Question

7. Describe the effect of each of the treatments below on the various types of membrane proteins. Would the treatment release a peripheral protein from the membrane? An integral protein? A peripheral protein covalently attached to a lipid anchor? a) Changes in pH b) Changes in ionic strength c) Detergent d) Urea e) Phospholipase C

Answer 1

There are mainly five membrane proteins. they are

1. Transport proteins: These transmembrane proteins can form a pore or channel in the membrane that is selective for certain molecules.

2. Enzymes: these proteins have enzymatic activity.

3. signal transduction proteins.

4. Recognition proteins.

5. Joining proteins.

Integral membrane proteins have some of their mass in the lipid bilayer. Usually these binding sites are on integral membrane proteins, although non specific binding of lipid bilayer is also possible. Peripheral membrane proteins can be removed from the membrane with mild treatments. Lipid- anchored proteins insert and assume a place in the bilayer structure of the membrane alongside the similar fatty acid tails.

a. Changes in pH: Decreasing the pH by adding an acid coverts -COO- ion to a neutral -COOH group. In each case the ionic attraction disappears, and protein shape unfolds. Various amino acid chain can hydrogen bond to each other. Changing the pH disrupts the hydrogen bonds, and this changes the shape of protein.

b. Changes in ionic strength : With increasing ionic strength of the solution, an increase of the protein concentration reduces the attractive intractive parameter that leads to an increase of repulsive interaction.

c. Detergent: Both proteins and detergent have hydrophobic and hydrophylic sides, the detergent is attracted to these forcesand proteins apart.

d. Urea: Proteins can be denatured by urea through several processes. One method involves direct interaction whereby urea hydrogen bonds to polarized areas of charge, such as peptide groups. urea can denature proteins indirectly, through affecting the attributes of the solvent in which the proteins are immersed.

e. Phospholipase C: It reacts with protein and stimulates of G- protein- coupled receptors causes hydrolis of substrates resulting in the formation of two second messengers.