Kinetic analysis of demetalation of bacteriochlorophyll c and e homologs purified from green sulfur photosynthetic bacteria

Substituent-dependent demetalation kinetics of natural bacteriochlorophyll (BChl) c and e homologs purified from two green sulfur photosynthetic bacteria was first studied. Separated BChl e homologs, which possessed a formyl group at the 7-position of their chlorin macrocycles, exhibited a significantly slow removal of central magnesium to free-base bacteriopheophytins in acidic aqueous acetone compared with the corresponding BChl c homologs, which possessed a methyl group at the 7-position. Additional methyl groups at the 82-position of both BChl c and e molecules had little effect on the demetalation kinetics.