Propolis is a bee product that results from the mixture of beeswax and resinous compounds. It can scavenge free radicals; therefore, it displays antioxidant activity. Here, we have investigated the antioxidant potential of propolis produced by three Brazilian stingless bee species: Melipona quadrifasciata anthidiodes (Mandaçaia) and Tetragona clavipes (Borá), which inhabit the southeastern region of Brazil (state of São Paulo), and Scaptotrigona spp. (Tubi), which inhabits the northeastern region of Brazil (state of Maranhão). The antioxidant activities of propolis produced by different bee species were compared to the well-known antioxidant activity of green propolis, produced by the honey bee Apis mellifera. The ethanolic extract of propolis produced by Mandaçaia displayed the strongest antioxidant activity. The activity was even stronger than the antioxidant activity of green propolis. The ethyl acetate and aqueous fraction of propolis produced by Mandaçaia presented the highest antioxidant activity. This result agreed with the higher total polyphenol content verified in this propolis. high performance liquid chromatography analysis revealed that the groups of compounds present in propolis produced by Mandaçaia, Tubi, and Borá were not the same as those previously identified as the main constituents of green propolis. In fact, propolis produced by Mandaçaia contained many other polyphenols in the fingerprint, and hence its composition requires further elucidation.

Crotoxin (CTX) is the main neurotoxin found in Crotalus durissus rattlesnake venoms being composed by a nontoxic and non-enzymatic component (CA) and a toxic phospholipase A₂ (CB). Previous crystallographic structures of CTX and CB provided relevant insights: (i) CTX structure showed a 1:1 molecular ratio between CA and CB, presenting three tryptophan residues in the CA/CB interface and one exposed to solvent; (ii) CB structure displayed a tetrameric conformation. This study aims to provide further information on the CTX mechanism of action by several biophysical methods. Our data show that isolated CB can in fact form tetramers in solution; however, these tetramers can be dissociated by CA titration. Furthermore, CTX exhibits a strong reduction in fluorescence intensity and lifetime compared with isolated CA and CB, suggesting that all tryptophan residues in CTX may be hidden by the CA/CB interface. By companying spectroscopy fluorescence and SAXS data, we obtained a new structural model for the CTX heterodimer in which all tryptophans are located in the interface, and the N-terminal region of CB is largely exposed to the solvent. Based on this model, we propose a toxic mechanism of action for CTX, involving the interaction of N-terminal region of CB with the target before CA dissociation.