Abstract
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 γ-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.
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