PA inhibition constant for gp120-to-CD4 complex formation.

<p>Inhibition of gp120-CD4 complex formation was investigated by gp120 capture ELISA. Envelope gp120 (IIIB) protein was captured on 96 well flat bottom plates, washed, and incubated in the presence of CD4-biotin alone or in the presence of increasing concentrations of PA, as indicated. Strepavidin-HRP was added, and then developed by addition of o-Phenylenediamine dihydrochloride (OPD) substrate. Colorimetric reaction was stopped by adding 1 N HCl, and read at 490 nm. % CD4 binding was calculated from gp120-CD4 complex formation in the absence of PA inhibitor, and inhibition constant, K_i, was calculated utilizing previously published equation <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0024803#pone.0024803-Cheng1" target="_blank">[18]</a>. Representative of three experiments, all data are mean ± SD.