Membrane-damaging action of ricin on DPPC and DPPC-cerebrosides assemblies

Perturbations induced by a toxic lectin (ricin) on lipid organisation of model membranes prepared with DPPC and DPPC-cerebrosides mixtures have been analysed by Raman and infrared spectroscopy, two powerful and non-invasive methods. Our approach involves the observation of changes in the vibrational spectra of liquid multilayers in the PO ₂ ^- , C=0 and CH₂ spectral regions for two lipid: ricin molar ratios (225:1, 75:1).The interfacial and polar regions of the multilayers, analysed by FTIR, appear to be perturbed by the protein. With both kinds of membranes, ricin mainly perturbs the C=0 ester groups of the sn-2 acylchain of DPPC. In the PO ₂ ^- stretching region, the frequency shifts are correlated with changes in polar group hydration.In the hydrophobic core of the multilayer membrane studied by Raman spectroscopy, the interaction of ricin is associated with changes in lipid packing. These perturbations depend upon the lipid composition of the membrane. With DPPC membranes, an affect is detected at temperatures lower than T _m .It corresponds to a decrease of the lipid ordering. With DPPC-cer membranes, the protein increases the acylchain packing order regardless of the temperature of the experiments (10°C<T<75°C). No perturbation of T _m is observed after addition of ricin to either DPPC or DPPC-cer membranes.The different perturbations detected by Raman and FTIR suggest that ricin mainly interacts with the interfacial domains of the membranes.     

Effects of alginates and sodium carrageenates mixed with soy proteins on the coefficient of protein efficiency

Male 21 d-old Wistar rats, were fed for 4 wk with diets containing casein or soybean proteins (10%) with 0.5, 1, 2 or 3% sodium alginate or sodium carrageenan or without any alginate or carrageenan. Daily protein intake and weight gain of casein-fed rats were not significantly different (P less than 0.05) from those of rats fed soybean meal with alginate, whatever the dose received. Rats fed 3% carrageenan in soybean meal had significantly higher feed intake than that of rats fed casein. At the levels studied, alginate had no effect on the Protein Efficiency Ratio (PER), but carrageenan did. The addition of increased quantities of carrageenan to soybean meal followed by heating the mixture led to a progressive and significant decrease in PER at all levels of carrageenan compared to casein feeding. The addition of 3% carrageenan to heated soybean meal, corresponding to 0.62% of meal diet, led to a significant decrease in PER. These results confirm the precipitating role of carrageenans on proteins.     

Haemolysis of rabbit erythrocytes by a lectin from the seeds of<Emphasis Type="Italic">Croton tiglium</Emphasis>

The kinetics of haemolysis of rabbit erythrocytes byCroton tiglium lectin was studied as a function of concentration of the lectin and erythrocytes. The length of the prelytic period decreased with increasing lectin concentrations, indicating that the secondary events at the membrane which follow the binding of the lectin to cell surface carbohydrate receptors are accelerated at higher surface concentrations of the lectin. The rate or extent of haemolysis was not affected by the inclusion of ions like K⁺, Ca²⁺ and Mg²⁺ in the medium or by the substitution of ionic medium by a non-ionic medium. The inhibition of haemagglutination and haemolysis of rabbit red cells byCroton tiglium lectin by antilectin rabbit serum was observed. A possible mechanism of haemolysis by the lectin is discussed.     

Plant lectins specific for N-acetyl-β-D-galactosamine

N-Acetyl-D-galactosamine in β-linkage being ubiquitous in cell surface glycoproteins, their interaction with lectins specific for this sugar moiety may be a significant event in cell adhesion phenomena. This article discusses the common β-N-acetyl galactosamine-specific lectins, with particular stress on the lectin from winged beans (Psophocarpus tetragonolobus).