This work was supported by the Institute for Collaborative Biotechnologies through grant W911NF-09-0001 from the U.S. Army Research Office. The content of the information does not necessarily reflect the position or the policy of the Government, and no official endorsement should be inferred. We also acknowledge support by the Packard foundation for Science and Engineering, and the use of NMR facilities funded by the NSF MRSEC grant DMR-1121053. J.M.F. acknowledges support of the Elings Postdoctoral Fellowship, UCSB CNSI. We thank Dr. Alexander Mikhailovsky for the setup and design of time-resolved optical absorption spectroscopy, Devin Edwards and Evan Geller for the setup of the laser-triggered EPR spectroscopy, and Dr. Katherine Stone, Anna Pavlova, Jeda Voska, Christopher Carnabatu, Aye Aye, and Maia Kinnebrew for development of molecular biology and protein purification procedures. The PR gene with the E108Q mutation and His-tag was provided by Dr. Gregg Whited (Genencor). Our work on PR started as a collaboration with Prof. Galen Stucky, Christopher Knoll, Dr. Chi Nguyen, Dr. Hongjun Liang, and Dr. Gregg Whited. We also thank Dr. Brandon Armstrong for apomyoglobin ODNP data given in the Supporting Information.