Chemical Nature of Component Involved in the Reaction Between Iodine and Complement

Abstract

Chow and Wong have reported 1 that iodine destroys the complement activity of normal sera and that there exists a definite stoichiometric relationship between the amounts of iodine used and complement inactivated. It seemed to be of interest to find out the chemical nature of and the component involved in this process. This may either be an addition of iodine to ethylenic linkages or replacement of hydrogen atoms attached to the carbon atoms, with the result that iodine will be bound to complement. It may also be a simple oxidation of complement by iodine, which in turn, is reduced to free unbound iodide. In order to arrive at some conclusion, we have determined quantitatively first the bound iodine, if any, to the inactivated serum protein, and secondly, the free iodine in the mixture. The present communication gives the result of such a study.

1. Determination of non-dialyzable organic iodide in the inactivated serum protein. To 50 cc of fresh hog serum (having a titer of 21 units per cc) were added 10 to 15 cc of N/10 iodine solution. One-half cc of the resulting solution was found to contain less than one unit of complement per cc. Therefore, the inactivation of complement was almost complete. The inactivated hog serum was dialyzed in a collodion tube of small porosity against distilled water at 0°C until free from iodide. Five cc of N/10 sulphuric acid were added to effect a complete solution of the protein that was precipitated out during dialysis. The total volume was then made up to 100 cc with water, i. e., two times the original volume. Three 20 cc samples were pipetted into separate nickel crucibles, and their iodine content determined according to the method of McCullagh. 2 The results are given in Table I.

2. Determination of iodide in the protein-free filtrate. A typical experiment was as follows : One cc of fresh hog serum (titer of 33 units per cc) was diluted ten fold with 0.85% sodium chloride solution. To each of four 2.0 cc samples of the diluted hog serum were added 5 cc of N/10 iodine solution in distilled water. To one of the mixtures, 0.6 cc of 10% sodium chloride solution was added to make the solution isotonic, in order to determine the percentage of complement activity destroyed by this amount of iodine. To the other three was added 1 cc of 2/3 N sulphuric acid and 1 cc of 10% sodium tungstate solution. The suspensions were centrifuged and 4 cc of the supernatant were used for the determination of iodide, in the usual manner, by oxidizing it to iodate with bromine. The results of several such experiments with the sera of different species of animals are given in Table II.