Of the many examples of post-translational processing of precursor proteins, proteolysis remains an important element in generating structural and functional diversity. Most growth factors are synthesized as soluble precursor proteins. These precursors lack specific biological activities and are primarily confined to Golgi or lysosomal compartments within the cell. Proteolytic cleavage of these precursors generates the mature growth factors which are then secreted from the cell. Specialized eukaryotic proteinases appear to be responsible for the proteolytic processing of prohormones, neuropeptide precursors, and other growth factor precursors. These proteinases are remarkably specific and cleave at particular sequences of basic residues. Subsequent to cleavage by these proteinases, a particular pathway further processes the polypeptides to generate biologically active, alpha-carboxamidated peptides. Assays have been developed for the alpha-carboxamidated peptides and their immediate precursors, the glycine-extended forms. The alpha-carboxamidated peptides have been derivatized as the alpha-carboxyl-dansylated peptides. These fluorescent peptides have been purified using newly developed chromatographic procedures. The danylated peptides are particularly challenging to purify due to their hydrophobic nature. Tissue extracts from heart, pituitary, and salivary gland are being screened for polypeptides arising from proteolysis. Several """"""""peptides"""""""" have been identified using these assays. These """"""""peptides"""""""" are currently undergoing structural analysis by mass spectrometry, amino acid analysis, and sequential Edman degradation.
