Evidence for a dipeptide transport system in renal brush border membranes from rabbit

Papain treatment of renal brush border vesicles was carried out as a successful first step towards the purification of the membrane components involved in dipeptide transport. The treated vesicles exhibited increased specific transport activity of glycyl-L-proline. In contrast, the specific transport activity of L-alanine in the treated vesicles was less than that in the control vesicles. Papain treatment resulted in the solubilization of 38% of protein, 55% of alkaline phosphatase, 90% of gamma-glutamyltransferase and 95% of leucine aminopeptidase. There was no change in the intravesicular volume nor was there any increase in vesicular permeability. Glycyl-L-proline transport was Na+-independent in the control and papain-treated vesicles. Diamide reduced the Na+-dependent L-alanine transport while glycyl-L-proline transport remained unaffected in the presence of Na+. Many dipeptides inhibited glycyl-L-proline transport both in the presence and absence of Na+. The inhibition by dipeptides was greater than the inhibition by equivalent concentrations of free amino acids. These data demonstrate that renal brush border vesicles can efficiently handle dipeptides by a mechanism completely different from that of amino acid transport.