State of Association of Membrane Proteins
The native environment of a membrane protein can be closely simulated by the small micelles formed by appropriate detergents. This permits solubilization of membrane proteins with retention of their native structure and biological activity. Molecular weights and polypeptide chain compositions can then be determined by well-established methods of solution physical chemistry. We have found that some membrane proteins (e.g., cytihrome b5) are monomeric, whereas others are oligomeric. The Ca++-stimulated ATPase from sarcoplasmic reticulum appears to be a trimer (possibly tetramer) of identical polypeptide chains. Each chain has two very similar halves, which suggests that the trans-membrane portion of this protein consists of six (possibly eight) symmetrically arranged elemetIT, which perhaps create an aqueous channel for the passage of Ca++ ions through the membrane.
KeywordsSodium Dodecyl Sulfate Sarcoplasmic Reticulum Polypeptide Chain Phospholipid Bilayer Phospholipid Vesicle
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