Human Secretory Component

The gel filtration behavior of purified secretory component indicated an Einstein‐Stokes radius of 44 to 46 Å, a diffusion coefficient of 4.7 to 4.9 × 10−7 cm2 sec−1, and a molecular weight of about 110,000 daltons Ultraccntrifugation indicated a sedimentation coefficient of 4.8 to 5.4S and a molecular weight of about 83,000 daltons. The latter estimate was based on a partial specific volume of 0.712 ml/g, calculated from the amino acid and carbohydrate composition Isoelectric focusing demonstrated at least six fractions with pi ranging from pH 4.75 to 5.25. Different fractions were, apparently, antigenically similar and complexed spontaneously with dimeric IgA and 19S IgM. This completing was of slightly higher efficiency for secretory component enriched in the more basic material