PRIMARY STRUCTURE OF A MYOHEMERYTHRIN-LIKE CADMIUM-BINDING PROTEIN, ISOLATED FROM A TERRESTRIAL ANNELID OLIGOCHAETE

Two isoforms of a cadmium-binding protein (Cd-BP 14a and Cd-BP 14b) we re isolated from the terrestrial oligochaete annelid, Allolobophora ca liginosa The complete amino acid sequence of the major isoform Cd-BP 1 4a (molecular mass: 13441 Da; 119 residues) and the amino-terminal seq uence (57 residues) of Cd-BP 146 were determined. The sequence of Cd-B P 14a is highly similar to that of myohemerythrins present in marine i nvertebrates. Furthermore, as myohemerythrins, Cd-BP 14d and Cd-BP 146 bind two atoms of iron and their ultraviolet/visible spectra are typi cal of non-heme iron-binding proteins. Three substitutions were found in the amino-terminal half of the proteins at positions 19, 21 and 41. The substitutions at positions 13 and 21 are conservative, whereas th at at position 41 consists of the replacement of an aspartate residue in isoform a by a lysine residue in isoform b. To our knowledge, it is the first report of a protein belonging invertebrate.