Newly identified proteins X, Y, and Z are associated with endoplasmic reticulum (ER) membrane fraction. The above ER membrane fraction is subjected to high salt treatment (buffer pH 7.4, 0.5 M KCl) followed by fractionation by centrifugation into soluble and insoluble pellet components. The following observations were made from the above experiment:
I. The proteins X and Y are fractionated into soluble components.
II. Protein Z is fractionated into insoluble pellet components.

Based on these observations, the following inferences are mode.
A. Proteins X and Y are peripheral membrane proteins
B. Protein Z is an integral membrane protein
C. Protein Z is a peripheral membrane protein
D. Proteins X and Y are integral membrane proteins.

Which one of the following options represents the combination of all correct statements?

Correct option is A

Explanation: The experiment involves fractionating proteins from the endoplasmic reticulum (ER) membrane. Based on the observations:

• Proteins X and Y are fractionated into soluble components. This suggests that X and Y are peripheral membrane proteins. Peripheral proteins are associated with the membrane surface and can be removed by salt treatments or changes in pH.

• Protein Z is fractionated into insoluble pellet components. This suggests that Z is an integral membrane protein. Integral membrane proteins are embedded in the lipid bilayer and cannot be easily removed by salt or pH changes.

Therefore, the correct answer is A and B.

Information Booster:

1. Peripheral membrane proteins are loosely attached to the membrane surface and are often involved in signaling and maintaining the structure of the membrane.

2. Integral membrane proteins are embedded within the lipid bilayer and often play crucial roles in transport, enzymatic activity, or cell signaling.

3. The treatment with high salt helps to differentiate between the two types of proteins by removing peripheral proteins but not integral ones.

4. Peripheral proteins can be dissociated from the membrane by changing the ionic strength or pH, while integral proteins are more tightly bound to the membrane.

5. Peripheral proteins are typically associated with the outer or inner surface of the lipid bilayer.

6. Integral proteins can span the entire membrane and are often involved in transport, cell communication, and energy conversion.

Additional Knowledge:

• Protein Z, being in the insoluble pellet fraction, is most likely an integral membrane protein, firmly embedded in the membrane.

• Proteins X and Y, being in the soluble fraction, are clearly peripheral membrane proteins, which do not span the lipid bilayer but are associated with it.