SPECTRAL CHANGES OF THE B800-850 ANTENNA COMPLEX FROM ECTOTHIORHODOSPIRA SP INDUCED BY DETERGENT AND SALT TREATMENT

We have studied the effects of the detergent lauryl dimethylamine N-ox ide and NaCl in the near infrared absorption spectra of the B800-850 a ntenna complex from Ectothiorhodospira sp. Strong spectral changes wer e induced on the BCh1850 band by the lauryl dimethylamine N-oxide cons isting of a blue shift, from 857 to 839-837 nm, and a hypochromism. No significant effects were detected on the BCh1800 band in the same con ditions. The changes were reversible after removing most of the deterg ent from the sample. Depending upon the detergent concentration in the solution, NaCl was also able to reverse the blueshift and increase th e intensity of the 850 nm band close to the native values. Moreover, w e have been able to separate both phenomena. Addition of 0.350 M NaCl after sample incubation with 0.15% (v/v) lauryl dimethylamine N-oxide for 30 min allowed a 9-10 nm redshift with no significant hyperchromis m of the lowest energy band. We explained the overall effect of the de tergent assuming that the lauryl dimethylamine N-oxide bound to the hy drophobic moiety of the complex and caused some protein conformational changes which affected the BCh1850 domain without affecting that of t he BCh1800. The NaCl was able to circumvent these effects, most probab ly by acting directly on the BCh1850 molecules or on the protein struc ture surrounding them.