Abstract
K-Casein and αs1-K-casein complex with a weight ratio of unity were dissolved in 50mM cacodylate-HCl-70mM KCl buffer containing 0.02% of sodium azide (pH 7.1), and their size and shape in the absence and/or presence of calcium ions were observed with the electron microscope. In the absence of calcium ions, both K-casein and αs1-K-casein complex were spherical particles. However, the mean length of αs1-K-casein complex (12nm) was smaller than that of K-casein (17nm), which suggested that complex formation led to dissociation of the K-casein polymer. The addition of calcium ions to the complex led to the formation of bent chains, though micelle-like aggregates were not observed even at 20mM calcium. Comparison of the frequency distributions of αs1-K-casein complex at 0, 5, 10, 15 and 20mM of calcium with the calculated probability distributions suggested that most αs1-K-casein complexes had two binding sites above 10mM of calcium, which seemed to be essential for the stability of casein micelle.
