypeptide, single heme group, more simple hemoglobin is a tetramer consisting of 4 polypeptides, more complex, contains four heme groups. delivers oxygen to tissues throughout the body

small intracellular protein in vertebrate muscle with 8 helices

Each heme group consists of an organic component called porphyrin and an inorganic component that consists of a single iron atom. The iron atom is located at the center of the organic component and is bound to four different nitrogen atoms

myoglobin and hemoglobin. Both of these proteins have the ability to bind to oxygen molecules by using prosthetic groups called heme groups.

Oxygens diffusion

its major physiological role is to facilitate oxygen diffusion in muscle also oxygen storage protein

the actual binding to the oxygen

hemoglobin cause of 4 subunits need 4 hemes hemes each give one oxygen

hyperbolic due to the high affinity myoglobin with oxygen.

2.8 torr

hemocyanin Hemocyanins, which are exclusively extracellular, in invertebrates, transport O 2 in mollusks and arthropods. e large multimeric proteins that differ in their primary through quaternary structures. However, their oxygen-binding sites are highly similar, consisting of a pair of copper atoms, each liganded by three His residues.

sigmoidal (s) curve because it has a lot smaller binding affinity to oxygen/cooperative interactions

T-state (tense, lacks oxygen) deoxyhemoglobin and the R-state (relaxed, fully oxygenated) oxyhemoglobin

goes from T to R with the addition of oxygen T-state (tense, lacks oxygen) deoxyhemoglobin and the R-state (relaxed, fully oxygenated) oxyhemoglobin

hill equation

26 torr

2β 2tetramer (a dimer of α β protomers) 2 idenical ab dimers

Saturatution-how much of protein is bound to oxygen Partial pressure-concentraion of oxygen

-quicker diffusion The rate at which O 2 can diffuse from the capillaries to the tissues is limited by its low solubility in aqueous solution (∼10 −4 M in blood). Myoglobin increases the effective solubility of O 2 in muscle cells, acting as a kind of molecular bucket brigade to boost the O 2 diffusion rate.

The oxygen-storage function of myoglobin is probably significant only in aquatic mammals such as seals and whales, need it to dive deeper

Hyperbolic

hyperbola

At low pO2, very little O 2 binds to myoglobin (Y O 2 is very small). As the pO 2 increases, more O2 binds to myoglobin. At very high pO2 , virtually all the O2 -binding sites are occupied and myoglobin is said to be saturated with O2.

P50