Résumé
In the tetraploid amphibian Odontophrynus americans the selective precipitation of vitellogenin by Mg2+ from plasma treated with ethylene diaminetetraacetic acid (EDTA) or ethylene bis (oxyethylenenitrilo)-tetraacetic acid (EGTA) is a pH-dependent phenomenon. Utilizing sucrose gradient centrifugation of whole plasma we have shown that under standardconditions (pH 7.0) the estimated apparent sedimentation coefficient of vitellogenin is 17s.At pH 8.0 and in the presence of EDTA or EGTA there is a decrease of the vitellogenin sedimentation coefficient.This behavior is restricted to vitellogenin as othewr plasma proteins show no alteration in their sedimentation coefficient after similar treatment. The treatment with EDTA at pH 8.0 also induces changes in the vitellogenin molecule which can be detected by partial proteolysis with chymotripsin A