One individual, however, expresses only a small number of these molecules—up to six different class I molecules and 12 or more different class II molecules.

TLS Online TPP Program

#Id: 3342

#Unit 6. System Physiology – Plant

Subunit c is a small (Mr 8,000), very hydrophobic polypeptide, consisting almost entirely of two transmembrane helices, with a small loop extending from the matrix side of the membrane

TLS Online TPP Program

#Id: 3343

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 3344

#Unit 6. System Physiology – Plant

Each c subunit has a critical Asp (or Glu) residue about midway across the membrane, which can donate or accept a proton.

TLS Online TPP Program

#Id: 3345

#Unit 6. System Physiology – Plant

The a subunit has a positively charged Arg side chain that forms an electrostatic interaction with the negatively charged carboxylate of Asp on the adjoining c subunit

TLS Online TPP Program

#Id: 3347

#Unit 6. System Physiology – Plant

Arg residue swings aside, forming an interaction with the Asp on the adjacent c subunit in the ring and displacing the proton from that Asp; this adjacent proton exits through the second half- channel to the N side, completing the movement of one proton equivalent from outside to inside the matrix.

TLS Online TPP Program

#Id: 3351

#Unit 6. System Physiology – Plant

The streaming of protons through the F_o pore causes the cylinder of c subunits and the attached ϒ subunit to rotate about the long axis of ϒ, passes through the center of the α₃β₃ spheroid