Conformational differences between latent and active plasminogen activator inhibitor, PAI-1: a spectroscopic study.

The protein conformation of latent and active PAI-1 has been studied with circular dichroism, absorbance and fluorescence spectroscopy. The far ultraviolet circular dichroism spectrum of latent PAI-1 displays a more negative band at 220 nm than active PAI-1, crossing the baseline at a lower wavelength. Active PAI-1 shows an absorption maximum at lower wavelength (269 nm) than present in latent PAI-1 (278 nm). In consistency, slow denaturation of active PAI-1 by incubation for two hours at 37 degrees C induces a shift in the absorption maximum from 268 nm to 274 nm. The fluorescence emission maximum of latent PAI-1 is at lower wavelength (335 nm) than that of active PAI-1 (340 nm). These spectroscopic differences are interpreted as reflecting a more tight conformation, with the tryptophan residues in a more apolar environment, in latent PAI-1 compared to active PAI-1.