Prouroguanylin and proguanylin: purification from colon, structure, and modulation of bioactivity by proteases.

Uroguanylin and guanylin are peptides isolated from urine and intestinal mucosa, which regulate cyclic GMP production in enterocytes by activating an apical membrane, receptor-guanylate cyclase. This study extended our previous findings, which showed that colonic mucosa of opossums contained uroguanylin and guanylin peptides, by purifying prouroguanylin and proguanylin from this tissue. Prouroguanylin and proguanylin coeluted from Sephadex G-75 gelfiltration columns with a similar molecular size between 6 and 12 kDa. Mass spectrometry indicated that proguanylin (approximately 8.7 kDa) had a 10% lower molecular mass than prouroguanylin (approximately 9.7 kDa). Isoelectric focusing separated prouroguanylin (pI approximately 4.5) from proguanylin (pI approximately 7.5). N-terminal sequence analysis of reverse phrase-HPLC purified prohormones revealed 13 amino acids in opossum proguanylin that shared 77-85% identity with human and rat proguanylin, but only 23% identity with opossum prouroguanylin. The N-termi...