Exclusive Occurrence of k Chains in Isolated Cold Haemagglutinins

All of 37 cold haemagglutinins isolated from sera of patients with chronic cold haemagglutinin syndrome were shown to contain k chains only. When data obtained from other investigators are added, it appears that a total of at least 59 isolated cold haemagglutinins have been found to contain only type K γM‐globulin molecules. In analogy with current views on the structure of the γG‐globulin molecule, it is suggested that each active site of the cold haemagglutinin molecules is made up by a close interaction of the heavy and light polypeptide chains. It is further suggested that the characteristic behaviour of cold haemagglutinins with regard to serological specificity and/or thermal amplitude is only compatible with relatively small structural variations of the light chains within the limits imposed by k chains.