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Effect of Certain Divalent Cations on the Dye-Binding Capacities of Casein and Milk¹

Department of Animal Science

L. Watkins

Department of Biology, Tennessee A & I State University, Nashville

J. Ross

Department of Biology, Jackson State College, Jackson, Mississippi

ABSTRACT

Klotz (2, 4) developed a theory to predict dye-binding by proteins, which considered the intramolecular interactions between carboxyl, hydroxyl, and basic nitrogen groups. He proposed that the carboxyl and hydroxyl groups preferentially formed hydrogen bonds with each other and only the surplus carboxyl or hydroxyl groups left over from this interaction were free to interact with the cationic nitrogen groups. The remaining cationic nitrogen centers are then available to an attacking dye anion. The bond energies of these interactions support his position (2).

As a logical consequence of Klotz' postulate, it is reasonable to propose that increased dye-binding would occur if a suitable agent were introduced to break the intramolecular bonds, specifically the carboxyl-cationic nitrogen or hydroxyl-cationic nitrogen bonds. This communication reports the use of some metallic ions to obtain an increase in dye-binding- capacity of milk and casein.

Casein sols or milk were treated with reagent grade metallic salts or their 1 m solutions (hydroxides, chlorides, or sulfates), such that the metal ion concentrations were from 0 to 0.5 M.

¹ A portion of this work was supported by the National Science Foundation through their Undergraduate Besearch Participation Program by support of Mr. Watkins and Mr. Boss. A portion was also taken from the Senior Project of Terry Bynum, in partial fulfillment of the requirements for the Bachelor of Science Degree in Biochemistry.

² Present address: Dept. Dairy and Food Industry, Iowa State University, Ames.

³ Present address: Florence, Alabama.