PEPTIDE .5. A VGF-DERIVED NEUROPEPTIDE PURIFIED FROM BOVINE POSTERIORPITUITARY

The objective of this study was to purify PRL-releasing factor (PRF) f rom the bovine posterior pituitary (PP) and determine its structure. F ive hundred bovine PP) were acid extracted and fractionated using gel filtration chromatography followed by semipreparative and analytical H PLC. PRF activity was determined by an in vitro bioassay. After six ch romatographic steps, a single peak with PRF activity was resolved. As determined by mass spectrometry and microsequencing, this peak contain ed a major peptide composed of 30 amino acids with a mol wt of 3708K. A synthetic peptide was then produced by solid-phase synthesis. When t ested both in vivo and in vitro, the synthetic peptide lacked PRF acti vity. Further HPLC fractionation under different conditions resolved t he synthetic peptide from a highly purified PRF activity. This indicat ed that the isolated peptide was coincidentally eluted with PRF during the purification. The major isolated peptide has 94% identity with a sequence at the C-terminus of a rat protein named VGF. VGF is a nerve growth factor-inducible protein that has been identified in PC12 cells and is localized in selected sites throughout the central nervous sys tem. The isolated peptide has an Arg-Arg cleavage site at its junction within the VGF protein. Based on this information, we named this subs tance Peptide V (VGF-derived peptide). We postulate that Peptide V is: 1) a natural cleavage product of the VGF protein; 2) produced and pro cessed either in the hypothalamus or within the pituitary proper, and 3) a releasable peptide that fulfills one or more endocrine functions.