Uncoupling action of amytal in membrane vesicles from Escherichia coli

Enigmatic effect of cellular ATP on fatty acid biosynthesis. Stimulation by moderate decrease and inhibition by increase of cellular ATP

The cellular ATP concentration was tested for its effect on fatty acid biosynthesis from glucose in hepatocytes. ATP was manipulated by adding increasing concentrations of cycloheximide, amytal, atractyloside, 2,4-dinitrophenol or adenosine. A slight decrease in cellular ATP coincided with a stimulation of fatty acid biosynthesis whereas a further lowering of cellular ATP resulted in a gradual inhibition. Increasing the cellular ATP level by titration with adenosine had the opposite effect. These results are in line with the suggestion that fatty acid biosynthesis from glucose is an energy-yielding process which is stimulated by a moderate drop in cellular ATP.

Proline dehydrogenase from Escherichia coli K12. Properties of the membrane-associated enzyme

We have examined the oxidative activities of inverted cytoplasmic membrane preparations from Escherichia coli bearing proline dehydrogenase. Our measurements include both direct substrate:2,6-dichloroindophenol and substrate:O2 oxidoreductase assays and the 9-aminoacridine fluorescence assay for proton translocation, employing succinate and NADH dehydrogenases as comparative standards. Our data show the following. (a) Membranes prepared in a new buffer system bear proline dehydrogenase that is stable in both activity and membrane association. This membrane-associated enzyme shows an apparent Km for proline 20-fold lower than that estimated from the solubilized and purified enzyme. (b) Electrons are transferred from proline to O2 via the respiratory chain since proline utilization requires porphyrin synthesis and it is coupled to trans-membrane proton translocation. (c) Patterns of inhibition by 5-ethyl-5-isopentyl barbituric acid (Amytal) and 2-heptyl-4-hydroxyquinoline-N-oxide (HpHOQnO) suggest that parallel pathways of electron flux from NADH and proline converge at a cyanide-sensitive terminal oxidase. Succinate:O2 and succinate:DCIP oxidoreductase activities are stimulated by HpHOQnO and Amytal, and the former is inhibited by cyanide in this system. (d) Amytal is a non-competitive inhibitor of proline dehydrogenase. (e) Analysis of our fluorescence data suggests that Amytal and HpHOQnO dissipate delta pH at concentrations as low as 5 mM and 8.5 microM, respectively, in this system.

Transport of organic ions through lipid bilayers. The barbiturates

In a previous article [Naunyn-Schmiedeberg's Arch Pharmacol (1981) 316:266-272] transport of a number of organic ions across lipid bilayers was investigated using single bilayer liposomes. In this investigation the translocation of structurally closely related barbiturates across lipid bilayers is studied. The anionic form of the barbiturates can pass lipid bilayers, provided that the lipophilicity of the 5,5-disubstituted side chain is high enough. This permeability of barbiturates in the ionized form explains their uncoupling action of the oxidative phosphorylation and the deviations from the pH-partition theory found in absorption processes.

Transport of organic ions through lipid bilayers

The transport of a series of charged drugs and other organic ions through lipid bilayers was studied, using single-bilayer liposomes. Monovalent organic cations and organic anions could carry charge into the liposomes independent of the nature of their counter ion. Ion-pair formation, following the addition of an excess of I- or Br-, did not facilitate this transport. However the passage of organic cations and anions across the membrane required the presence of the organic anion tetraphenylborate in the lipid bilayer. This effect of tetraphenylborate is probably due to a lowering of an intra-membrane potential energy hill, the principal barrier for transport, and not to ion-pair formation. It is concluded that organic ions that possess sufficiently lipophilic structures to mask their charged character, can pass lipid bilayers in charged form.