Protochlorophyllide reductase in photosynthetic prokaryotes and its role in chlorophyll synthesis.

1. DNA sequences hybridizing with the wheat protochlorophyllide reductase gene have been detected during genomic Southern blots of various cyanobacterial DNA samples. No such hybridization was observed with DNA from photosynthetic bacteria. 2. A fragment amplified from Phormidium laminosum DNA has been characterized and shown to be 73% similar to the corresponding wheat sequence. At the protein level the similarity is 91%. When used as a probe for Southern blotting the Phormidium DNA fragment confirmed the authenticity of some of the original signals obtained with the wheat probe. 3. Peptides of molecular mass 36, 30 and 60 kDa are immunodetected by a wheat reductase antibody during Western blotting of Phormidium preparations. These are purported to correspond to the cyanobacterial mature reductase protein, a stable proteolytic fragment and soluble dimeric forms of the latter respectively. 4. Adaptation of Phormidium to growth in red light (delta > 670 nm) or darkness led to no significant changes in the total level of immunodetected peptides or protochlorophyllide within the cells. 5. The specific activity of the reductase in Phormidium membranes has been tentatively estimated as 0.5 unit/mg of protein, a value comparable with that found in preparations from mature chloroplasts of higher plants.