Interactions of tetracyclines with milk allergenic protein (casein): a molecular and biological approach.

Tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC) interactions with the allergenic milk protein casein (CAS) were here evaluated simulating food conditions. The antibiotics assessed interact with CAS through static quenching and form non-fluorescent complexes. At 30 °C, the binding constant (Kb) varied from 0.05 to 1.23 × 106 M-1. Tetracycline interacts with CAS preferably through electrostatic forces, while oxytetracycline and chlortetracycline interactions occur by hydrogen bonds and van der Waals forces. The interaction process is spontaneous, and the magnitude of interaction based on Kb values, followed the order: TC < CTC < OTC. The distances between the donor (protein) and the receptors (TC, OTC, and CTC) were determined by Förster resonance energy transfer (FRET) and varied from 3.67 to 4.08 nm. Under natural feeding conditions, the citrate decreased the affinity between TC and CAS; a similar effect was observed for OTC in the presence of Ca(II), Fe(III) and lactose. Synchronized and three-dimensional (3D) fluorescence studies indicated alterations in the original protein conformation due to the interaction process, which may influence allergenic processes. In addition, complexation with CAS modulated the antimicrobial activity of CTC against S. aureus, demonstrated that the interaction process possibly alters the biological properties of antibiotics and the own protein, in the food conditions.Communicated by Ramaswamy H. Sarma.

Interactions of tetracyclines with ovalbumin, the main allergen protein from egg white: Spectroscopic and electrophoretic studies.

The interactions of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) with ovalbumin (OVA), the main allergen protein of egg white, were investigated by molecular spectroscopy and electrophoresis at three pH conditions (1.5, 4.6 and 7.4). Molecular and synchronous fluorescence, UV-vis spectroscopy, electrophoresis and 1H NMR were used to study the interaction process. Tetracyclines interact with ovalbumin fluorescence by a static quenching mechanism with non-fluorescent complex formation changing the native protein structure. The binding constant (Kb) ranged from 2.11×104 to 58.4×104Lmol-1, and corresponding thermodynamic parameters were measured at different temperatures and pH values. The binding process was spontaneous (ΔG<0), and the magnitude of the interaction increased in the following order: TC

Angiotensins processing activities in the venom and epidermic mucus of Scorpaena plumieri.

The venom of marine animals is a rich source of compounds with remarkable selectivity and functional diversity. Scorpaena plumieri is the most venomous fish in the Brazilian fauna and is responsible for relatively frequent accidents involving anglers and bathers. In humans, its venom causes edema, erythema, ecchymoses, anxiety, nausea, vomiting, and syncope. The venom is chemically characterized by Sp-CTx, a enzyme able to generate an initial endothelium-dependent relaxation response, followed by a contraction response. This study sought to investigate the proteolytic activities regarding vasopeptides angiotensin I and II. Both the venom and the epidermal mucus presented angiotensin conversion activity for angiotensin I, as well as a capacity to form Ang 1-7 directly via Ang I and II. Captopril (10 µM) and EDTA (1 mM) were able to abolish the converting activity of the venom and the epidermal mucus, representing the first description of a converting activity in S. plumieri venom and epidermal mucus.

Angiotensin processing activities in the venom of Thalassophryne nattereri.

The venom of marine animals is a rich source of compounds with remarkable functional specificity and diversity. Thalassophryne nattereri is a small venomous fish inhabiting the northern and northeastern coast of Brazil, and represents a relatively frequent cause of injuries. Its venom causes severe inflammatory response followed frequently by the necrosis of the affected area. This venom presents characterized components such as proteases (Natterins 1-4) and a lectin (Nattectin) with complex effects on the human organism. A specific inhibitor of tissue kallikrein (TKI) reduces the nociception and the edema caused by the venom in mice. Our study sought to investigate the proteolytic activities against vasopeptides Angiotensin I, Angiotensin II, Angiotensin 1-9 and Bradykinin. The venom indicated angiotensin conversion against angiotensin I, as well as kininase against bradykinin. Captopril conducted the total inhibition of the converting activity, featuring the first report of ACE activity in fish venoms.