Novel peptides from adrenomedullary chromaffin vesicles

The adrenal medulla chromaffin vesicle (CV) contains, on a weight basis, as much soluble protein and peptide as catecholamine. The bulk of the protein is accounted for by chromogranins (Cgr) A, B and C. Additionally, a large variety of neuropeptides and their precursor proteins have been found recently within these vesicles. Nevertheless, fractionation of CV lysates indicates the presence of many more peptides than previously reported. In the hope of finding novel bioactive peptides, we initiated a systematic isolation and characterisation of CV peptides. Bovine CV pellets were prepared by sucrose gradient centrifugation and immediately boiled in water to avoid degradation of native proteins and peptides. The water lysates were fractionated through a battery of reversed-phase and ion-exchange high-performance chromatographic steps. We fully or partially characterised a substantial number of novel peptides derived from CgrA and CgrB. A tetradecapeptide and a 13 kDa extended peptide were derived from the bovine homologue of rat secretogranin III. Peptides corresponding to C-terminal fragments of 7B2 and proteoglycan 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, but others were preceded or followed by single basic residues or by unusual putative cleavage sites. Some of these peptides were postranslationally modified (pyroglutamylation, glycosylation, phosphorylation, amidation). A significant degree of structural conservation of some of these peptides across species suggests that they may exert biological effects when cosecreted with catecholamines during splanchnic stimulation.