Extrinsic circular dichroism of the derivatives of bovine beta-lactoglobulin A and B with 2-chloromercuri-4,6-dinitrophenol and 2,6-dichloromercuri-4-nitrophenol
de Cuyper, M.; Prèaux, G.; Lontie, R.
Archives Internationales de Physiologie et de Biochimie 81(2): 366
1973
ISSN/ISBN: 0003-9799 PMID: 4126220 Document Number: 66565
2-Chloromercuri-4,6-dinitrophenol (MDNP) derivatives of beta -lactoglobulins A and B ( beta -Lg A and B) were prepared in acetate buffer (pH 5.2) and 2,6-dichloromercuri-4-nitrophenol (DMNP) derivatives in Tris-HCl buffer (pH 8.2). The MDNP and DMNP reacted with both beta -Lg A and B in a stoichiometry of 2 and 1 respectively. After 24 h the derivatives were dialysed, freeze-dried and dissolved in buffers of pH 2 to 12. The circular dichroism (CD) spectra, measured at 20 deg C, of the MDNP derivatives of beta -Lg A and B were identical, with a negative band at 450 nm, a small negative shoulder at 410 nm and 2 positive bands near 350 and 315 nm. Intensities of these Cotton effects were pH-dependent. At pH 8.2 the derivatives were completely dissociated into halves. The CD spectra of the DMNP derivatives showed positive bands at 440 and 320 nm and a negative band near 355 nm. The intensities were pH-dependent, but the extrinsic Cotton effects of DMNP- beta -LgA were less pronounced than those of DMNP- beta -LgB; the latter also showed a small positive band at 385 nm. Crosslinking by the reagent prevented dissociation of either derivative in alkaline medium.n.