protein l was first isolated from the surface of bacterial species "peptostreptococcus magnus" and was found to bind immunoglobulins through l chain interaction, from which the name was suggested. it consists of 719 amino acid residues. the molecular weight of protein l purified from the cell walls of "peptostreptoccus magnus" was first estimated as 95kd by sds-page in the presence of reducing agent 2-mercaptoethanol, while the molecular weight was determined to 76kd by gel chromotography in the presence of 6 m guanidine hcl. protein l does not contain any interchain disulfide loops, nor does it consist of disulfide-linked subunits. it is an acidic molecule with a pi of 4.0. unlike protein a and protein g, which bind to the fc region of immunoglobulins (antibodies), protein l binds antibodies through light chain interactions. since no part of the heavy chain is involved in the binding interaction, protein l binds a wider range of antibody classes than protein a or g. protein l binds to representatives of all antibody classes, including igg, igm, iga, ige and igd. single chain variable fragments (scfv) and fab fragments also bind to protein l.