The hemoglobin ␣-chain fragment PVNFKFLSH, which we have named hemopressin, produced dose-dependent hypotension in anesthetized rats, starting at 0.001 g/kg. The hypotensive effect of the peptide was potentiated by enalapril only at the lowest peptide dose. These results suggest a role for hemopressin as a vasoactive substance in vivo. The identification of these putative intracellular substrates for ep24.15 and ep24.16 is an important step toward the elucidation of the role of these enzymes within cells. Endopeptidase EC 3.4.24.15 (ep24.15; also referred to as thimet oligopeptidase) and endopeptidase EC 3. 4.24.16 (ep24.16; also referred to as neurolysin) were initially detected in and purified from rat brain homogenates (1, 2). The cloned rat brain ep24.16 (3) showed 80% similarity and 63% identity with the previously cloned rat testis ep24.15 (4). Both peptidases share most of their natural substrates, including bradykinin, neurotensin, opioids, angiotensin I, and gonadotrophinreleasing hormone (5, 6

From January, 1984 to December, 1996, 422 patients (ages 9 m-99 y, median 29 y) were admitted after being bitten by spiders which were brought and identified as Phoneutria spp. Most of the bites occurred at March and April months (29.2%), in the houses (54.5%), during the day (76.5%), and in the limbs (feet 40.9%, hands 34.3%). Upon hospital admission, most patients presented only local complaints, mainly pain (92.1%) and edema (33.1%) and were classified as presenting mild (89.8%), moderate (8.5%) and severe (0.5%) envenomation. Few patients (1.2%) did not present signs of envenomation. Severe accidents were only confirmed in two children (9 m, 3 y). Both developed acute pulmonary edema, and the older died 9 h after the accident. Patients more than 70 year-old had a significantly greater (p<0.05) frequency of moderate envenomations compared to the 10-70-year-old individuals. Proceedings to relief local pain were frequently performed (local anesthesia alone 32.0%, local anesthesia plus analgesics 20.6% and oral analgesics alone 25. 1%). Only 2.3% of the patients (two cases classified as severe and eight as moderate, eight of them in children) were treated with i.v. antiarachnid antivenom. No antivenom early reaction was observed. In conclusion, accidents involving the genus Phoneutria are common in the region of Campinas, with the highest risk groups being children under 10 years of age and adults over 70 years of age. Cases of serious envenomation are rare (0.5%).

Crotoxin, the main toxin of South American rattlesnake (Crotalus durissus terrificus) venom, was the first snake venom protein to be purified and crystallized. Crotoxin is a heterodimeric beta-neurotoxin that consists of a weakly toxic basic phospholipase A(2) and a non-enzymatic, non-toxic acidic component (crotapotin). The classic biological activities normally attributed to crotoxin include neurotoxicity, myotoxicity, nephrotoxicity and cardiotoxicity. However, numerous studies in recent years have shown that crotoxin also has immunomodulatory, anti-inflammatory, anti-microbial, anti-tumor and analgesic actions. In this review, we describe the historical background to the discovery of crotoxin and its main toxic activities and then discuss recent structure-function studies and investigations that have led to the identification of novel pharmacological activities for the toxin.

Extralysosomal proteolysis by multicatalytic complexes such as the 26S proteasome produces large amounts of peptides in the cytosol, mitochondria and nuclei of eukaryotic cells, and there is increasing evidence that the resulting free intracellular peptides can modulate specific protein interactions. The demonstration that free peptides added to the intracellular milieu can regulate cellular functions mediated by protein interactions suggests new putative roles for these molecules in gene regulation, metabolism, cell signaling and protein targeting. Such interactions frequently involve specific consensus amino acid sequences that can be predicted based on similarities in domain composition. We have recently developed a new strategy for identifying novel natural peptides, the sequences of which correspond to fragments of intracellular proteins and contain putative post-translational modification sites. In this review, we examine the evidence that intracellular peptides released by proteasomes may be involved in regulating protein interactions. In particular, the role of endopeptidase 24.15 (thimet oligopeptidase; EC 3.4.24.15) is discussed in detail as this enzyme has been implicated in intracellular peptide metabolism in vivo in concert with the 26S proteasome. Keywords: antigen presentation, oligopeptidase, phosphorylation, proteasome, signaling, targeting. Peptides and intracellular signalingIn addition to their well-known receptor-mediated and antigenic functions, some peptides are also involved in intracellular processes. This relatively new intracellular function for peptides is important for protein-protein, protein-RNA and protein-DNA interactions involved in cell homeostasis, and is frequently mediated by short, unstructured sequences that specifically interact with peptidebinding domains (Pawson and Scott 1997;Gavin et al. 2002). Signaling domains can be identified through their consensus amino acid sequences (Blobel and Sabatini 1970;Palade 1975) and allow the binding properties and biological functions of a protein to be predicted on the basis of domain composition (Pawson and Nash 2003).Regulatory regions in proteins are frequently produced in a cassette-like fashion from domains that mediate molecular interactions or have enzymatic activity. Several interaction domains are present in hundreds of copies in the human proteome, and these are used repeatedly to regulate distinct aspects of cellular organization. For example, about 115 Src homology 2 (SH2) and 253 Src homology 3 (SH3) domains are encoded by the human genome (Pawson and Nash 2003