An arginine residue (Arg 210) in the matrix-side proton channel of the a subunit of ATP synthase is near the aspartate residue (Asp 61) in the c ring subunit. How might Arg 210 assist proton flow?

a) Arg 210 and Asp 61 will interact by charge repulsion to facilitate proton binding.
b) Arg 210, with its positive charge, will facilitate the release of a proton from Asp 61 by stabilizing the negative charge of its acidic side chain.
c) Both Arg 210 and Asp 61 allow for proton flow due to hydrophobic forces.
d) both a and c are correct.
e) both b and c are correct.