FIGURE 3.

Binding studies on the Biacore 2000 instrument. Binding of HIV-1 gp120, b121a and b122a to surface-immobilized IgGb12 and b6 was monitored by SPR. A, curves 1, 2, 3, and 4, 50, 100, 150, and 200 nm concentrations of gp120 analyte, respectively. B, curves 1, 2, and 3, 78, 117, and 157 μm concentrations of b121a, respectively. C, curves 1, 2, 3, and 4, 8.5, 17, 34, and 51 μm concentrations of b122a, respectively. Curve 5, reduced and carboxymethylated b122a, which did not show any measurable binding to b12. D, curves 1 and 2, 100 nm full-length gp120 and 20 μm b122a. Surface density of both antibodies was 900 resonance units (RU); buffer was PBS, pH 7.4, 0.005% P20; and flow rate was 30 μl/min. The fact that b122a loses binding upon reduction and carboxymethylation of its cysteines shows that the binding is specific. b122a also does not show any binding to b6. Binding parameters are listed in Table 1.