Identification of the vibrational marker of tyrosine cation radical using ultrafast transient infrared spectroscopy of flavoprotein systems

Katalin Pirisi, Lipsa Nag, Zsuzsanna Fekete, James N. Iuliano, Jinnette Tolentino Collado, Ian P. Clark, Ildikó Pécsi, Pierre Sournia, Ursula Liebl, Gregory M. Greetham, Peter J. Tonge, Stephen R. Meech, Marten H. Vos, Andras Lukacs

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Abstract

Tryptophan and tyrosine radical intermediates play crucial roles in many biological charge transfer processes. Particularly in flavoprotein photochemistry, short-lived reaction intermediates can be studied by the complementary techniques of ultrafast visible and infrared spectroscopy. The spectral properties of tryptophan radical are well established, and the formation of neutral tyrosine radicals has been observed in many biological processes. However, only recently, the formation of a cation tyrosine radical was observed by transient visible spectroscopy in a few systems. Here, we assigned the infrared vibrational markers of the cationic and neutral tyrosine radical at 1483 and 1502 cm−1 (in deuterated buffer), respectively, in a variant of the bacterial methyl transferase TrmFO, and in the native glucose oxidase. In addition, we studied a mutant of AppABLUF blue-light sensor domain from Rhodobacter sphaeroides in which only a direct formation of the neutral radical was observed. Our studies highlight the exquisite sensitivity of transient infrared spectroscopy to low concentrations of specific radicals.
Original languageEnglish
Pages (from-to)369–378
Number of pages10
JournalPhotochemical & Photobiological Sciences
Volume20
Issue number3
Early online date22 Feb 2021
DOIs
Publication statusPublished - Mar 2021

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