Binding of amino beta-lactam antibiotics to soluble protein from rat intestinal mucosa--II. Mutual inhibition of binding among amino beta-lactam antibiotics and binding characteristics.

The characteristics of binding of amino beta-lactam antibiotics including ampicillin, amoxicillin, cephalexin and cephradine to fraction b obtained from the 105,000 g supernatant of rat small intestinal mucosa was investigated. The mutual inhibition of binding among these antibiotics was observed, and these were dependent on the concentration of inhibitors. It was found that dipeptides such as L-carnosine and glycylglycine significantly reduced the binding of cephalexin to fraction b, but the binding of cephradine was only slightly decreased by these dipeptides. Furthermore, the binding of cephalexin and cephradine was not influenced by amino acids (L-phenylalanine, glycine). Although ANS(1-anilino-8-naphthalenesulfonic acid magnesium salt), which is a hydrophobic probe, bound to the fraction b, there was no competitive inhibition in binding between ANS and amino beta-lactam antibiotics. The Scatchard plot of binding data of cephalexin gave two dissociation constant (Kd) values (1.37 and 15.7 microM). On the other hand, one Kd value (11.2 microM) was obtained for ampicillin.