Hydrophobic surface areas and net charges of αs1-, κ-casein and αs1-casein: κ-casein complex

Abstract

Summary: Hydrophobic surface areas of α_s1- and κ-casein polymers and α_s1-casein: κ-casein complex were estimated by the salting-out technique using various salts according to the theory of Melander & Horvath (1977). Calculated hydrophobic surface areas of α_s1, κ-casein polymers and α_s1-casein: κ-casein complex were 1976, 3571 and 2989 Ų respectively. Assuming that κ-casein polymer dissociated into 4 particles in complex formation and that 1 mole of α_s1-casein: κ-casein complex was produced from 2 mole of α_s1-casein polymer and one of these dissociated κ-casein particles, the hydrophobic surface area of α_s1-casein: κ-casein complex was less than those of 2 mole of α_s1-casein polymer plus a quarter κ-casein polymer. On the other hand, the net charge of α_s1-casein: κ-casein complex was nearly equal to that of 2 mole of α_s1-casein polymer plus a quarter of κ-casein polymer. From these results, it was concluded that the complex formation of α_s1- and κ-casein polymers was hydrophobic and that electrostatic interaction did not participate in complex formation.