Abstract
Spectrally pure reaction center preparations from Chloroflexus aurantiacus have been obtained in a stable form; however, the product contained several contaminating polypeptides. The reaction center pigment molecules (probably three bacteriochlorophyll a and three bacteriopheophytin a molecules) are associated with two polypeptides (Mr = 30000 and 28000) in a reaction center complex of Mr = 52000. No carotenoid is present in the complex. These data together with previous spectral data suggest that the Chloroflexus reaction center represents a more primitive evolutionary form of the purple bacterial reaction center, and that it has little if any relationship to the green bacterial component. A reaction center preparation from Rhodopseudomonas sphaeroides R26 was fully denatured at 50°C while the Chloroflexus reaction center required higher temperatures (70-75°C) for complete denaturation. Thus, an intrinsic membrane protein of a photosynthetic thermophile has been demonstrated to have greater thermal stability than the equivalent component of a mesophile.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 322-326 |
| Number of pages | 5 |
| Journal | BBA - Bioenergetics |
| Volume | 723 |
| Issue number | 2 |
| DOIs | |
| State | Published - May 27 1983 |
| Externally published | Yes |
Funding
From the data available here and in Ref. 8 we conclude that the Chloroflexus reaction center may be an earlier version of the purple bacterial reac- tion center. The significance of one BChl a molecule apparently s,bstituting for a BPh molecule and the addition of a third polypeptide to the reaction center complex during the evolution of purple bacterial reaction centers is unknown. It is tempting to equate the 30 and 28 kDa polypeptides of the Chloroflexus reaction center with the M and L subunits \[13\]o f the purple bacterial component, since all the chromophore molecules in the latter have been shown to be associated only with two (M and L) polypeptides \[1 2,13\]. Immunochemical and/or sequence studies will reveal their correct phylogenetic relationship. The difference in thermal stability between the two reaction center preparations (Figs. 2 and 3) confirms expectations that hydrophobic intrinsic membrane proteins, as well as soluble proteins, have increased thermal stability in thermophilic organisms \[9\]. Recent studies on some of the photochemical reactions in membranes of C aurantiacus \[14\] are also consistent with the notion that this reaction center has several features in common with those of the purple bacteria. The stability of the reaction center complex during electrophoresis proved fortunate. It revealed that all the spectral characteristics previously described for the Chloroflexus reaction center \[8\] are associated with a single complex with an apparent size of 52 kDa and having two apoproteins of 30 and 28 kDa probably present in a 1 : 1 ratio, and furthermore that the Chloroflexus reaction center was stable when its protein was represented by only two polypeptides (cf. LM stability in Rps. sphaeroides reaction centers). Electrophoresis also showed that the purification procedure used does not yield pure reaction centers, since at least nine contaminating polypeptides are present (Fig. 1). Ammonium sulfate precipitation improved the purity somewhat, but further work is required to obtain large amounts of this reaction center in pure form. This research was supported by NSF grants SPI-81-65037 (to B.K.P.) and PCM-81-12759 (to J.P.T.). We are grateful to Merri Skrdla for helping with the electrophoretic studies, to George Feher for supplying Rps. sphaeroides R-26 reaction centers, and to Bill Dietrich for helpful discussions.
Keywords
- (Chloroflexus aurantiacus)
- Bacterial photosynthesis
- Chlorophyll-protein complex
- Reaction center
- Thermal stability
- Thermophilic bacterium
ASJC Scopus subject areas
- Biophysics
- Biochemistry
- Cell Biology