Pro-vasopressin and pro-oxytocin are prohormones processed in the neurointermediate lobe pituitary to form the biologically active peptide hormones, arginine vasopressin (AVP) and oxytocin. Neurointermediate lobe pituitaries from normal (+/+), heterozygous (+/−), PC2-Null (−/−), PC1/3-Null and oxytocin-Null mice were analyzed by SELDI-TOF mass spectroscopy for the peptide hormone products, AVP, oxytocin and neurophysin I and II. Molecular ion species with masses characteristic of oxytocin, AVP, neurophysin I and II, i.e. 1009·41, 1084·5, 9677 and 9679 daltons respectively, were identified in all but the oxytocin-Null mice by comparison with synthetic standards or by C-terminal sequence analysis. Other ion species were found specifically in PC2-Null, heterozygote or normal mice. The results indicate that, in mice, both PC1/3 or PC2 enzyme activity are capable, but not required to correctly process pro-vasopressin or pro-oxytocin to their constituent active peptide hormones.

Selling SELDI Peptide identification and analysis are important elements of proteomics research. Precursor peptide hormones often differ at the carboxyl terminus to allow for altered enzymatic regulation and cleavage to the active hormone moiety. Methods describing the use of carboxypeptidase Y (CPY) to digest prohormone and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry to analyze the resultant peptide sequences have been described, but peptide identification is often difficult in complex samples containing adjacent peptide ion peaks. Cool and Hardiman (p. 32) extend carboxyl-terminal sequencing analysis to surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectrometry, which allows for its application to complex mixtures of peptides and proteins (tissue homogenates). The authors provide an additional tool for the investigation of prohormone processing in order to understand the regulation of endocrine protein hormone pathways.