An Efficient and Simple Breast Milk Sample Preparation to Detect Polycyclic Aromatic Hydrocarbons by Gas Chromatography-Mass Spectrometry

Journal of Analytical Chemistry - Polycyclic aromatic hydrocarbons (PAHs) can be extremely hazardous to human health due to their carcinogenicity and toxicity. Following mother exposure, a part of...     

Effect of tetracaine on model and erythrocyte membranes by DSC and EPR

Summary DSC and EPR experiments were performed on human erythrocyte membranes and DPPC vesicles in order to study the effect of the anaesthetic drug tetracaine on structure and dynamics of the lipid region. Experiments using spin label technique showed that tetracaine induced fluidity changes of the lipid region in the environment of the fatty acid probe molecules incorporated into the membranes in the vicinity of the lipid-water interface. Similarly to EPR observations, DSC measurements reported decrease of the main melting and the pretransition temperature in comparison to control DPPC vesicles, which is the sign of destabilisation of the structure in the head group region of the lipids. Similar effect was observed in the case of erythrocytes where the protein conformation was also controlled in the presence of drug. A separated membrane melting with well distinguished membrane protein phase transition was found that was affected significantly by tetracaine. These results suggest that tetracaine is able to modify not only the internal dynamics of erythrocyte membranes and produce destabilisation of the lipid structure, but the protein system as well. These might lead to further damage of the biological functions.     

DSC study of glycerol-extracted muscle fibers in intermediate states of ATP hydrolysis

Summary The heat capacity of contractile proteins actin and myosin was studied in psoas muscle of rabbit in strongly and weakly binding state of myosin to actin as a function of temperature by DSC. Deconvolution of the unfolding scans makes possible to characterize the structural domains of the macromolecules. We tried to approach the unfolding process in different intermediate state of ATP hydrolysis. The thermal transitions were calorimetrically irreversible, therefore the two-state irreversible model that describes fairly well the denaturation of different proteins was used for evaluation of the denaturation processes in muscle fibers in strongly (rigor, ADP) and weakly binding states (ATP·V_i, ADP·AlF₄) of myosin to actin. Deconvolution resulted in four transitions, the first three transition temperatures were almost independent of the intermediate states of muscle, the last transition temperature was shifted to higher temperature, when the buffer solution was manipulated. The mean values in strongly binding states were T_m1=52.9±0.7°C, T_m2=57.9±0.7°C, T_m3=63.7±1.0°C and T_m4=67.8±0.7°C, but the last transition increased to higher temperature depending on the P_i analogue.     

DSC study on the motor protein myosin in fibre system

We have examined by DSC the complexes of myosin with actin in fibre system in the absence of nucleotides and the intermediate state of ATP hydrolysis by mimicking stable complex with myosin and ADP and beryllium fluoride in muscle fibres. Comparing the DSC results with other structural analogues of phosphate P_i leads the conclusion that the AM.ADP.BeF_x complex favours the AM.ADP.P_i complex in fibre system. The deconvolution of DSC scans resulted in four transitions, the first three transition temperatures were almost independent of the intermediate state of the muscle, the last transition temperature was shifted to higher temperature, depending on the actual intermediate states of ATP hydrolysis. In AM.ADP.V_i state the transition temperature at the second and third transitions (actin binding domain and myosin rod) varied only slightly, whereas the last one (the fourth transition) shifted markedly to higher temperature depending on the ternary complex, e.g. in case of ADP plus BeF_x it was 77.7 °C, the highest value in weakly binding state of myosin to actin. The sum of calorimetric enthalpies of the first and last curves was practically constant, but their fractions depended on the state of the muscle. In strongly binding state of myosin to actin (rigor, ADP state) the fraction of the first transition was much larger, than the last one, whereas in weakly binding state of myosin to actin, the fraction of the first transition decreased at the expense of the last one. It supports also the view that these transitions are parts of the same portion of the myosin molecule.