Membrane proteins synthesized by rabbit reticulocytes.

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Rabbit reticulocyte cells synthesize two major plasma membrane polypeptides.
• Previous studies indicated these proteins originate from membrane-unattached polyribosomes.

Purpose of the Study:

• To determine the location of these synthesized polypeptides within the cell membrane.
• To investigate the synthesis and processing of these membrane proteins.

Main Methods:

• Iodination of whole cells and isolated membranes using lactoperoxidase.
• Enzymatic digestion of whole cells and membranes with chymotrypsin.

Main Results:

• Both predominant polypeptides were found exclusively on the cytoplasmic surface of the cell membrane.
• One polypeptide is synthesized as a precursor, undergoing post-translational cleavage of 20-40 amino acids upon membrane incorporation.

Conclusions:

• The findings indicate that these specific plasma membrane proteins are synthesized on the cytoplasmic side.
• The study provides insights into the synthesis and localization mechanisms of membrane proteins.