Effect of Chemical and Enzymatic Radioiodination on in Vitro Human Clq Activities

Abstract

Conditions are described whereby human Clq may be enzymatically radioiodinated with full retention of hemolytic activity. A comparison is made between the chloramine T (CT) and lactoperoxidase (LP) methods of iodination which indicates the following: 1) Clq may be iodinated to a level of 0.2 atoms iodine/molecule by using LP with no detectable loss in hemolytic activity, whereas, at a level of 0.02 atoms incorporated/molecule with CT, Clq is only 50% active. Thus the hemolytic activity of Clq is quite labile to either low levels of iodide incorporation or the oxidizing conditions of the labeling procedure. 2) Its ability to bind immune complexes, conversely, is virtually resistant to the levels and conditions of iodination reported here. 3) With either labeling method, iodide is incorporated exclusively into only the smallest of the three covalently bonded subunits.