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We have demonstrated that wheatwin1, a wheat pathogenesis-related protein of class 4 (PR4), has ribonuclease activity. Both native and recombinant proteins hydrolyse RNA from wheat coleoptils and have antifungal activity. Sepharosebound wheatwin1 is able to interact with either wheat or Fusarium culmorum RNA. 3D modelling studies showed that, like ribonucleases A and T1, the action mechanism should involve two His residues, an Arg residue and an Asp residue.

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The white-rot fungus Trametes trogii excretes a main laccase showing a molecular mass of 70 kDa, acidic isoelectric point and N-terminal sequence homologous to that of several phenol oxidases. The purified enzyme oxidizes a number of phenolic and non-phenolic compounds; recalcitrant molecules may be converted into substrates by introducing, in the correct position, o- or p-orienting ring-activating groups.

We conclude that catestatin is cleaved extensively in vivo, and the peptide is released by exocytosis. In chromaffin granules, the major form of catestatin is cleaved at dibasic sites, while smaller carboxyl-terminal forms also occur. Knowledge of cleavage sites of catestatin from chromogranin A may provide a useful starting point in analysis of the relationship between structure and function for this peptide.Chromogranin A, the major soluble protein in catecholamine storage vesicles, not only stabilizes the core of such vesicles (1) but also serves as a prohormone cleaved into several biologically active peptides, including the insulin release-inhibitory fragments pancreastatin (2) and ␤-granin (3-5), the vasodilator vasostatin (6, 7), and the parathyroid hormone release-inhibitory parastatin (8). Recently we described an additional chromogranin A fragment, catestatin (bovine chromogranin A 344 -364), which acts specifically as a potent (IC 50 ϳ200 -400 nM) nicotinic cholinergic antagonist to inhibit catecholamine release (9, 10), suggesting a novel autocrine feedback mechanism controlling sympathochromaffin exocytosis. Initial studies of catestatin relied on synthetic peptides (10); hence, the existence of the peptide in vivo remains unexplored, as do its precise cleavage sites from chromogranin A.In this study, we explored processing of the catestatin region of chromogranin A in secretory granules of chromaffin cells and sympathetic nerves, as well as in human pheochromocytomas. We documented catestatin cleavage from chromogranin A and determined the precise endogenous cleavage sites bounding catestatin in bovine and human chromaffin granules by chromatographic separations coupled with amino-terminal amino acid sequencing, immunoprecipitation, and matrix-assisted laser desorption ionization (MALDI) 1 mass spectrometry. We confirmed catestatin's regulated secretion by chromaffin cells. A major form of catestatin was processed at dibasic sites (bovine chromogranin A 332-364 or human chromogranin A 340 -372 ), while a smaller form was also identified (bovine chromogranin A 343-362 ). Both larger and smaller size forms were synthesized; each displayed specific antagonism of nicotinic cholinergicstimulated catecholamine release, while the smaller form had greater potency of inhibition. MATERIALS AND METHODS Preparation of TissueFractions-All preparative steps on tissues or protein fractions were conducted at 0 -4°C. Bovine adrenal medullary chromaffin granules were prepared by centrifugation on 0.3 M/1.6 M sucrose density step gradients, as described previously (10). After granule hypotonic lysis and centrifugal removal of granule membranes, the soluble proteins and peptides in the supernatant were size-fractionated on a 2.6 ϫ 80-cm Sephacryl S-300 column (Amersham Pharmacia Biotech), eluting with the volatile buffer 0.3 M ammonium acetate, pH 6.5, as described previously (11). The buffer was removed by lyophilization before further studies. In some experiments, bovine chromaffin granule proteins/peptides (200 l c...