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Sticholysins are α-pore-forming toxins produced by the sea-anemone Stichodactyla helianthus. These toxins exert their activity by forming pores on sphingomyelin-containing membranes. Recognition of sphingomyelin by sticholysins is required to start the process of pore formation. Sphingomyelin recognition is coupled with membrane binding and followed by membrane penetration and oligomerization. Many features of these processes are known. However, the extent of contact with each of the different kinds of lipids present in the membrane has received little attention. To delve into this question, we have used a phosphatidylcholine analogue labeled at one of its acyl chains with a doxyl moiety, a known quencher of tryptophan emission. Here we present evidence for the contact of sticholysins with phosphatidylcholine lipids in the sticholysin oligomer, and for how each sticholysin isotoxin is affected differently by the inclusion of cholesterol in the membrane. Furthermore, using phosphatidylcholine analogs that were labeled at different positions of their structure (acyl chains and headgroup) in combination with a variety of sticholysin mutants, we also investigated the depth of the tryptophan residues of sticholysins in the bilayer. Our results indicate that the position of the tryptophan residues relative to the membrane normal is deeper when cholesterol is absent from the membrane. [ABSTRACT FROM AUTHOR]

Long-chain saturated ceramides possess the ability to form gel domains in fluid bilayer membranes. Such domains may also contain sphingomyelin, but generally exclude cholesterol. We studied the effect of N-acyl chain methylations on the ability of ceramide to form ceramide- and sphingomyelin-containing gel domains that displace sterol. Fluorescence quenching of probes displaying different lateral partitioning in heterogeneous lipid bilayers showed that the methyl branches induced position-dependent changes in the lateral distribution of the ceramides. Distally monomethylated ceramides interacted with sphingomyelin and displaced sterol, whereas proximally monomethylated and polymethylated ceramides appeared to be located outside of sterol/sphingomyelin-enriched domains. The branched ceramides also markedly reduced the bilayer affinity for sterol as determined from the equilibrium partitioning of sterol between lipid vesicles and cyclodextrin. Altogether, alterations in intermolecular interactions induced by the methyl branches markedly affected the molecular properties of ceramide in artificial bilayers. [ABSTRACT FROM AUTHOR]

And by UCM-Banco Santander Grants PR75/18-21561, PR87/19-22556, and PR108/20-26896 (to A.M.-d.-P.)." now reads: "This research was supported by the Juselius Foundation (J.P.S. and J.P.-O.) And by UCM-Banco Santander Grants PR75/18-21561, PR87/19-22556, PR108/20-26896 and a REACT-EU grant from the Comunidad de Madrid to the ANTICIPA prorogued project of Complutense University of Madrid (to A.M.-d.-P.).". [Extracted from the article]

The angular distribution of the products of the C + C reaction at the energies E = 22.1, 23.5, and 24.6 MeV has been studied near a 23.5-MeV quasimolecular resonance. Channels with the yield of Be have been considered for various excitation energies of the residual nucleus. The results have been analyzed within the cluster and DWBA models. It has been shown that an approach based on the assumption of direct processes reproduces the features of the angular distributions. Oscillations corresponding to the formation of a quasimolecular resonance with an angular momentum of 12 have been detected near the resonance. [ABSTRACT FROM AUTHOR]

High-spin states of the Ne nucleus in the excitation energy range of 15-30 MeV have been studied. The angular correlation method has been used to determine the spins of excited states. A number of new states with high angular momenta-20.0 MeV (9), 20.7 MeV (11), 21.6 MeV (9), 22.2 MeV (12), and 25.0 MeV (9)-have been revealed. They are intensely populated in the reaction C(C, α)Ne* → α + O and correspond to the rotational bands of various structures. [ABSTRACT FROM AUTHOR]

Ceramides are precursors of major sphingolipids and can be important cellular effectors. The biological effects of ceramides have been suggested to stem from their biophysical effects on membrane structure affecting the lateral and transbilayer organization of other membrane components. In this study we investigated the effect of acyl chain composition in ceramides (C4-C24:1) on their miscibility with N-palmitoyl-sphingomyelin (PSM) using differential scanning calorimetry. We found that short-chain (C4 and C8) ceramides induced phase separation and lowered the Tm and enthalpy of the PSM endotherm. We conclude that short-chain ceramides were more miscible in the fluid-phase than in the gel-phase PSM bilayers. Long-chain ceramides induced apparent heterogeneity in the bilayers. The main PSM endotherm decreased in cooperativity and enthalpy with increasing ceramide concentration. New ceramide-enriched components could be seen in the thermograms at all ceramide concentrations above XCer = 0.05. These broad components had higher Tm values than pure PSM. C24:1 ceramide exhibited complex behavior in the PSM bilayers. The miscibility of C24:1 ceramide with PSM at low ( XCer = 0.05–0.10) concentrations was exceptionally good according to the cooperativity of the transition. At higher concentrations, multiple components were detected, which might have arisen from interdigitated gel-phases formed by this very asymmetric ceramide. The results of this study indicate that short-chain and long-chain ceramides have very different effects on the sphingomyelin bilayers. There also seems to be a correlation between their miscibility in binary systems and the effect of ceramides of different hydrophobic length on sphingomyelin-rich domains in multicomponent membranes. [ABSTRACT FROM AUTHOR]