No abstract

No abstract

No abstract

Abstract— Photobinding of sulfanilamide to bovine serum albumin (BSA) was investigated by irradiating BSA and buffered BSA/drug solutions with UV light (Λ= 300 nm) under anaerobic conditions. The protein solutions were then denatured and the unbound sulfanilamide removed. Marked differences in the UV and fluorescence spectra of the solutions before and after irradiation were observed, suggesting covalent binding of the drug to BSA. This was confirmed using [14C]labelled sulfanilamide. The extent of photobinding of sulfanilamide determined using the radiolabeled drug, was concentration dependent. The binding ratio varied from 3 mol drug per mol BSA for a 10‐4M drug concentration, to 10 mol drug per mol BSA for 10‐2M drug concentration. The protein solutions were hydrolysed under acid conditions and the amino acids obtained were analysed by ion exchange chromatography. The hydrolysate of irradiated BSA (10‐4M) ‐sulfanilamide (10‐2M) mixture lost about 10 mol of cystine per mol of BSA. This loss was not observed after hydrolysis of irradiated alone or non‐irradiated BSA. Irradiation of cystine with [14C]sulfanilamide in HC1 solutions produced the same compound as was found after hydrolysis of irradiated BSA/sulfanilamide mixtures. This was demonstrated by autoradiography of paper chromatograms. The same compound was also detected in an irradiated [35S]cystine non‐labelled sulfanilamide mixture. It was not detected, however, after irradiation of a mixture of all amino acids of BSA excluding cystine. These data suggest that cystine residues are involved in the photobinding of sulfanilamide (or its photoproducts) to BSA.