Immunological recognition of NPS-gastrin derivatives by gastrin antibodies

Abstract

NPS-gastrin (o-nitrophenylsulfenylgastrin) derivatives are potent inhibitors of stimulated gastric acid secretion in the rat. The aim of this work is to study the recognition by a gastrin antibody of several gastrin derivatives either with or without the addition of NPS to the C-terminal tryptophan residue. We studied the following peptides and their NPS-derivatives: human gastrin I (2–17) (G), BOC-βAla-Trp-Met-Asp-PheNH 2 (pentagastrin) (Pg), its analog BOC-Gly-Trp-NLeu-Asp-PheNH 2 (NLeu-Pg) 2, t-AOC-Trp-Met-Asp-PheNH 2 9tetragastrin). In addition, (Dehydro(αβ)Trp)-pentagastrin (dehydro-Pg) was also tested. In a standard immunoassay system containing constant amounts of 125I-gastrin and gastrin antibody we measured the B F ratio with varying amounts of gastrin and the above peptides. In the case of all penta and tetrapeptide derivatives the presence of the NPS radical promoted better recognition of the molecules by gastrin antibody. On the other hand the rigidity of the side chain of the tryptophan in the dehydro-Pg analog of pentagastrin drastically decreased the affinity of gastrin antibody for the molecule ( D 50 = 1 1000 that of pentagastrin).