Abstract
Until 1993, Chl a had been believed to be essential in oxygenic photosynthesis without exception. However, Chl d is found to be dominant in a unique cyanobacterium Acaryochloris marina. From the molecular structure of Chl d, Chl d is expected to be oxidatively biosynthesized from Chl a, like Chl b. However, the biosynthetic pathway of Chl d in A. marina is not clear. The conversion of Chl a to Chl d requires an oxidative cleavage of the C=C double bond of a vinyl group of Chl a at ring I (-CH=CH2 into -CHO). We serendipitously came across the formation of Chl d from Chl a by papain in organic solvents containing water. Recently, we found that the novel conversion happened when Chl a was incubated with extracts of several vegetables. Here, we will report the Chl a to Chl d conversion catalyzed by extracts of several microalgae in aqueous acetone. The findings suggest that the conversion of Chl a into Chl d is one of the degradation reactions of Chl a in vitro, like pheophytinization and epimerization, and that the conversion may not be a rare event in nature. Our findings will provide new insight into the unsolved question as to the birth of Chl d.
