Physicochemical studies of demetalation of light-harvesting bacteriochlorophyll isomers purified from green sulfur photosynthetic bacteria.
Demetalation kinetics of bacteriochlorophylls (BChls) c, d and e from green sulfur photosynthetic bacteria were studied under weakly acidic conditions. Demetalation rate constants of BChl e possessing a formyl group at the 7-position were significantly smaller than those of BChls c and d, which had a methyl group at this position. The activation energy of demetalation of 3(1)R-8,12-diethyl([E,E])-BChl e was 1.5-times larger than that of 3(1)R-[E,E]-BChl c. 15N-labeled 3(1)R-[E,E]-BChls c and e were purified from cells of green sulfur bacteria grown in a medium containing 15NH4Cl, and their 15N NMR spectra were measured. The chemical shifts of N21, N22 and N23 atoms of 3(1)R-[E,E]-BChl e were lower-field shifted than those of 3(1)R-[E,E]-BChl c, respectively, and especially the difference in chemical shifts of N22 was significantly large. These results suggest that the electron-withdrawing formyl group at the 7-position of BChl e affected an electronic state of the chlorin macrocycle and caused BChl e to be more tolerant for removal of the central magnesium compared with BChls c and d.
Hirai
Yuki
Y
Department of Chemistry, Faculty of Science and Engineering, Kinki University, Higashi-Osaka, Osaka, Japan.
Tamiaki
Hitoshi
H
Kashimura
Shigenori
S
Saga
Yoshitaka
Y
D001429:Bacteriochlorophylls / Q000378:metabolism*; D041883:Chlorobium / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003470:Culture Media; D007536:Isomerism; D007700:Kinetics; D008670:Metals / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D013696:Temperature
D001429:Bacteriochlorophylls; D003470:Culture Media; D008670:Metals