The muscarine-sensitive type of acetylcholine

The muscarine-sensitive type of acetylcholine
receptor is a protein that contians seven transmembrane
subunits (4). Since each exists in the
form of an ! helix, it is referred to as a sevenhelix
transmembrane protein (p. 270). The
amino end (NH2) lies extracellularly; the carboxy
end (COOH), intracellularly. The transmembrane
domains are connected by intracellular
and extracellular polypeptide loops (4).
Different domains of the whole protein are distinguished
(5) according to location and the
relative proportion of hydrophilic and hydrophobic
amino acids. The amino end and the carboxy
end each form a domain just like the intracellular
(a–c), and extracellular portions (d–f).