Synthesis of a new phosphatidylserine spin-label and calcium-induced lateral phase separation in phosphatidylserine-phosphatidylcholine membranes

Abstract

A new phosphatidylserine spin label with nitroxide stearate attached at the 2 position has been synthesized by the reaction of spin-labeled CDP-diglyceride with L-serine under the catalytic action of phosphatidylserine synthetase. Some structural properties of pure phosphatidylserine (PS) and binary PS-phosphatidylcholine (PC) membranes were studied with the spin label. PS membrane became solidified on lowering solution pH, 50% solidification being attained at pH 3.5. The membrane was also solidified by addition of Ca-2+. The effect of Ba-2+,Sr-2+, and Mg-2+ was smaller than that of Ca-2+. The calcium-induced lateral phase separation in the binary membrane was studied from the side of the calcium-receiving lipid. The results confirmed and extended our previous conclusion drawn with PC spin label. The phase diagram of the binary membrane in the presence of Ca-2+ was determined. Not all PS molecules were aggregated to form the solid patches but some remained dissolved in the fluid PC matrix. The fluid PS fraction was larger for the membranes containing more PC. The membrane with 10% PS still had a significant fraction of solid phase. The rate of calcium-induced aggregation was greatly dependent on the PS content. The aggregation was almost complete within 5 min in the membrane containing 67% PS, while it was still proceeding after several hours in the membrane with 20% PS. The rate-limiting step was suggested to be in the formation of "stable" nuclei consisting of larger aggregates. The possible biological significance of the ionotropic phase separation was discussed whereby a transient density fluctuation was emphasized.

Charge-induced phase separation in lipid membranes

“…In this respect it is worth mentioning that in Staphylococcus aureus the indispensable to include the effect of electrostatic interactions on the phase behavior in biomembranes. To emphasize even further the key role played by the charges, we note that membranes composed of a binary mixture of charged lipids was reported to undergo a phase separation induced by addition of salt, even when the two lipids have same hydrocarbon tail [16][17][18] . For this charged lipid mixture, the segregation is mediated only by the electrostatic interaction between the lipids and the electrolyte.…”

Electron Spin Resonance Studies of Erythrocytes from Patients with Duchenne Muscular Dystrophy

“…Receivedfor publication 27 May 1977 and in revisedform 7 October 1977. 'Abbreviations used in this paper: BSA, bovine serum albumin; Buffer I, 0.15 M NaCl-O.01 M Tris, pH 7.4; DMD, is associated with proximal musele weakness and atrophy, cardiac involvement, and a high rate of varying degrees of mental retardation (1). Elevated levels of muscle enzyme activities in the serum and their depletioni in the mtuscle tissue have implied an abnormality in the plasma membrane as the probable site of the genetic defect, although the primary inherited metabolic defect is unknown.…”

Therapeutic Effects of Ca2+ on Peritoneal Dissemination of Gastric Carcinoma in Vivo

“…It is well known that Ca 2+ can chelate with anionic lipids such as phosphatidylserines (PS) and induce the phase separation in the artificial cell membranes (phosphatidylcholine liposomes), though Mg 2+ less interacts with PS. [19][20][21][22] On the other hand, it was reported that the expression of PS in outer plasma membranes was more increased in the cancer cells as compared with in the normal cells. 23,24) Most recently, we have found the markedly inhibitory effects of extracellular Ca 2+ , but not Mg 2+ , on the growth of human stomach carcinoma (MKN-45) cells through the induction of apoptosis in vitro.…”