Monomolecular layers of lipids at the aidwater interface have been used a s a model membrane to study membrane interactions of the lantibiotic nisin. The natural lantibiotics nisin A and nisin Z proved to have a high affinity for the anionic lipids phosphatidylglycerol and bis(phosphatidy1)glycerol (cardiolipin). The interaction with zwitterionic phopholipids or neutral lipids is very low at surface pressures higher than 32 mN/m. Nisin, nisin mutants and lacticin 481 show a remarkable correlation between antimicrobial activity and anionic lipid interaction. The results indicate that primarily the N-terminal part (residues 1-22) penetrates into the lipid phase. Reduction of the flexibility at positions 20-21 has a negative effect on monolayer interaction and activity. The C-terminal part is probably responsible for ionic interactions of nisin in monomeric or oligomeric form with anionic lipids. In mixtures of anionic and zwittcrionic lipids maximal interactions are found at approximately 70 mol/l 00 mol anionic lipid. Gram-positive bacteria, which form the main target for nisin, are characterized by a high content of anionic lipids in the membrane. Monolayers formed of lipid extracts of bacteria sensitive to nisin were more strongly penetrated than those of bacteria relatively insensitive to nisin.

No abstract

No abstract

The phosphatidylcholine exchange protein from bovine liver catalyzes the transfer of phosphatidylcholine between rat liver mitochondria and sonicated liposomes. The effect of changes in the liposomal lipid composition and ionic composition of the medium on the transfer have been determined. In addition, it has been determined how these changes affected the electrophoretic mobility i.e. the surface charge of the membrane particles involved. Transfer was inhibited by the incorporation of negatively charged phosphatidic acid, phosphatidylserine, phosphatidylglycerol and phosphatidylinositol into the phosphatidylcholine-containing vesicles ; zwitterionic phosphatidylethanolamine had much less of an inhibitory effect while positively charged stearylamine stimulated. The cation Mg2+ and, to a lesser extent, K + overcame the inhibitory effect exerted by phosphatidic acid, in that concentration range where these ions neutralized the negative surface charge most effectively. Under conditions where Mg2+ and K + affected the membrane surface charge relatively little inhibition was observed. In measuring the protein-mediated transfer between a monolayer and vesicles consisting of only phosphatidylcholine, cations inhibited the transfer in the order La3+ > M$+ 2 Ca2+ > K + = Na+. Inhibition was not related to the ionic strength, and very likely reflects an interference of these cations with an electrostatic interaction between the exchange protein and the polar head group of phosphatidylcholine.The phosphatidylcholine exchange protein from bovine liver functions as a carrier of phosphatidylcholine between membrane interfaces [l]. Recently it was demonstrated that the protein-mediated transfer of phosphatidylcholine between phosphatidylcholine liposomes was inhibited by incorporation of phosphatidic acid or phosphatidylinositol into these liposomes [2]. Steady state analysis of the kinetic data indicated that the apparent dissociation constant of the exchange protein-liposome complex decreased with an increasing phosphatidic acid content of the liposomes [3]. This was interpreted to mean that an increase of the negative surface charge facilitated the interaction of the exchange protein with the membrane interface resulting in less protein free in the medium to function as a carrier i.e. inhibition of transfer.The former studies implied that physical chemical properties of the interface may have an effect on the activity of the exchange protein. In the present study this concept has been elaborated by correlating the protein-mediated transfer of phosphatidylcholine between rat liver mitochondria and liposomes with the surface charge of these membrane structures. Comparable studies on the relationship between surface charge and phospholipase action have indicated that the surface charge of a phospholipid interface may control the formation of the proper enzyme-phospholipid complex [4].The surface charge of a membrane is the resultant of two counteracting factors, namely, the surface charge density of the membrane and the counte...

Morphological, biochemical, and physicochemical studies of myelin subfractions were undertaken on the progeny of Sprague-Dawley rats fed diets containing lipids either extracted from yeasts grown on n-alkanes or from margarine. Myelin subfractions obtained from pooled brain homogenates of littermates by sucrose density gradient centrifugation at 7, 14, and 21 days postnatally were subjected to electron microscopy, sodium dodecylsulfate polyacrylamide gel electrophoresis and assayed for 2', 3' cyclic nucleotide 3'-phosphohydrolase activity (CNPase; EC 3.1.4.37). Additionally, surface pressure measurements were made of lipid monolayers derived from myelin subfractions, which were subsequently injected with myelin basic proteins. The myelin subfractions of test animals, when compared with those of controls, show an earlier increase in the specific activity of CNPase, the earlier appearance of low-molecular-weight proteins, and an increase in the affinity of basic proteins for lipids derived from the myelin light fraction. This biochemistry suggests the presence of a more mature myelin between 7 and 14 days in the experimental group. The morphological studies, however, do not seem to concur with the biochemical data. The observed changes are discussed in relation to the influence of dietary lipids on myelinogenesis.