Effects of metabolized and unmetabolized arachidonate on rat platelet shape change

Arachidonate (0.12-1.5 mM) initiated a concentration-dependent, saturable shape change of rat platelets suspended in citrated plasma. Interaction of arachidonate with platelets led to the formation of active metabolites that appeared to be the actual inducers of shape change. Among these, prostaglandin endoperoxides rather than thromboxane A2 seemed necessary for shape change. No role of the products of the lipoxygenase pathway could be shown. In the presence of cyclooxygenase and lipoxygenase inhibitors, arachidonate (0.25-0.5 mM) prevented platelet shape change induced by the endoperoxide analog U-46619 but not by other agonists such as ADP or serotonin. Arachidonate acts therefore as both an agonist and an antagonist of platelet shape change. The agonistic effect requires arachidonate metabolism while the antagonistic activity seems to be linked to the fatty acid molecule itself.

Inhibition of Phytophthora cactorum by a bacterial antagonist

Bacterial iolate B8 inhibited the growth of six isolates of Phytophthora cactorum on cornmeal agar. Under greenhouse conditions, B8 reduced infections by three isolates of P. cactorum in sterile field soil. Growth of P. cactorum on cornmeal agar was completely inhibited with 40% autoclaved B8 extract. The growth was significantly reduced by low pH alone (pH 4.5 or less) but even when the pH of B8 extract was raised to 6, P. cactorum growth was completely inhibited. Cornmeal agar buffered with 15 mM citrate, pH 5, was suitable for assaying extracts for antagonism to P. cactorum. Acetic acid and other fatty acids (possible metabolites of B8) were also inhibitory, with degree of antibiosis increasing with the size of the fatty acid molecule. The antibiotic produced by B8 was characterized as neutral (not absorbed by ion exchange resins) and of low molecular weight.

Uptake of N-(9-Anthroyloxy) Fatty Acid Fluorescent Probes Into Lipid Bilayers

A description in thermodynamic terms is given of ligand-membrane interaction which may occur by either or both a binding and a partition process. Results obtained by fluorescence enhancement and polarization techniques on the uptake of n-(9-anthroyloxy) fatty acids by phospholipid bilayers are analysed to show that binding rather than partition effects primarily determine the extent of probe uptake. Liposome concentration-dependence effects are also reported which required that binding results obtained with different probes be compared at fixed lipid concentrations. On this basis it is concluded that as the separation of the anthracene and carboxyl groups within the fatty acid molecule is increased, and hence as the anthracene group moves deeper into the bilayer, the fluorescent probe is bound to the bilayer with greater affinity but is accepted by fewer binding sites within the membrane. Studies on probe uptake at high ionic strength and into negatively charged bilayers indicate that hydrophobic rather than electrostatic interactions make the dominant contribution to the free energy of binding.

An optical method of measuring the thickness of adsorbed monolayers

The interferometric techniques developed by Tolansky have been used to study films adsorbed on solid surfaces. A monomolecular layer of fatty acid was spread by the retraction technique over part of a selected facet of a piece of mica. A highly reflecting layer of silver was then deposited on both sides of the mica specimen, and the thickness of the acid layer determined by multiple reflexion interferometry. The values so obtained were in agreement with X-ray data on the length of the fatty-acid molecule. Examination showed that the layers were uniform in thickness; polymolecular layers were absent. The method provides direct and independent evidence that molecules of a fatty acid, spread by the retraction technique, are adsorbed on a solid surface as a uniform monomolecular layer.