Influence of the curvature on the water structure in the headgroup region of phospholipid bilayer studied by the solvent relaxation technique.

Solvent relaxation (SR) in 1,2-dioleoyl-palmitoyl-sn-glycero-3-phosphocholine (DOPC) unilamellar vesicles of different size was probed by 6-hexadecanoyl-2-(((2-(trimethylammonium)ethyl)methyl)amino)naphthalene chloride (Patman), 6-propionyl-2-dimethylaminonaphthalene (Prodan) and 4-[(n-dodecylthio)methyl]-7-(N,N-dimethylamino)-coumarin (DTMAC). Patman probes the amount and mobility of the bound water molecules located at the carbonyl region of the bilayer. Membrane curvature significantly accelerates the solvent relaxation process, but does not influence the total Stokes shift, showing that membrane curvature increases the mobility, without affecting the amount of water molecules present in the headgroup region.

Interactions of histatin 5 and histatin 5-derived peptides with liposome membranes: surface effects, translocation and permeabilization.

A number of cationic antimicrobial peptides, among which are histatin 5 and the derived peptides dhvar4 and dhvar5, enter their target cells and interact with internal organelles. There still are questions about the mechanisms by which antimicrobial peptides translocate across the membrane. We used a liposome model to study membrane binding, translocation and membrane-perturbing capacities of histatin 5, dhvar4 and dhvar5.

pH-dependent Ca2+ binding to the F0 c-subunit affects proton translocation of the ATP synthase from Synechocystis 6803.

It was shown before (Wooten, D. C., and Dilley, R.

Introduction of a carboxyl group in the loop of the F0 c-subunit affects the H+/ATP coupling ratio of the ATP synthase from Synechocystis 6803.

The proton translocation stoichiometry (H+/ATP ratio) was investigated in membrane vesicles from a Synechocystis 6803 mutant in which the serine at position 37 in the hydrophilic loop of the c-subunit from the wild type was replaced by a negatively charged glutamic acid residue (strain plc37). At this position the c-subunit of chloroplasts and the cyanobacterium Synechococcus 6716 already contains glutamic acid. H+/ATP ratios were determined with active ATP synthase in thermodynamic equilibrium between phosphate potential (deltaGp) and the proton gradient (deltamuH+) induced by acid-base transition.

CTP:phosphocholine cytidylyltransferase and protein kinase C recognize different physical features of membranes: differential responses to an oxidized phosphatidylcholine.

Protein kinase C (PKC) and CTP:phosphocholine cytidylyltransferase (CT) are two examples of enzymes that are regulated by reversible binding to membranes, and this binding is influenced by membrane physical properties. CT activation by oxidized phosphatidylcholines was recently demonstrated and was linked to the acyl chain disordering effect of the oxidized species (Biochemistry 38, 15606). In this paper, we compare the responses of PKC and CT to an oxidized PC, and investigate the physical properties of lipid bilayers that modulate the activity of these enzymes.