NOVEL PEPTIDES FROM ADRENOMEDULLARY CHROMAFFIN VESICLES

The adrenal medulla chromaffin vesicle (CV) contains, on a weight basi s, as much soluble protein and peptide as catecholamine. The bulk of t he protein is accounted for by chromogranins (Cgr) A, B and C. Additio nally, a large variety of neuropeptides and their precursor proteins h ave been found recently within these vesicles. Nevertheless, fractiona tion of CV lysates indicates the presence of many more peptides than p reviously reported. In the hope of finding novel bioactive peptides, w e initiated a systematic isolation and characterisation of CV peptides . Bovine CV pellets were prepared by sucrose gradient centrifugation a nd immediately boiled in water to avoid degradation of native proteins and peptides. The water lysates were fractionated through a battery o f reversed-phase and ion-exchange high-performance chromatographic ste ps. We fully or partially characterised a substantial number of novel peptides derived from CgrA and CgrB. A tetradecapeptide and a 13 kDa e xtended peptide were derived from the bovine homologue of rat secretog ranin III. Peptides corresponding to C-terminal fragments of 7B2 and p roteoglycan II were also found. Additionally, several sequences had no known precursors. Of the sequences derived from known precursors some corresponded to fragments bracketed by pairs of basic amino acids, bu t others were preceded or followed by single basic residues or by unus ual putative cleavage sites. Some of these peptides were postranslatio nally modified (pyroglutamylation, glycosylation, phosphorylation, ami dation). A significant degree of structural conservation of some of th ese peptides across species suggests that they may exert biological ef fects when cosecreted with catecholamines during splanchnic stimulatio n.