G-Man (Half-Life) refers to simply as his "employers". His mysterious nature has made him an icon of the "Half-Life" series, with his identity and motives remaining almost completely unexplained. The G-Man's name comes from "G-Man", an American colloquialism meaning "Government Man". However, within the "Half-Life" games, he is identified by this name only in the program code and the multiplayer profile menu as a default name option, not within the story itself; his name is derived from his "Half-Life" model and entity name and has since been reused in subsequent games of the series. His name has been confirmed and he has
Protein A/G a lesser extent) IgD. Protein A/G also binds to all subclasses of mouse IgG but does not bind mouse IgA, IgM or serum albumin. This allows Protein A/G to be used for purification and detection of mouse monoclonal IgG antibodies, without interference from IgA, IgM and serum albumin. Mouse monoclonal antibodies commonly have a stronger affinity to the chimeric Protein A/G than to either Protein A or Protein G. Protein A/G also has been used for purification of macaque IgG. In addition to Protein A/G, other immunoglobulin-binding bacterial proteins such as Protein A, Protein G and Protein L are all