Comparative immunochemistry of bacterial, algal and plant ferredoxins.

1. Antibodies were produced in rabbits to the 4Fe-4S ferrodoxins from Bacillus stearothermophilus, the 2 [4Fe-4S] ferredoxin from Clostridium pasteurianum, and the 2Fe-2S ferredoxins from the blue-green algia Spirulina maxima, the green alga Scenedesmus obliquus, and the higher plant Beta vulgaris. The antibodies were tested for immunoprecipitation activity with seven bacterial, twelve blue-green algal, six eukaryotic algal and six higher plant ferredoxins. 2. Antibodies to the bacterial ferredoxins reacted to a significant extent only with their homologous proteins. On the other hand, antibodies to the plant and algal ferredoxins showed cross-reaction with other ferredoxins. There was a correlation between the degrees of immunoprecipitation and the similarity in amino acid sequences. These results suggest that the method can be used as a marker in taxonomic studies. 3. The interaction of the antibodies with the five native ferredoxins was compared with the reactions with their apoproteins. In each case the degree of interaction was different. This behaviour was interpreted as due to an influence of tertiary structure on the antibody-antigen interaction.