Purification and characterization of a low molecular weight basic protein from marine turtle egg white

The egg white of marine turtle (Caretta caretta Linn.) and one species of tortoise (Geomyda trijuga trijuga Schariggar) contain a low molecular weight basic protein. It has been purified to homogeneity from the egg white of marine turtle and characterized in terms of its major physicochemical and chemical properties. The molecular weight of this protein calculated from gel filtration, sodium dodecyl sulfate-gel electrophoresis in the presence of urea, sedimentation-diffusion data, and amino acid composition is 4300. Its isoelectric point is at pH 11.1 and intrinsic viscosity is 0.038 dl g-1 in 0.2 M NaCl. It has a Stokes radius of 12.6 A and a diffusion coefficient of 16.50 x 10(-7) cm2 s-1. Analysis of the far-ultraviolet circular dichroic spectrum has shown that the basic protein contains 27% beta-pleated sheet and little or no alpha-helix. It possesses a single polypeptide chain of 40 amino acid residues with three disulfide bonds. It lacks serine, methionine, phenylalanine and carbohydrate moiety. It binds to DNA and stimulates ATPase activity due to its strong basicity. The complex of DNA-basis protein is partially resistant to the action of DNase.