Efficient conditions for the photoaccumulation of H A− in the photosynthetic reaction centre of Rhodobacter sphaeroides R26 with uniformly labelled bacteriopheophytin monitored by Fourier transform infrared difference spectroscopy

Abstract

The native bacteriopheophytins (BPheo) a at sites H A and H B in the reaction centre (RC) of Rhodobacter sphaeroides R26 have been exchanged with uniformly 13 C , 15 N labelled BPheo a. Exchange at the H A site was >50% as monitored with light-induced FTIR-difference spectroscopy indicated by the shift of the band at 1590 cm −1. The photoreduction of H A has been monitored by light-induced FTIR-difference spectroscopy at 22°C in the presence of reductant and mediator: either sodium dithionite and cytochrome c, or sodium dithionite and dyes (potassium indigotetrasulfonate, neutral red). New experimental conditions are described for H A − photoaccumulation, and light-induced FTIR-difference spectra characteristic of H A − are reported. The H A −/H A FTIR-difference spectra of Rb. sphaeroides R26 RCs in which uniformly 13 C , 15 N labelled BPheo a replaces the photoactive BPheo will allow the BPheo modes to be assigned and to be discriminated from those of the RC protein.