Triplet state EPR of reaction centers from the HisL173→LeuL173mutant ofRhodobacter sphaeroideswhich contains a heterodimer primary donor

✍ Scribed by Harry A. Frank; Jennifer Innes; Mila Aldema; Robert Neumann; Craig C. Schenck

• Book ID: 104613827
• Publisher: Springer
• Year: 1993
• Tongue: English
• Weight: 993 KB
• Volume: 38
• Category: Article
• ISSN: 0166-8595
• DOI: 10.1007/bf00015066

✦ Synopsis

Electron paramagnetic resonance (EPR) spectroscopy has been used to examine the triplet states in reaction centers of Rhodobacter sphaeroides which have undergone a genetic modification affecting the primary donor. Reaction centers containing the His L173 ---> Leu L173 substitution in the amino acid sequence have a primary donor which consists of a BChl-BPh heterodimer. The triplets formed in this heterodimer reaction center were compared with those formed in the wild-type reaction center which contains the BChl-BChl homodimer. Both reaction centers transfer triplet energy to the carotenoid under illumination at liquid nitrogen temperatures (~90 K). However, the intensity of the carotenoid triplet signal is significantly decreased in the Leu L173 mutant compared with the wild-type reaction center. At 12 K, in wild-type reaction centers only the primary donor triplet is observed. The Leu L173 mutant exhibits a signal similar to that observed by Bylina et al. (1990) in His M2°° ---> Leu M2°° mutant reaction centers from Rb. capsulatus. The