Mode of Interaction of Benzanthrone with Serum Proteins

Abstract

Benzanthrone, a popular anthraquinone dye-intermediate is known to cause skin and other toxicological manifestations in industrial workers exposed to it. The uptake of benzanthrone through the systemic circulation, in the form of serum protein binding, was characterised by gel filtration and fluorescence quench-ing studies. Fractionation of benzanthrone-protein complex on Sephadex G-200 column revealed that albumin was responsible for the binding with benzanthrone. Addition of benzanthrone quenched the fluorescence intensity of bovine serum al-bumin or human serum albumin with a concomitant enhancement in the fluorescence intensity of benzanthrone. The quenching of albumin fluorescence and the increase in fluorescence of benzanthrone levelled off when the molar ratio of benzanthrone to albumin reached a value of one. This was in accordance with the Scatchard plot analysis. The binding was maximum in the pH range of 7.0-8.0. Stern-Volmer plot showed a linear relationship and downward curving with human serum albumin and bovine serum albumin having an association constant of 6.17 × 10⁵M^-1 and 6.54 × 10⁵M^-1, respectively. Tryptophan was found to interact with benzanthrone and it also elicited a concentration dependent quenching of its fluorescence with a simultaneous increase in the fluorescence of benzanthrone. The likely involvement in the type II residual tryptophan in the neighbourhood of apolar hydrophobic amino acids of protein chain was anticipated. Binding potential of this dye intermediate with carrier albumin may explain the mode of transport and the ultimate toxicity in the target tissues.