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Diastereoselective Control of Bacteriochlorophyll e Aggregation. 3-S-BChl e Is Essential for the Formation of Chlorosome-Like Aggregates

2000; American Chemical Society; Volume: 104; Issue: 44 Linguagem: Inglês

10.1021/jp0013356

1520-6106

Dorte B. Steensgaard, Hainer Wackerbarth, Peter Hildebrandt, Alfred R. Holzwarth,

Algal biology and biofuel production

We have investigated supramolecular bacteriochlorophyll (BChl) e aggregates in four different solvent systems. Aggregates of HPLC-purified BChl e species, 31-R-8-ethyl-12-ethyl BChl e, 31-R-8-propyl-12 ethyl BChl e, 31-S-8-propyl-12-ethyl BChl e, and 31-S-8-isobutyl-12-ethyl BChl e, in cyclohexane, n-hexane, H2O/monogalactosyldiglyceride, or H2O/lecithin, indicate two different aggregate structures, as judged from absorption, circular dichroism, infrared, and resonance Raman spectroscopies. Aggregates of 31-R-BChl (R-BChl) e were characterized by a 706 nm absorption band and broad C-131 carbonyl stretching bands at 1650−1680 cm-1. In contrast, aggregates of 31-S-BChl (S-BChl) e displayed a Qy band maximum at 717 nm and a carbonyl stretching band at 1650 cm-1 only. All measurements indicated that the aggregates of S-8-isobutyl-12-ethyl BChl (S[IE]BChl) e mimicked the supramolecular aggregates in intact chlorosomes of Chlorobium phaeobacteroides much better than did the R-8-ethyl-12-ethyl BChl (R[EE]BChl) e-type aggregate. However, when mixtures of R[EE]BChl e and S[IE]BChl e were used for aggregate formation, even small amounts of S[IE]BChl e were sufficient to cause the formation of chlorosome-like aggregates. We conclude that S-BChl e is essential for the formation of chlorosome-like aggregates. Finally, we describe a refined model for the supramolecular chlorosomal aggregate structure.