Fluorescence Polarization of αs1, κ-Caseins and αs1-κ-Casein Complex

Abstract

Conjugates of αs1-,κ-caseins and αs1-,κ-casein complex were prepared with dimethylaminonaphthalenesulfonate and pyrenebutyrate. Their fluorescence lifetimes and the rotational relaxation times were measured by single photon counting technique and fluorescence depolarization technique, respectively. Both dimethylaminonaphthalenesulfonate and pyrenebutyrate conjugates had more than two lifetimes and the longer lifetime of pyrenebutyrate conjugates was near 140 nsec. The rotational relaxation time of pyrenebutyrate αs1-,κ-casein complex was smaller than that of pyrenebutyrate κ-casein polymer, which suggested that the complex formation of αs1- and κ-casein polymers led to dissociation of the κ-casein polymer. Changes of the rotational relaxation time as a function of weight ratio of αs1- and κ-casein polymers (αs1/κ) showed the specific variation and it was suggested that 4 moles of αs1-κ-casein complex were formed from one mole of κ-casein polymer.