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Reaction centers of the thermophilic microaerophile, Chloracidobacterium thermophilum (Acidobacteria) I: biochemical and biophysical characterization

Journal Article · · Photosynthesis Research
 [1];  [2];  [2];  [2];  [2];  [3]
  1. Pennsylvania State Univ., University Park, PA (United States); OSTI
  2. Pennsylvania State Univ., University Park, PA (United States)
  3. Pennsylvania State Univ., University Park, PA (United States); Montana State Univ., Bozeman, MT (United States)

Chloracidobacterium thermophilum is a microaerophilic, anoxygenic member of the green chlorophototrophic bacteria. This bacterium is the first characterized oxygen-requiring chlorophototroph with chlorosomes, the FMO protein, and homodimeric type-1 reaction centers (RCs). The RCs of C. thermophilum are also unique because they contain three types of chlorophylls, bacteriochlorophyll aP esterified with phytol, Chl aPD esterified with Δ2,6-phytadienol, and Zn-BChl aP' esterified with phytol, in the approximate molar ratio 32:24:4. The light-induced difference spectrum of these RCs had a bleaching maximum at 839 nm and also revealed an electrochromic bandshift that is probably derived from a BChl a molecule near P840+. The FX [4Fe–4S] cluster had a midpoint potential of ca. - 581 mV, and the spectroscopic properties of the P+ F$$^-_X$$ spin-polarized radical pair were very similar to those of reaction centers of heliobacteria and green sulfur bacteria. The data further indicate that electron transfer occurs directly from A0- to FX, as occurs in other homodimeric type-1 RCs. Washing experiments with isolated membranes suggested that the PscB subunit of these reaction centers is more tightly bound than PshB in heliobacteria. Thus, the reaction centers of C. thermophilum have some properties that resemble other homodimeric reaction centers but also have specific properties that are more similar to those of Photosystem I. These differences likely contribute to protection of the electron transfer chain from oxygen, contributing to the oxygen tolerance of this microaerophile.

Research Organization:
Pennsylvania State University, University Park, PA (United States); Arizona State University, Tempe, AZ (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
FG02-94ER20137; SC0010575
OSTI ID:
1800808
Journal Information:
Photosynthesis Research, Journal Name: Photosynthesis Research Journal Issue: 1 Vol. 142; ISSN 0166-8595
Publisher:
SpringerCopyright Statement
Country of Publication:
United States
Language:
English

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