Protein electron transfers at nanomaterial interfaces hold intriguing potential for energy conversion research, and may provide fundamental insight into the link between protein dynamics and reactivity. The ET reactions of cytochrome c with small molecules at the surface of functionalized gold nanoparticles were investigated. Nanoparticle charge and hydrophobicity combined to enhance bimolecular electron transfers. The mechanism appears to involve surface binding of both redox partners, leading to enhanced ET kinetics.