Dimerization kinetics of the IgE-class antibodies by divalent haptens. II. The interactions between intact IgE and haptens.

Interactions between a monoclonal, DNP-specific IgE molecules (hybridoma A2) and divalent DNP-haptens in solution cause aggregation of the former predominantly into closed rings of two IgE and two divalent haptens (Schweitzer-Stenner, R., A. Licht, I. Lüscher, and I. Pecht. 1987. Biochemistry. 26:3602-3612). The time course of this process was now investigated by titrating the A2-IgE with divalent DNP-haptens having long and rigid oligoproline spacers (di(N epsilon-2,4-dinitrophenyl)-6-amino-hexanoate-aspartyl-(prolyl)n-L-ly- syl; n = 24, 27, 33). Binding was expressed in quenching of the IgE intrinsic tryptophan emission. As shown in the preceding paper, hapten addition to the IgE-A2 at rates faster than a distinct threshold value led to nonequilibrium titrations (NETs) from which kinetic processes slower than 2 s-1 can be resolved. Analysis of these titrations shows that the dimeric rings open at rates of approximately 10(-2) s-1, independent of the divalent hapten's spacer length. The ring closure rate, however, decreases with spacer length. The latter observation was qualitatively rationalized in terms of the diffusion process of a Gaussian chain which relates the ring closure rate constant to the expectation value for the distance between the free ends of the respective open chain.