Proposed schemes for the metabolic cleavage of exendin-4 in rat (a) kidney and (b) liver homogenates.

<p>Arrowheads indicate cleavage sites in exendin-4: solid arrowheads, sites of concomitantly detected N- and C-terminal counterparts; open arrowheads, only N-terminal fragment detected; up arrowheads, only C-terminal fragment detected. Grey symbols indicate cleavage sites that are targeted at the onset of incubation. Black symbols indicate cleavage sites that are targeted in major metabolites or intact exendin-4 by sequential cleavage via aminopeptidase or carboxypeptidase activity.</p>