The kinetics of the reaction between the blood-group antibody anti-c and erythrocytes

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Abstract
The kinetics of the association between the red-cell antibody anti-c and the corresponding antigen on the red cell were investigated. The non-specific uptake of I131 by red cells from iodinated antiserum was reduced by competitive inhibition with unlabelled serum proteins; further reduction was made by extraction of the red cells with lipid solvents, which removes I-131 labelled lipids and [I131 ] iodide. Two estimates were made of the relationship between antibody titer and antibody concentration; thus a titer of 256 corresponded to a concentration of 0.13 [mu]M (21 [mu]g/ml) and a.titer of 128 corresponded to a concentration of 0.087 [mu]M.(14 [mu]g/ml). The number of c antigen sites on each red cell was estimated to be 65,000. The reaction between antibody and antigen was reversible and heterogeneous with respect to its equilibrium constant. The minimum range of the association constants was K 1.9 x 107 - 1.8 x 108 l.mole-1 The values of the thermodynamic constants were standard free energy change,/[DELTA] F0 = 10.1 to 11.3 kcal./mole; standard enthalpy change, [DELTA]H0 = - 1.5 [plus or minus] 0.6 kcal./mole; standard entropy change, [DELTA] So = 28 cal./ degree/mole.