Abstract
Chlorin ring structure of chlorophyll a is formed by the reduction of porphyrin D-ring by light-independent protochlorophyllide reductase, a nitrogenase-like enzyme, in most photosynthetic organisms. Bacteriochlorophyll a has bacteriochlorin ring structure that is formed by the reduction of chlorin B-ring. Phenotypic analysis of mutants indicated that the three genes, bchX, bchY and bchZ, which show similarity to those of structural genes of nitrogenase, are involved in the chlorin B-ring reduction. However, there has been no biochemical evidence. We tried to reconstitute the chlorin B-ring reduction with purified proteins. BchX was purified as a single polypeptide, and BchZ was co-purified with BchY. When both components, BchX and BchY-BchZ, were incubated with chlorophyllide a, ATP, ATP-regeneration system and dithionite under anaerobic conditions, chlorophyllide a was converted to a new pigment with longer wavelength. Involvement of second nitrogenase-like enzyme in bacteriochlorophyll biosynthesis will be discussed.
