Long-range electron transfer (ET) plays an important role in many bioenergetic processes. Despite the exponential decrease in ET rates with respect to large distances, protein systems efficiently transfer electrons across protein matrices due to oxidized tryptophan and tyrosine hole-hopping intermediates. The redox properties of Trp/Tyr depend on protonation state and thus proton-coupled electron transfer (PCET) plays an essential, but poorly understood, role in these reactions. Conformational states of these redox enzymes also contribute to how ET is facilitated across proteins, as perturbations to enzyme structure can affect donor-acceptor distances and gate ET. The complex between cytochrome c peroxidase (CcP) and cytochrome c (Cc) is a model system for studying inter-protein ET in that it is amenable to both physical and chemical perturbations which can be utilized to probe the underlying ET mechanism. CcP generates a Trp191$^{\bullet+}$ radical to accelerate ET from Cc in the catalytic reduction of H2O2. By substituting Trp191 with Tyr the reaction becomes inactive, but can be partially rescued by introducing a hydrogen bond to Tyr191 from an adjacent general base (Glu/His232). Moreover, by substitution of the CcP heme with a zinc porphyrin (ZnP), the system becomes photoactivatable (ZnCcP). Herein, I investigated how extreme chemical perturbations to the proton environment surrounding Tyr191 in CcP affect ET kinetics. Non-canonical amino acid substitution revealed the necessity of maintaining a nearby proton to Tyr191 for a sufficiently high reduction potential on the tyrosyl radical facilitating ET from Fe(II) Cc. Further, exploring pH and kinetic solvent isotope effects in W191Y:L232E/H ZnCcP:Cc reveal that Tyr191 oxidation becomes rate limiting in the photoexcited system and deprotonation of the general base is necessary for PCET from Tyr191 to ZnP$^{\bullet+}$. Utilizing an irreversible electron quencher, Trp/Tyr191 oxidation was able to be further probed via various EPR spectroscopic techniques providing information on the relative reduction potential of the 191 residue which in the case of Tyr191 is altered by the protonation state of the nearby base. These studies define the protic conditions in which ET can be effectively turned on and off in engineered ET systems. To further perturb the stability of CcP:Cc, I utilized sortase-mediated ligation to covalently fuse the complex into a multidomain single molecule. In the fusion proteins, the molecular conformation and the sampling of productive interfaces depended substantially on linker length. Moreover, the structural variability between the unimolecular proteins gated ET and significantly affected reactivity. These findings underscore that specific interaction modes between redox partners influence electronic communication and reveal that interdomain linkers can influence the sampling of productive conformations. Finally, by applying extreme physical perturbations through high-temperature and pressure x-ray crystallography, I found that CcP responded mostly to high-pressure with volume declines at the periphery of the protein but maintains nearly intransient core structure, hydrogen bonding interactions and active site channels. This work demonstrated that encapsulation of the active-site heme by the protein peptide can provide a precisely structured environment resistant to change across a wide range of physical conditions.