Interactions of photosensitized tetracycline with serum albumin.

Interactions of tetracycline with bovine serum albumin (BSA) were studied by fluorescence quenching and circular dichroism (CD) analysis. The binding isotherm exhibited at least 13 tetracycline binding sites on the albumin molecule. Amongst these, four were found to be high affinity sites and the remainder were loose sites. The Scatchard analysis demonstrated the binding constant and capacity of BSA to be 4.6 x 10(6) liters/mole and 3.6, respectively. The CD data revealed a significant decrease in the mean residue ellipticity (MRE), indicating alterations in the protein helicity. A reduction of 20% in the alpha-helical content of the albumin was noted at higher levels of tetracycline in the presence of Cu (II) ions. Thus the strong in vitro interactions of tetracycline with albumin resulted in conformational changes in its globular structure and insinuate potential health risk due to possible macromolecular damage, under physiological conditions, from the formation of tetracycline/Cu(II) complexes.