DOES THE B820 SUBCOMPLEX OF THE B880 COMPLEX RETAIN CAROTENOIDS

A study is reported on the modification of the B880-RC assembly of Chr omatium minutissimum during -glucopyranoside/dodecyl-beta-D-maltoside/ Deriphat polyacrylamide gel electrophoresis followed by electroelution with dodecyl-B-D-maltoside and high performance liquid chromatography with octyl-B-D-glucopyranoside according to the method developed by K erfeld et al. (Biochim. Biophys. Acta 1185, 193-202 [1994a]) for isola tion of the B820 subcomplexes of Chromatium purpuratum. The B880-RC as sembly of Chromatium minutissimum isolated by electrophoresis was cont aminated by the B800-850 complex. It was further separated into four c omponents, three of which were in agreement with the cited work: (i) c olorless contaminations, (ii) the B880-RC assembly, (iii) the B800-850 complex. In contrast with Kerfeld et al. (1994a), the fourth band was a band of free pigments (Bchl or Bchl+carotenoids) which had the same molecular mass as the B820 subcomplex of Chromatium purpuratum. For c omparison, the B880-RC enriched fraction of Rhodospirillum rubrum modi fied by lyophilization in the presence of octyl-B-D-glucopyranoside wi th or without carotenoids was separated by high performance liquid chr omatography with octyl-beta-D-glucopyranoside. The apparent molecular mass of the B820 subcomplex was 30 kDa for the sample without caroteno ids and 245 kDa for that with carotenoids. The common principles of or ganization of the B880 complex, the interaction of the B800-850 comple x with the B880-RC assembly, the participation of carotenoids in the s tabilization of the B880 complex structure and the ability of differen t isolation steps to modify the structure of the B880 complex are disc ussed. It was concluded that there are other explanations for the pres ence of carotenoids in the B820 subcomplex. Hence, the question of whe ther the B820 subcomplex retains carotenoids remains open.