DIVISION OF BIOPHYSICS: DIVERSE APPLICATIONS OF ISOTOPICALLY LABELED INSULIN*

INSULIN ANTIBODY VARIATIONS IN RABBITS AND GUINEA PIGS AND MULTIPLE ANTIGENIC DETERMINANTS ON INSULIN

1. A method is presented for measuring the degree to which insulin antibodies in one antiserum react with an insoluble insulin complex saturated with antibodies from a different antiserum. 2. Many rabbits produce antibodies which bind to portions of the insulin molecule to which antibodies from guinea pigs or other rabbits cannot bind. 3. Occasional guinea pigs produce antibodies which bind to portions of the insulin molecule to which antibodies from rabbits or other guinea pigs cannot bind. 4. Studies with labeled antisera and repeated incubations of test antisera with antibody insulin complexes demonstrate the individual antibody variations to be due to antibodies directed to different determinants and not to dissociation of antibodies from the same determinant on the insulin molecule. 5. More than one antibody molecule can simultaneously bind to an insulin molecule. 6. Insulin has a multiplicity of antigenic determinants. 7. The relationship between antigenic determinants, insulin antibodies, and neutralization of insulin by antisera is discussed. 8. The determinants to which insulin antibodies are directed appear to be characteristic for the individual rabbit or guinea pig immunized. It is postulated therefore that genetic factors direct antibody production toward specific determinants when insulin is the antigen.

Distribution of free and antibody-bound peptide hormones in two-phase aqueous polymer systems

Peptide hormones labelled with radioactive iodine were partitioned into the aqueous two-phase polymer systems developed by Albertsson (1960) and the conditions required for separation of free from antibody-bound hormone have been worked out. Hormones studied included insulin, growth hormone, parathyroid hormone and [arginine]-vasopressin. Free and antibody-bound hormones show different distribution coefficients in a number of systems tested; two systems, the dextran-polyethylene glycol and dextran sulphate-polyethylene glycol system, give optimum separation. Free hormones distribute readily into the upper phase of these systems, whereas hormone-antibody complexes, as well as uncombined antibody, are found almost completely in the lower phase. Various factors including the polymer concentration, the ionic composition of the system, the nature of the hormone and the nature of added serum protein differentially affect the distribution coefficients for free and antibody-bound hormone. These factors can be adequately controlled so as to improve separation. The two-phase partition method has been successfully applied to measure binding of labelled hormone to antibody under standard radioimmunoassay conditions. It exhibits several advantages over the method of equilibration dialysis and can be applied to the study of non-immunological interactions.