We have isolated from pig intestine a 60-residue polypeptide initially identified by its inhibition of glucose-induced insulin secretion from perfused pancreas. The amino acid sequence of this porcine polypeptide was determined and found to be markedly similar to that of the pancreatic secretory trypsin inhibitor (41% residue identities). Furthermore, the disulfide arrangements of these two proteins appear identical, suggesting related overall conformations. However, the polypeptide, now named PEC-60 (peptide with N-terminal glutamic acid, C-terminal cysteine, and a total of 60 residues), was found not to inhibit trypsin. The amino acid sequence is also similar to that of a peptide recently isolated from rat bile/pancreatic juice which stimulates the release of cholecystokinin. The biological role of PEC-60 is not known, but the effect on insulin secretion and the homologies observed suggest important biological activities and interesting structural relationships.

Two different insulin‐like growth‐factor (IGF)‐binding proteins have been found in human blood, one of high molecular mass and dependent on growth hormone for synthesis, the other of low molecular mass and independent of growth hormone. The small IGF‐binding protein is abundant in human amniotic fluid. Its amino acid sequence has now been determined by direct analysis of the protein and its proteolytic fragments. Also, by immunoscreening a partial cDNA clone was isolated from a human hepatoma cell line. The mature protein consists of 234 amino acids and is coded for by an mRNA of approximately 1700 nucleotides in length. The primary structure of the protein reveals 18 Cys residues in N‐terminal and C‐terminal clusters and an Arg‐Gly‐Asp peptide sequence, common to extracellular proteins binding to receptors of the integrin family. A protein‐sequence polymorphism was detected at position Ile/Met‐228, indicating possible allelic variation. The 3′‐untranslated mRNA sequence has a high A + T content and shows five copies of an ATTTA sequence which has been shown to be involved in the regulation of the stability of certain mRNAs coding for growth‐regulating proteins.

The NH2-terminal region of rat liver glucose-6-phosphate dehydrogenase (EC 1.1.1.49) is shown to differ radically from a reported amino acid sequence for the fruit fly enzyme and from one for the human enzyme. The results indicate considerable differences in the translational start point. However, a close relationship with another reported sequence for the human enzyme is established, now showing agreement between an indirectly deduced and a directly analyzed NH2-terminal structure of this enzyme type. The results provide evidence of one structural motif common to mammalian species but also suggest that genetic inconstancy 5' to, or at the start of, the region coding for the enzyme protein could be a source of intra-and interspecies diversity. This is of interest in relation to the large number of genetic variants of human glucose-6-phosphate dehydrogenase.