Pattern changes of pituitary peptides in rat after salt-loading as detected by means of direct, semiquantitative mass spectrometric profiling

Pattern changes of pituitary peptides in rat after salt-loading as detected by means of direct, semiquantitative mass spectrometric profiling

^*Graduate School Neurosciences Amsterdam, Research Institute Neurosciences Vrije Universiteit, Faculty of Biology, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands; ^†Boston University School of Medicine, Mass Spectrometry Resource, Department of Biophysics, 715 Albany Street, Boston, MA 02118-2394; ^‡Universität Frankfurt, Instrumentelle Analytik/Chemie für Mediziner, Theodor-Stern-Kai 7, 60596 Frankfurt, Germany; ^§Westfälische Wilhelms-Universität, Institut für Medizinische Physik and Biophysik, Robert-Koch-Strasse 31, 48149 Münster, Germany; and ^¶Universiteit Utrecht, Rudolf Magnus Instituut, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands

Edited by Susan E. Leeman, Boston University School of Medicine, Boston, MA, and approved June 3, 1997 (received for review September 18, 1996)

Abstract

We have established a differential peptide display method, based on a mass spectrometric technique, to detect peptides that show semiquantitative changes in the neurointermediate lobe (NIL) of individual rats subjected to salt-loading. We employed matrix-assisted laser desorption/ionization mass spectrometry, using a single-reference peptide in combination with careful scanning of the whole crystal rim of the matrix-analyte preparation, to detect in a semiquantitative manner the molecular ions present in the unfractionated NIL homogenate. Comparison of the mass spectra generated from NIL homogenates of salt-loaded and control rats revealed a selective and significant decrease in the intensities of several molecular ion species of the NIL homogenates from salt-loaded rats. These ion species, which have masses that correspond to the masses of oxytocin, vasopressin, neurophysins, and an unidentified putative peptide, were subsequently chemically characterized. We confirmed that the decreased molecular ion species are peptides derived exclusively from propressophysin and prooxyphysin (i.e., oxytocin, vasopressin, and various neurophysins). The putative peptide is carboxyl-terminal glycopeptide. The carbohydrate moiety of the latter peptide was determined by electrospray tandem MS as bisected biantennary Hex₃HexNAc₅Fuc. This posttranslational modification accounts for the mass difference between the predicted mass of the peptide based on cDNA studies and the measured mass of the mature peptide.

Footnotes

This paper was submitted directly (Track II) to the Proceedings Office.
Abbreviations: DHB, 2,5-dihydroxy-benzoic acid; ESI, electrospray ionization; CID, collision-induced dissociation; CPP, C-terminal glycopeptide of propressophysin; MALDI, matrix-assisted laser desorption/ionization; NIL, neurointermediate lobe.