Evolutionary information involved in primary structures of chloroplast-type ferredoxins

The complete amino acid sequence of a chloroplast-type ferredoxin from a fresh water prokaryote, Aphanothece sacrum, was determined. The sequence consisted of 96 amino acid residues and was homologous to those of ferredoxins of higher plants. Comparison of eight ferredoxins, including one from a green alga and three from blue-green algae, suggested that the sequences of algal ferredoxins were as different from one another as from those of higher plants. The relationship between the numbers of differences in amino acids and the period since separation from a common ancestor was not linear, even after correction for multiple substitution at an amino acid site in the sequence. It is very likely that the ferredoxins of angiosperms evolved rather rapidly and that those of algae, and particularly blue-green algae evolved rather slowly in the evolutionary scale. Several possible mechanisms of evolution of plants are discussed.