Chapter 5: Protein Function Flashcards
Myoglobin
Lacks B structure; it is also a classical globular protein; It has a Heme group where oxygen can bind.
Heme
Heme is a type of prosthetic group; an organic compounds that allows protein to carry out some function that the polypeptide can’t do. alone like binding oxygen. The heme is wedged in a hydrophobic area between the helices of E and F of the myoglobin.
O2 Equation
Kd is the binding phenomena in terms of dissociation constants
Fractional Saturation
Proportion of the total myoglobin molecules that have bound O2
Replacing [MbO2] with K equation
pO2; partial pressure of oxygen
760 torr=1atm
Binding O2 to myoglobin shows a hyperbolic curve (p50 is 2.8 torr)
Y is fractional saturation or the proportion of myoglobin molecules that have bound O2
As the O2 conc. increases more O2 molecules bind to the heme groups of myoglobin.
Hemoglobin
A heterotetramer containing two a chains and two B chains. Each subunit is called a globin.
Mb and Hb subunits have similar secondary and tertiary structures.
Mb and Hb subunits are only 18% identical in their 1° structure.
Oxygen binds cooperatively to hemoblogin
Hemoglobins overall oxygen affinity is lower than that of myoglobin: hemoglobin is half-saturated at oxygen 26 torr.
Why is hemoglobin suitable for oxygen transport
The lung pO2 is about 100 torr, hemoglobin is about 95% saturated with O2. The tissues the pO2 is only 20-40 torr, under these conditions O2 released from hemoglobin is taken up by myoglobin in the muscle cells.
Why is hemoglobin suitable for oxygen transport
The lung pO2 is about 100 torr, hemoglobin is about 95% saturated with O2. The tissues the pO2 is only 20-40 torr, under these conditions O2 released from hemoglobin is taken up by myoglobin in the muscle cells.
Effect of O2 binding to the Fe atom of heme group.
When O2 binds to produce oxyhemoglobin the Fe moves into the center of the porphyrin plane. This movement of the Fe ions pulls the His F8 father toward the heem group and this drags the entire F helix so that it moves as much as 1 A. Because of this the hemoglobin now has two quaternary structures that correspond to the deoxy and oxy states.
Hemoglobins two quaternary structures
Hemoglobin is allosteric protein
Allosteric Protein
- multiple subunits/binding sites
- the binding of ligand to one binding site affects the ligand binding affinity of other sites and binding is said to be cooperative
Hemoglobin transports O2 and H+
Distribution in a single cell of cytoskeletal fibers composed of structural proteins
Actin filaments are the most abundant
microfilaments
polymers of the protein actin. Actin polymerization is driven by the hydrolysis of ATP
Actin filament assembly
Collagen structure
Why is glycine so abundant in collagen?
No other amino acid can fit in the center of the strands.
