Light-independent isomerization of bacteriochlorophyll g to chlorophyll a catalyzed by weak acid in vitro

Rapid conversion of bacteriochlorophyll g (BChl g) to chlorophyll a (Chl a) was observed in acetone on addition of acid in the dark. The product, Chl a esterified with farnesol (Chl aF), was identified by liquid chromatography and fast atom bombardment mass spectrometry. Acid-catalyzed formation of 81-OH-Chl aF, a primary electron acceptor in the heliobacterial reaction center, was also observed in diethyl ether in the dark. These results suggest that acid-catalyzed isomerization is a candidate for the chemical evolution of BChl g to the more stable Chl a and that 81-OH-Chl aF can easily be synthesized from BChl g under weakly acidic conditions in the dark.