Fourier transform visible and infrared difference spectroscopy for the study of P700 in photosystem I from Fischerella thermalis PCC 7521 cells grown under white light and far-red light: Evidence that the A–1 cofactor is chlorophyll f

Publication date: Available online 13 April 2019Source: Biochimica et Biophysica Acta (BBA) - BioenergeticsAuthor(s): Gary Hastings, Hiroki Makita, Neva Agarwala, Leyla Rohani, Gaozhong Shen, Donald A. BryantAbstract(P700+ – P700) Fourier transform visible and infrared difference spectra (DS) have been obtained using photosystem I (PSI) complexes isolated from cells of Fischerella thermalis PCC 7521 grown under white light (WL) or far-red light (FRL). PSI from cells grown under FRL (FRL-PSI) contain ~8 chlorophyll f (Chl f) molecules (Shen et al., Photosynth. Res. Jan. 2019). Both the visible and infrared DS indicate that neither the PA or PB pigments of P700 are Chl f molecules, but do support the conclusion that at least one of the A–1 cofactors is a Chl f molecule.The FTIR DS indicate that the hydrogen bond to the 131-keto CO group of the PA pigment of P700 is weakened in FRL-PSI, as might be expected given that the proteins that bind the P700 pigments are substantially different in FRL-PSI (Gan et al., Science 345, 1312–1317, 2014).The FTIR DS obtained using FRL-PSI display a band at 1664 cm−1 that is assigned (based on density functional theory calculations) to the 21-formyl CO group of Chl f, that upshifts 5 cm−1 upon P700+ formation. This is much less than expected for a cation-induced upshift, indicating that the Chl f molecule is not one of the pigments of P700.In WL-PSI the A–1 cofactor is a Chl a molecule with 131-keto and 133-methylester CO mode vi...

Source: Biochimica et Biophysica Acta (BBA) Bioenergetics - April 13, 2019 Category: Biochemistry Source Type: research