Gastrotropin: not an enterooxyntin but a member of a family of cytoplasmic hydrophobic ligand binding proteins.

Gastrotropin, a peptide initially isolated from porcine intestinal extracts, has been proposed to be an enterooxyntin. We have isolated a full length gastrotropin cDNA from a hog small intestinal lambda gt11 library. No evidence of co-translational translocation or processing of the encoded 127-residue protein could be demonstrated using an in vitro transcription/translation/microsomal processing assay. Comparative sequence analyses indicate that gastrotropin is a new member of the family of cytoplasmic hydrophobic ligand proteins. Analysis of the distribution of gastrotropin in nine adult Sprague-Dawley rat tissues revealed that the gene is expressed in small intestine but not in stomach, liver, heart, skeletal muscle, lung, kidney, adrenals, or brain. Bioactivity studies demonstrated that neither gastrotropin nor a carboxyl-terminally amidated tridecapeptide fragment deduced from the cDNA sequence influence acid secretory activity in rats with gastric fistulas or in isolated canine gastric parietal cells. Together these data suggest that gastrotropin is not likely to be secreted as a hormone or to function as an enterooxyntin. Moreover, it appears that gastrotropin represents one of several members of the family of hydrophobic ligand binding proteins that are expressed in the small intestine.