Formation of Clay‐Protein Complexes

Abstract Proteins (catalase, α‐casein, α‐chymotrypsin, edestin, β‐lactoglobulin, lysozyme, ovalbumin, ovomucoid, and pepsin), ranging in molecular weight from approximately 17,000 to 310,000 and in isoelectric point from approximately pH 2 to 11, were adsorbed onto smectite homoionic to H, Na, Ca, Al, La, or Th. Adsorption was observed in every combination of homoionic clay and protein, even when the ambient pH of the clay suspensions (which ranged from approximately pH 3 to 7) was several units above the isoelectric point of the protein. The amount of protein adsorbed and the shapes of both the adsorption isotherms (measured by loss of protein from solution) and the binding isotherms (retention against ultimate washing with glass distilled water) were more related to the molecular weight of the proteins and to the valency of the cations on the clay exchange complex than to the ambient pH of the clay‐protein systems and the isoelectric point of the proteins. In general, the amount of adsorption was directly proportional to molecular weight of the proteins and inversely proportional to cationic valance.