Interaction of calcium ions with gastrin fragments of increasing chain length

✍ Scribed by E. Peggion; M. T. Foffani; E. Wünsch; L. Moroder; M. Goodman; S. Mammi

• Publisher: Wiley (John Wiley & Sons)
• Year: 1986
• Tongue: English
• Weight: 815 KB
• Volume: 25
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360250110

✦ Synopsis

The interaction of a series of biologically active gastrin fragments with calcium ions has been investigated by CD in trifluoroethanol. It was found that the gastrin octapeptide pGl~l~,Nle'~-HG[lO-171 binds one calcium ion per molecule. The hypothesis is made that the binding involves the Gterminal, biologically important tetrapeptide. When the chain is elongated to the gastrin nonamer pGl~g,Nle~~-HG[9-171, a second binding site is available, which is most likely situated at the N-terminal part of the molecule. Further elongation of the peptide chain up to the dodecapeptide pGl~~,Nle'~-HG [6][7][8][9][10][11][12][13][14][15][16][17] does not provide any additional binding site. Saturation of the two sites in the shorter peptides produces different changes in the chiroptical properties in the near-and far-uv. As the chain is elongated, this difference tends to disappear. This result is consistent with an increased conformational order of the longer peptides. In the shorter fragments, the strength of this second binding is appreciably lower than that of the first, while in the longer peptides, the strength of the two bindings is comparable. On the assumption that the variation of the CD properties is proportional to the extent of binding, the constant for the binding of the second ion was determined to be of the order of 5x 105 L/rnol for the nonapeptide.