Amino Acid Composition of Univalent Fragments of Rabbit Antibody.

Univalent fragments of gamma-globulin preparations from four individual rabbits were fractionated and the amino acid compositions of end fractions were compared. For amino acids with uncharged side chains, differences were consistently less than one residue per fragment of molecular weight 50,000. There were differences in the content of amino acids, other than glutamic acid, with charged side chains; these were in the direction expected on the basis of relative strength of adherence to carboxymethyl cellulose and electrophoretic mobility. Exclusive of any possible differences in amide, the total difference in charged groups was three to four residues per fragment. Sine the net charge of univalent fragments reflects that of the gamma-globulin molecule from which the fragments are derived, corresponding differences in composition may also exist among whole gamma-globulin molecules.