The Photoactive Excited State of the B12-Based Photoreceptor CarH

• DOI: 10.1021/acs.jpcb.0c09428
• Publication Date: 2020-11-11T16:55:10Z
• Authors: Nicholas A. Miller; April K. Kaneshiro; Arkaprabha Konar; Roberto Alonso-Mori; Alexander Britz; Aniruddha Deb; James M. Glownia; Jake D. Koralek; Leena Mallik; Joseph H. Meadows; Lindsay B. Michocki; Tim B. van Driel; Markos Koutmos; S. Padmanabhan; Montserrat Elías-...; Kevin J. Kubarych; E. Neil G. Marsh; James E. Penner-Hahn; Roseanne J. Sension
• Keywords: Adenosylcobalamin; Homolysis; Quantum yield; Nanosecond

We have used transient absorption spectroscopy in the UV–visible and X-ray regions to characterize excited state of CarH, a protein photoreceptor that uses form B12, adenosylcobalamin (AdoCbl), sense light. With visible excitation, nanosecond-lifetime photoactive is formed with unit quantum yield. The time-resolved near edge structure difference spectrum this demonstrates AdoCbl CarH undergoes only modest structural expansion around central cobalt, behavior similar observed for methylcobalamin rather than free solution. propose new mechanism photoreactivity involving formation triplet state. This allows sensor operate high efficiency without potentially dangerous side products. By stabilizing electronic state, controls reactivity enables slow reactions yield nonreactive products bypass bond homolysis reactive radical species formation.