Spinach chloroplast thioredoxins in evolutionary drift.

The amino acid sequences surrounding the active sites of spinach chloroplast thioredoxins m and f have been determined. Both types of thioredoxins share common ancestor genes with the E. coli one, demonstrated by invariant active site sequences. The m-type thioredoxins have closer homology with the E. coli one in the sequence analyzed as well as in enzymatic specificity, whereas the f-type is less homologous both in sequence and specificity. It suggests that the m-type gene represents a prototype conserved throughout evolutionary processes whereas the f-type has undergone mutations resulting in a modified specificity.