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  • Title: Intestinal uptake of dipeptides and beta-lactam antibiotics. I. The intestinal uptake system for dipeptides and beta-lactam antibiotics is not part of a brush border membrane peptidase.
    Author: Kramer W, Dechent C, Girbig F, Gutjahr U, Neubauer H.
    Journal: Biochim Biophys Acta; 1990 Nov 30; 1030(1):41-9. PubMed ID: 1979919.
    Abstract:
    The uptake of beta-lactam antibiotics into small intestinal enterocytes occurs by the transport system for small peptides. The role of membrane-bound peptidases in the brush border membrane of enterocytes from rabbit and pig small intestine for the uptake of small peptides and beta-lactam antibiotics was investigated using brush border membrane vesicles. The enzymatic activity of aminopeptidase N was inhibited by beta-lactam antibiotics in a non-competitive manner whereas dipeptidylpeptidase IV was not affected. The peptidase inhibitor bestatin led to a strong competitive inhibition of aminopeptidase N whereas the uptake of cephalexin into brush border membrane vesicles was only slightly inhibited at high bestatin concentrations (greater than 1 mM). Modification of brush border membrane vesicles with the histidine-modifying reagent diethyl pyrocarbonate led to a strong irreversible inhibition of cephalexin uptake whereas the activity of aminopeptidase N remained unchanged. A modification of serine residues with diisopropyl fluorophosphate completely inactivated dipeptidylpeptidase IV whereas the transport activity for cephalexin and the enzymatic activity of aminopeptidase N were not influenced. With polyclonal antibodies raised against aminopeptidase N from pig renal microsomes the aminopeptidase N from solubilized brush border membranes from pig small intestine could be completely precipitated; the binding protein for beta-lactam antibiotics and oligopeptides of apparent Mr 127,000 identified by direct photoaffinity labeling with [3H]benzylpenicillin showed no crossreactivity with the aminopeptidase N anti serum and was not precipitated by the anti serum. These results clearly demonstrate that peptidases of the brush border membrane like aminopeptidase N and dipeptidylpeptidase IV are not directly involved in the intestinal uptake process for small peptides and beta-lactam antibiotics and are not a constituent of this transport system. This suggests that a membrane protein of Mr 127,000 is (a part of) the uptake system for beta-lactam antibiotics and small peptides in the brush border membrane of small intestinal enterocytes.
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