Abstract
Coproporphyrinogen III oxidase (CPO) catalyzes the oxidative decarboxylation of coproporphyrinogen III to form protoporphyrinogen IX in heme biosynthesis that is shared with the chlorophyll biosynthesis in photosynthetic organisms. There are two structurally unrelated CPOs; oxygen-dependent (HemF) and oxygen-independent (HemN) oxidases. The cyanobacterium Synechocystis sp. PCC 6803 has one hemF-like gene, sll1185, and two hemN-like genes, sll1876 and sll1917. To address how the different types of CPO operate in the environments under oxygen-fluctuated environments, three mutants lacking one of the three genes were isolated. The Δsll1185 mutant failed to grow under aerobic conditions with anomalous accumulation of coproporphyrin III. The Δsll1876 mutant grew much slower than wild-type under micro-oxic conditions and the coproporphyrin III accumulation was induced by 5-aminolevulinate feeding. In contrast, Δsll1917 grew as well as wild-type. These results suggested that Sll1185 and Sll1876 operate as the dominant CPO under aerobic and micro-oxic conditions, respectively.
