As an effort to elucidate the quaternary structure of cyclomaltodextrinase I-5 (CDase I-5) as a function of pH and salt concentration, the dissoci-ation/association processes of the enzyme were investigated under various pH and salt conditions. Previous crystallographic analysis of CDase I-5 indicated that it existed exclusively as a dodecamer at pH , forming an assembly of six 3D domain-swapped dimeric subunits.