Crystallization with hapten of the Fab' fragment from a mouse IgA myeloma protein with antidinitrophenyl activity.

Protein 315, a mouse myeloma IgA protein which binds nitrophenyl ligands, and its pepsin-produced Fab’ fragment have been purified by affinity chromatography. The Fab’ fragments were found to be homogeneous by polyacrylamide electrophoresis and isoelectric focusing, and to possess a uniform binding constant. These fragments were readily crystallizable at low salt concentration near their isoelectric point (pH 4.7). Similarly crystals can be obtained of the Fab’-hapten complex. Such crystals have a 1: 1 molar ratio of hapten (t , N-dinitrophenyl lysine) to protein.