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

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.

2-Alkylsulphanyl-4-pyridinecarbothioamides — inhibitors of oxygen evolution in freshwater alga Chlorella vulgaris

The inhibition of the oxygen evolution rate (OER) in Chlorella vulgaris by 2-alkylsulphanyl-4-pyridinecarbothioamides (APCTs; alkyl = methyl up to hexadecyl) was studied. APCTs were found to inhibit photosynthetic electron transport (PET) which resulted in the inhibition of OER in algae. The inhibitory activity of APCTs was highly dependent on the alkyl chain length of the 2-alkylsulphanyl substituent and the corresponding dependence showed a bilinear course with the decyl derivative as being the most active inhibitor. Using EPR spectroscopy, the site of APCT action in the algal photosynthetic apparatus was determined. It was confirmed that APCT interacted mainly with the D. intermediate, i.e. with tyrosine radical (TyrD) occurring at the 161st position in D2 protein which is situated on the donor side of photosystem 2.