OPOSSUM COLONIC MUCOSA CONTAINS UROGUANYLIN AND GUANYLIN PEPTIDES

Uroguanylin and guanylin are structurally related peptides that activa te an intestinal form of membrane guanylate cyclase (GC-C). Guanylin w as isolated from the intestine, but uroguanylin was isolated from urin e, thus a tissue source for uroguanylin was sought. In these experimen ts, uroguanylin and guanylin were separated and purified independently from colonic mucosa and urine of opossums. Colonic, urinary, and synt hetic forms of uroguanylin had an isoelectric point of similar to 3.0, eluted from C-18 reverse-phase high-performance liquid chromatography (RP-HPLC) columns at 8-9% acetonitrile, elicited greater guanosine 3' ,5'-cyclic monophosphate (cGMP) responses in T84 cells at pH 5.5 than pH 8, and were not cleaved and inactivated by pretreatment with chymot rypsin. In contrast, colonic, urinary, and synthetic guanylin had an i soelectric point of similar to 6.0, eluted at 15-16% acetonitrile on C -18 RP-HPLC columns, stimulated greater cGMP responses in T84 cells at pH 8 than pH 5.5, and were inactivated by chymotrypsin, which hydroly zed the Phe-Ala or Tyr-Ala bonds within guanylin. Uroguanylin joins gu anylin as an intestinal peptide that may participate in an intrinsic p athway for cGMP-mediated regulation of intestinal salt and water trans port. Moreover, uroguanylin and guanylin in urine may be derived from the intestinal mucosa, thus implicating these peptides in an endocrine mechanism linking the intestine with the kidney.