Water and nonelectrolyte permeability of lipid bilayer membranes

Both the permeability coefficients (Pd's) through lipid bilayer membranes of varying composition (lecithin [L], lecithin:cholesterol [LC], and spingomyelin:cholesterol [SC]) and the n-hexadecane:water partition coefficients (Knc's) of H2O and seven nonelectrolytes (1,6 hexanediol, 1,4 butanediol, n-butyramide, isobutyramide, acetamide, formamide, and urea) were measured. For a given membrane compositiin, Pd/DKnc (where D is the diffusion constant in water) is the same for most of the molecules tested. There is no extraordinary dependence of Pd on molecular weight; thus, given Pd(acetamide), Pd(1,6 hexanediol) is correctly predicted from the Knc and D values for the two molecules. The major exceptions are H2O, whose value of Pd/DKnc is about 10-fold larger, and urea, whose value is about 5-fold smaller than the general average. In a "tight" membrane such as SC, Pd(n-butyramide)/Pd(isobutyramide)=2.5; thus this bilayer manifests the same sort of discrimination between branched and straight chain molecules as occurs in many plasma membranes. Although the absolute values of the Pd's change by more than a factor of 100 in going from the tightest membrane (SC) to the loosest (L), the relative values remain approximately constant. The general conclusion of this study is that H2O and nonelectrolytes cross lipid bilayer membranes by a solubility-diffusion mechanism, and that the bilayer interior is much more like an oil (a la Overton) than a rubber-like polymer (a la Lieb and Stein).

Permeability of dog lung endothelium to sodium, diols, amides, and water

Bolus injection of T-1824-albumin, test indicator, and tritiated water into a jugular vein of the anesthetized dog and sequential sampling of blood from a carotid artery yielded multiple-indicator outflow patterns for the lung. Permeability-surface products of the test indicator for the lung endothelial barrier were obtained by comparison of test indicator with T-1824-albumin on the upslope of the test-indicator curve and correction for backdiffusion. The derived endothelial permeability coefficients, based on surface area/wet lung weight-500 cm2/g (mean +/- 2 SE, 10(-5) cm s(-1)), were: sodium ion, 2.9 +/- 0.8; ethylene glycol, 7.3 +/- 1.5; 1, 3-propranediol, 7.9 +/- 3.2; 1, 2-propanediol, 10 +/- 4; 1, 4-butanediol, 14 +/- 8; 1, 5-pentanediol, 21 +/- 6; 1, 6-hexanediol, 41 +/- 11; formamide, 16 +/- 9; acetamide, 13 +/- 4; propionamide, 31 +/- 12; butyramide, 42 +/- 24; valeramide, 79 +/- 12; tritiated water, 150 +/- 50. The backdiffusion correction varies from 8% for sodium to 75% for valeramide. A parallel-pathway model of blood-tissue passive exchange of small nonelectrolyte solutes is compatible with these results, with a lipid pathway through endothelial cells and an aqueous pathway possibly through interendothelial clefts.

Permeability pathways for non-electrolytes through Bufo bufo gall-bladder

Amphotericin B treatment increases the thiourea, D-xylose and mannitol fluxes and lowers those of urea, N-methyl-urea, acetamide, formamide, and N-N'-dimethyl-thiourea. The degree of flux inhibition is related to the cellular permeability of these compounds. Most probably Amphotericin B increases the permeability of all those molecules across the luminal plasma membrane, but simultaneously elicits a cellular swelling, which reduces the diffusion across the lateral plasma membranes. This effect masks the polyene effect especially for molecules showing a mainly cellular permeation pathway such as amides and lipid soluble molecules.

Red cell membrane permeability deduced from bulk diffusion coefficients

The permeability coefficients of dog red cell membrane to tritiated water and to a series of[(14)C]amides have been deduced from bulk diffusion measurements through a "tissue" composed of packed red cells. Red cells were packed by centrifugation inside polyethylene tubing. The red cell column was pulsed at one end with radiolabeled solute and diffusion was allowed to proceed for several hours. The distribution of radioactivity along the red cell column was measured by sequential slicing and counting, and the diffusion coefficient was determined by a simple plotting technique, assuming a one-dimensional diffusional model. In order to derive the red cell membrane permeability coefficient from the bulk diffusion coefficient, the red cells were assumed to be packed in a regular manner approximating closely spaced parallelopipeds. The local steady-state diffusional flux was idealized as a one-dimensional intracellular pathway in parallel with a one-dimensional extracellular pathway with solute exchange occurring within the series pathway and between the pathways. The diffusion coefficients in the intracellular and extracellular pathways were estimated from bulk diffusion measurements through concentrated hemoglobin solutions and plasma, respectively; while the volume of the extracellular pathway was determined using radiolabeled sucrose. The membrane permeability coefficients were in satisfactory agreement with the data of Sha'afi, R. I., C. M. Gary-Bobo, and A. K. Solomon (1971. J. Gen. Physiol. 58:238) obtained by a rapid-reaction technique. The method is simple and particularly well suited for rapidly permeating solutes.

Microbial metabolism of the pyridine ring. The metabolism of pyridine-3,4-diol (3,4-dihydroxypyridine) by Agrobacterium sp

1. Pyridine-3,4-diol (3,4-dihydroxypyridine, 3-hydroxypyrid-4-one), an intermediate in 4-hydroxypyridine metabolism by an Agrobacterium sp (N.C.I.B. 10413), was converted by extracts into 1mol of pyruvate, 2mol of formate and 1mol of NH(3) at pH7.0. 2. Formate, but not the alternative likely product formamide, was further oxidized fivefold faster by 4-hydroxypyridine-grown washed cells than by similar organisms grown on succinate. 3. The oxidation of pyridine-3,4-diol by crude extracts at pH8.5 required 1mol of O(2)/mol of substrate, produced 1mol of acid and led to the formation of formate and a new compound with an extinction maximum of 285nm (Compound I). This step was believed to be mediated by a new labile dioxygenase (t((1/2))=4h at pH7.0, 4 degrees C) cleaving the pyridine ring between C-2 and C-3. 4. Many of the properties of this pyridine-3,4-diol dioxygenase paralleled those of the extradiol (;meta') oxygenases of aromatic-ring cleavage. The extreme lability of the enzyme has so far precluded extensive purification. 5. Compound I showed changes in the u.v.-absorption spectrum with pH but after acidification it was converted into a new product, 3-formylpyruvate, with an extinction maximum now at 279nm. 6. Both Compound I and 3-formylpyruvate were metabolized by extracts but at very different rates. The slower rate of metabolism of Compound I was nevertheless consistent with that of pyridine-3,4-diol metabolism. 7. On acidification Compound I released about 0.65mol of NH(3) and has been identified as 3-formiminopyruvate. 8. 3-Formylpyruvate was hydrolysed to formate and pyruvate (K(m) 2mum) by an acylpyruvate hydrolase active against several other dioxo homologues. The activity of this enzyme was much lower in extracts of succinate-grown cells.

Oxaluric acid: a non-metabolizable inducer of the allantoin degradative enzymes in Saccharomyces cerevisiae

Saccharomyces cerevisiae degrades allantoin in five steps to ammonia, CO(2), and glyoxylate. Previously we demonstrated that allophanic acid, the last intermediate of the pathway, was required for induction of all five degradative enzymes. The data presented here indicate that oxaluric acid, an allophanate analogue, is capable of serving as a non-metabolizable inducer. Oxaluric acid brings about a high level of induction even in strains lacking urea carboxylase. Induction observed with parabanic acid was found to result from its spontaneous breakdown to oxaluric acid.

Bacterial degradation of nitrilotriacetic acid (NTA)

Pseudomonas sp. was isolated from sewage effluent by elective culture with nitrilotriacetic acid (NTA) as its sole nitrogen and carbon source for growth. NTA-nitrogen was converted to biomass and ammonium by growing cultures with small quantities of nitrite (< 1 ppm) being produced. Washed cell suspensions degraded all of the NTA-nitrogen to ammonium before total conversion of the NTA-carbon to carbon dioxide and water. Resting cell suspensions grown from NTA oxidized NTA, aminodiacetic acid, and glycine immediately, whereas methylaminodiacetic acid was oxidized only after an adaptive lag period, and sarcosine was not oxidized at all. Oxidation of aminodiacetic acid was always more rapid than NTA. Nitrosamines or other nitroso compounds were not found in culture or resting cell supernatants incubated with NTA.

Permeability of red cell membranes to small hydrophilic and lipophilic solutes

The permeability coefficients of a series of amides, ureas, and diols have been measured on red cells of man and dog using the minimum volume method of Sha'afi et al. When the molecules are grouped according to their ether-water partition coefficients, k(ether), the behavior of the hydrophilic molecules, with k(ether) less than water, is different from that of the lipophilic molecules, characterized by k(ether) greater than water. The rate of permeation of the hydrophilic molecules through an aqueous pathway is determined by the molar volume, a parameter in which the geometrical measure of molecular volume is modified by hydrogen-bonding ability. This indicates the importance of chemical interactions within the aqueous path. The permeation of the lipophilic molecules is determined in the first instance by k(ether), taken as a measure of the ease with which the molecule can escape from its aqueous environment. Within the membrane, lipophilic permeability is modified both by steric factors and by the formation of hydrogen bonds with membrane components. These data allow one to infer that lipid-soluble molecules travel through an organized structure within the lipid membrane and come into contact with polar moieties.