Light Scattering Studies of α_{s1, 2}-Caseins

Light scattering studies have been carried out on α_{s1, 2}-Caseins, a preparation which accounts for 45% of the optical density of whole casein and consists of two similar components.¹³ The components exist in monomeric state at pH 12, ionic strength 0.3 to 1.2 and room temperature. Under these conditions the refractive index increment is 0.181 mi. per g. The molecular weight of protein dialyzed at pH 12 using protein concentrations above 4 mg. per ml. was found to be 27, 300 ± 1500 (95% confidence limits). The second virial coefficient was approximated by the equation B = [17 - 17T/2] × 10^-4moleml./g.². Protein dissolved directly at pH 12 gave a molecular weight of 27, 000 ± 1000. Unpredictable, usually irreversible, aggregation occurs under these conditions: (a) at ionic strengths below 0.3 at pH 12; (b) on interaction with a factor released by dialysis membranes at high pH, acting at protein concentrations below 3 mg. per ml.; (c) when a rapid pH-ionic strength increase is imposed on protein in solution at pH 7; (d) on surface denaturation caused by bubbling or foaming.