Abstract
The first half of biosynthetic pathway of chlorophylls (Chl) from glutamate to protoporphyrin is shared with heme biosynthesis. Mg-chelatase, a three-subunit enzyme (ChlI, ChlD and ChlH), catalyzes the insertion of Mg2+ into protoporphyrin, the first reaction of Mg-branch. Thus, it is suggested that Mg-chelatase plays an important role in the teterapyrrole allocation mechanism. A single recombinant mutant A5101 was isolated from the cyanobacterium Plectonema boryanum in a trial to isolate a chlD-disruptant. Absorption spectrum of dark-grown A5101 cells suggested significant decrease in the Chl and phycobiliproteins contents. The Chl content of A5101 was 12 % of the wild type. While A5101 grew slightly faster than the wild type in darkness, A5101 did not grow under photoautotrophic conditions. Further phenotypic analysis such as the contents of some proteins of photosystems and Chl biosynthesis will be presented and the function of ChlD is also discussed.
