Binding of amino beta-lactam antibiotics to soluble protein from rat intestinal mucosa--I. Purification of drug-binding protein.

Several amino beta-lactam antibiotics, including ampicillin, amoxicillin, cyclacillin, cephalexin, cephradine and cefadroxil, were found to bind in vitro to specific components in 105,000 g supernatant of homogenate obtained from rat intestinal mucosa. The major binding component (fraction b) was purified by chromatography on DEAE-cellulofine and by gel filtration on Sephadex G-50. The molecular weight of fraction b was determined by SDS polyacrylamide gel electrophoresis (15,000 Da). The binding behaviour of these amino beta-lactam antibiotics to fraction b were estimated by equilibrium dialysis. There were significant high affinities of all tested amino beta-lactam antibiotics which were well absorbed from intestine, but there was not a good correlation between binding and absorption of these drugs. It was also found that poorly absorbed cephalosporins which lack aminobenzyl group in their structure, cefazolin and cephaloridine, did not bind to fraction b.