Aggregation of chlorophyll a probed by resonance light scattering spectroscopy.
We report the resonance light scattering (RLS) spectra of chlorophyll a aggregated in a 9:1 solution of formamide and pH 6.8 phosphate buffer. The aggregate formed after 2 h of mixing, referred to as Chl469, shows a strong scattering feature at 469 nm (Soret band) and a much weaker feature at 699 nm (Qy band). A kinetic investigation confirmed that the aggregation process is cooperative, and also detected one intermediate (Chl458) with a strong RLS spectrum but only a weak CD spectrum. We propose that aggregation proceeds via at least three steps: 1) formation of a nucleating species, probably a dimer of chlorophylls; 2) formation of large aggregates with little or no secondary structure (e.g., Chl458); and 3) conformational change to form helical aggregate (Chl469).
de Paula
J C
JC
Department of Chemistry, Haverford College, Pennsylvania 19041.
Robblee
J H
JH
Pasternack
R F
RF
D055592:Biophysical Phenomena; D001703:Biophysics; D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D002942:Circular Dichroism; D005559:Formamides; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D008968:Molecular Conformation; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D012996:Solutions; D013053:Spectrophotometry / Q000379:methods / Q000706:statistics & numerical data; D014867:Water
D005559:Formamides; D012996:Solutions; D014867:Water; D002734:Chlorophyll; C031066:formamide; D000077194:Chlorophyll A