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.
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.
Kramer
W
W
Hoechst Aktiengesellschaft, Frankfurt am Main, F.R.G.
Dechent
C
C
Girbig
F
F
Gutjahr
U
U
Neubauer
H
H
D000345:Affinity Labels; D000626:Aminopeptidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology; D001667:Binding, Competitive; D018826:CD13 Antigens; D002352:Carrier Proteins / Q000032:analysis / Q000378:metabolism; D002506:Cephalexin / Q000378:metabolism; D004151:Dipeptides / Q000378:metabolism*; D018819:Dipeptidyl Peptidase 4; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism*; D007163:Immunosorbent Techniques; D007408:Intestinal Absorption; D007421:Intestine, Small / Q000378:metabolism; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D008871:Microvilli / Q000201:enzymology*; D008970:Molecular Weight; D010400:Penicillin G / Q000378:metabolism; D010777:Photochemistry; D011817:Rabbits; D013552:Swine
D000345:Affinity Labels; D000900:Anti-Bacterial Agents; D002352:Carrier Proteins; D004151:Dipeptides; D010450:Endopeptidases; D000626:Aminopeptidases; D018826:CD13 Antigens; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D018819:Dipeptidyl Peptidase 4; D007930:Leucine; C012211:ubenimex; D002506:Cephalexin; D010400:Penicillin G