A Study on the Calcium Linkage of αs1-Casein in Urea Solution

Abstract

In order to study the formation of calcium cross-linkage of ケ_s1-casein, interaction of ケ_s1-casein with calcium was investigated in 4 m urea. Two types of calcium binding above and below 5 mm Ca²⁺ were found from the analysis of calcium binding curve of ケ_s1-casein in 4 m urea. Until 5 mm Ca²⁺ where the first type of binding proceeded, increase of s_20,w took place. However, the ケ_s1-casein in 4 m urea existed as a monomer even in the presence of 10 mm Ca²⁺. Since partial specific volume and molecular weight of ケ_s1-casein did not change by calcium, the increase of s_20,w is considered to be due to the change of gross structure by the formation of intramolecular cross-linkage. This cross-linkage is expected to be formed in the absence of urea, and to play an important role in the formation of the aggregates.