Membrane formation, autocatalytic

Let us recall the micellar aqueous system, as this procedure is actually the basic one. The chemistry is based on fatty acids, that build micelles in higher pH ranges and vesicles at pH c. 8.0-8.5 (Hargreaves and Deamer, 1978a). The interest in fatty acids lies also in the fact that they are considered possible candidates for the first prebiotic membranes, as will be seen later on. The experimental apparatus is particularly simple, also a reminder of a possible prebiotic situation the water-insoluble ethyl caprylate is overlaid on an aqueous alkaline solution, so that at the macroscopic interphase there is an hydrolysis reaction that produces caprylate ions. The reaction is very slow, as shown in Figure 7.15, but eventually the critical micelle concentration (cmc) is reached in solution, and thus the first caprylate micelles are formed. Aqueous micelles can actually be seen as lipophylic spherical surfaces, to which the lipophylic ethyl caprylate (EC) avidly binds. The efficient molecular dispersion of EC on the micellar surface speeds up its hydrolysis, (a kind of physical micellar catalysis) and caprylate ions are rapidly formed. This results in the formation of more micelles. However, more micelles determine more binding of the water-insoluble EC, with the formation of more and more micelles a typical autocatalytic behavior. The increase in micelle population was directly monitored by fluorescence quenching techniques, as already used in the case of the... 

Several hematologists are of the view that the primary step in hemostasis is the adhesion of platelets to exposed collagen fibers. " It has been proposed that the adhesion is due to the formation of an enzyme-acceptor complex between the incomplete carbohydrate chains (galactosyl residues) of collagen and an enzyme of the platelet membrane (glycosyl transferase). Platelets in contact with collagen fibers contract and release adenosine diphosphate (ADP) as well as other platelet constituents. ADP causes more platelets to adhere and the autocatalytic reaction proceeds towards the formation of a hemostatic plug. 

Halomethyl compounds are subdivided into monohalomethyls, which are alkylating agents, and polyhalomethyls, which must be metabolized to an ultimate species. Reductive dechlorination of carbon tetrachloride 353) to chloroform by rabbit liver microsomes parallels the concentration of cytochrome P-450 in the microsomes but requires anaerobic conditions and NADPH. The identification of hexachloroethane after incubation of NADPH-reduced microsomes with carbon tetrachloride is indicative of homolytic formation of the free radicals of chlorine and trichloromethyl and supports the hypothesis that such species initiate an autocatalytic peroxidation of lipid membranes that results in the observed hepatotoxicity. A similar scheme for radical formation and lipid destruction has been described by Reynolds and Moslen for halothane. In contrast to the reductive dechlorination of carbon tetrachloride, the metabolism of chloroform to carbon dioxide in vitro requires oxygen and produces carbonyl chloride (phosgene) as an intermediate. That this also... 

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