Abstract

Tetryl, a nitroaromatic compound, was found to interact in two different measurable ways with bacterial reaction centre protein (BRC). The protein amplifies the reaction of tetryl occurring in the presence of detergent, producing a visible product with absorption peaks at 345 nm and 415 nm. BRC provides a location in the micelle with a rate 80-fold faster than in buffer with equal detergent concentration, and a location in the carotenoid binding site when carotenoid is absent with a rate 400-fold faster than in the bulk. The tetryl or its reaction product was also found to bind to the BRC near the bacteriochlorophyll dimer with micromolar level dissociation constant. The binding resulted in slowing down the charge recombination kinetics by modifying the light-induced structural changes. Up to 70% of the protein population can be made to recover with a rate constant of 0.01 s-1, about 100-fold slower than in the dark-adapted conformation.
Both these effects can be combined to design a bimodal biosensor. The change in absorbance at 350 nm can be used to detect tetryl in the ppb (parts-per-billion) concentration range, and photocurrents across a monolayer of BRC on an electrode could be affected by the presence of tetryl. Last, this interaction could be the starting point to the design of bio-hybrid charge-storage devices or completely artificial photosynthetic devices.