Primary photochemistry of the dark- and light-adapted states of the YtvA protein from Bacillus subtilis.

The primary (100 fs to 10 ns) and secondary (10 ns to 100 μs) photodynamics in the type II light-oxygen-voltage (LOV) domain from the blue light YtvA photoreceptor extracted from Bacillus subtilis were explored with transient absorption spectroscopy. The photodynamics of full-length YtvA were characterized after femtosecond 400 nm excitation of both the dark-adapted D447 state and the light-adapted S390 state. The S390 state relaxes on a 43 min time scale at room temperature back into D447, which is weakly accelerated by the introduction of imidazole.

Unraveling the Primary Isomerization Dynamics in Cyanobacterial Phytochrome Cph1 with Multi-pulse Manipulations.

The ultrafast mechanisms underlying the initial photoisomerization (P → Lumi-R) in the forward reaction of the cyanobacterial photoreceptor Cph1 were explored with multipulse pump-dump-probe transient spectroscopy. A recently postulated multi-population model was used to fit the transient pump-dump-probe and dump-induced depletion signals. We observed dump-induced depletion of the Lumi-R photoproduct, demonstrating that photoisomerization occurs via evolution on both the excited- and ground-state electronic surfaces.

Chemical inhomogeneity in the ultrafast dynamics of the DXCF cyanobacteriochrome Tlr0924.

Cyanobacteriochromes (CBCRs) are diverse biliprotein photosensors distantly related to the red/far-red photoreceptors of the phytochrome family. There are several subfamilies of CBCRs, displaying varied spectral responses spanning the entire visible region. Tlr0924 belongs to the DXCF subfamily that utilizes the Cys residue in a conserved Asp-Xaa-Cys-Phe (DXCF) motif to form a second covalent linkage to the chromophore, resulting in a blue-absorbing dark state.

Femtosecond photodynamics of the red/green cyanobacteriochrome NpR6012g4 from Nostoc punctiforme. 2. reverse dynamics.

Phytochromes are red/far-red photosensory proteins that utilize photoisomerization of a linear tetrapyrrole (bilin) chromophore to photoconvert reversibly between red- and far-red-absorbing forms (P(r) and P(fr), respectively). Cyanobacteriochromes (CBCRs) are related photosensory proteins with more diverse spectral sensitivity. The mechanisms that underlie this spectral diversity have not yet been fully elucidated.

Femtosecond photodynamics of the red/green cyanobacteriochrome NpR6012g4 from Nostoc punctiforme. 1. Forward dynamics.

Phytochromes are well-known red/far-red photosensory proteins that utilize the photoisomerization of a linear tetrapyrrole (bilin) chromophore to detect the ratio of red to far-red light. Cyanobacteriochromes (CBCRs) are related photosensory proteins with a bilin-binding GAF domain, but much more diverse spectral sensitivity, with five recognized subfamilies of CBCRs described to date. The mechanisms that underlie this spectral diversity have not yet been fully elucidated.

Second-chance forward isomerization dynamics of the red/green cyanobacteriochrome NpR6012g4 from Nostoc punctiforme.

The primary ultrafast Z-to-E isomerization photodynamics of the phytochrome-related cyanobacteriochrome NpR6012g4 from Nostoc punctiforme was studied by transient absorption pump-dump-probe spectroscopy. A 2 ps dump pulse resonant with the stimulated emission band depleted 21% of the excited-state population, while the initial photoproduct Lumi-R was depleted by only 11%. We observed a red-shifted ground-state intermediate (GSI) that we assign to a metastable state that failed to isomerize fully.

Multiphoton manipulations of enzymatic photoactivity in aspartate aminotransferase.

The aspartate aminotransferase (AAT) enzyme utilizes the chromophoric pyridoxal 5'-phosphate (PLP) cofactor to facilitate the transamination of amino acids. Recently, we demonstrated that, upon exposure to blue light, PLP forms a reactive triplet state that rapidly (in microseconds) generates the high-energy quinonoid intermediate when bound to PLP-dependent enzymes [J. Am.