PATTERN CHANGES OF PITUITARY PEPTIDES IN RAT AFTER SALT-LOADING AS DETECTED BY MEANS OF DIRECT, SEMIQUANTITATIVE MASS-SPECTROMETRIC PROFILING

We have established a differential peptide display method, based on a mass spectrometric technique, to detect peptides that show semiquantit ative changes in the neurointermediate lobe (NIL) of individual rats s ubjected to salt-loading, We employed matrix-assisted laser desorption /ionization mass spectrometry, using a Single-reference peptide in com bination with careful scanning of the whale crystal rim of the matrix- analyte preparation, to detect in a semiquantitative manner the molecu lar ions present in the unfractionated NIL homogenate. Comparison of t he mass spectra generated from Nn homogenates of salt-loaded and contr ol rats revealed a selective and significant decrease in the intensiti es of several molecular ion species of the NIL homogenates from salt-l oaded rats, These ion species, which have masses that correspond to th e masses of oxytocin, vasopressin, neurophysins, and an unidentified p utative peptide, were subsequently chemically characterized, We confir med that the decreased molecular ion species are peptides derived excl usively from propressophysin and prooxyphysin (i.e., oxytocin, vasopre ssin, and various neurophysins). The putative peptide is carboxyl-term inal glycopeptide. The carbohydrate moiety of the latter peptide was d etermined by electrospray tandem MS as bisected biantennary Hex(3)HexN Ac(5)Fuc. This posttranslational modification accounts for the mass di fference between the predicted mass of the peptide based on cDNA studi es and the measured mass of the mature peptide.