Chemical properties of a high molecular weight spleen extract with permeability activity

The extract of proteins from spleen (SPF) described in the foregoing paper has been subjected to chromatographic and electrophoretic separation procedures. Although different protein fractions are obtained, most possess considerable permeability activity and no localisation of activity has been observed. Treatment of SPF with chemical reagents to modify certain amino acid side chain residues shows that primary amino groups are essential for activity. Conversion of carboxylate groups to electroneutral derivatives results in an increase in the specific activity of SPF. It is proposed that permeability activity, as observed in SPF and protein fractions derived therefrom, probably resides in certain features of primary structure which are shared by different proteins.