Primary current-sensing noise thermometry in the millikelvin regime.

The use of low-temperature platforms with base temperatures below 1 K is rapidly expanding, for fundamental science, sensitive instrumentation and new technologies of potentially significant commercial impact. Precise measurement of the thermodynamic temperature of these low-temperature platforms is crucial for their operation. In this paper, we describe a practical and user-friendly primary current-sensing noise thermometer (CSNT) for reliable and traceable thermometry and the dissemination of the new kelvin in this temperature regime. Design considerations of the thermometer are discussed, including the optimization of a thermometer for the temperature range to be measured, noise sources and thermalization. We show the procedure taken to make the thermometer primary and contributions to the uncertainty budget. With standard laboratory instrumentation, a relative uncertainty of 1.53% is obtainable. Initial comparison measurements between a primary CSNT and a superconducting reference device traceable to the PLTS-2000 (Provisional Low Temperature Scale of 2000) are presented between 66 and 208 mK, showing good agreement within the k=1 calculated uncertainty.

Determining double-bond positions in monoenoic 2-hydroxy fatty acids of glucosylceramides by gas chromatography-mass spectrometry.

We applied a gas chromatography-mass spectrometry (GC-MS) method using dimethyl disulfide (DMDS) adducts and were able to determine the double-bond positions in monounsaturated 2-hydroxy fatty acids (2-HFA). 2-HFA methyl esters, prepared from the hydrolysate of Arabidopsis thaliana leaf glucosylceramides, were acetylated and methylthiolated. GC-MS analysis of the resulting DMDS adducts showed simple mass spectra with recognizable molecular ions and a series of key fragment ions indicating the original double-bond positions in the aliphatic chain. Based on this GC-MS elucidation, we confirmed that Arabidopsis leaf glucosylceramides have C22, C23, C24, C25, and C26 chain length 2-HFA with monounsaturation, and all their double bonds are placed at the n-9 position. This procedure is simple, time efficient, and highly sensitive.

Identification of activities that catalyze the cis-trans isomerization of the double bond of a mono-unsaturated fatty acid in Pseudomonas sp. strain E-3.

A cell-free extract of Pseudomonas sp. strain E-3 catalyzed the conversion of 9-cis-hexadecenoic acid [16:1(9c)] to 9-trans-hexadecenoic acid [16:1(9t)] in the free acid form and when 16:1(9c) was esterified to phosphatidylethanolamine (PE). The cytosolic fraction catalyzed the isomerizations of free 16:1(9c) by itself and of 16:1(9c) esterified to PE in the presence of the membrane fraction. Tracer experiments using [2,2-2H2]16:1(9c) demonstrated that the isomerization of free 16:1(9c) occurred independently of the isomerization of 16:1(9c) esterified to PE, indicating that this bacterium has two types of activities that catalyze the cis-trans isomerization of the double bond of a mono-unsaturated fatty acid.

An improved method for rapid analysis of the fatty acids of glycerolipids.

An improved rapid procedure to determine the fatty acid composition of glycerolipids is described. The procedure includes KOH-catalyzed transesterification and high-speed gas chromatography. Glycerolipids (20-40 mg) were mixed with 2 mL of hexane and 0.2 mL of 2 M methanolic KOH at room temperature for 1-2 min. The fatty acid methyl esters in the hexane layer were analyzed by gas chromatography on 10% SP-2340 at 240 degrees C. Methyl linolenate and docosahexaenoate eluted within 2 and 5 min, respectively. Analysis was thus completed within 5 min for common vegetable oils and 8 min for fish oils.

cis-9,cis-15-octadecadienoic acid: a novel fatty acid found in higher plants.

An unusual fatty acid, cis-9,cis-15-octadecadienoic acid, has been identified in the pulp lipids of mango (Mangifera indica L.) grown in the Philippines. To our knowledge, the occurrence of cis-9,cis-15-octadecadienoic acid in higher plant lipids has not been previously reported. The structure confirmation was based on the results of chromatographic (capillary GC, argentation thin-layer) and spectrometric (GC-MS, infrared, ultraviolet) analysis and chemical treatment. This butylene-interrupted dienoic fatty acid is concentrated in the pulp part of mango fruit and occupies 5.4% of total acyl groups in the pulp lipids; whereas a common octadecadienoic acid, linoleic acid, is a minor component (1.1%) in the same lipids. If a trivial name is desired, it is suggested that cis-9,cis-15-octadecadienoic acid be called "mangiferic" acid.

The relationship between induction of peroxisomal beta-oxidation and long-chain fatty acid composition in rat liver.

The long-chain fatty acid composition in rat liver, by which peroxisomal beta-oxidation system was induced, was analyzed in vitro and in vivo. In primary culture of hepatocytes, treatment with 0.4 mM clofibrate or long-chain fatty acids caused an increase in the peroxisomal beta-oxidation activity, in addition the oleic acid [18:1(n-9)] content in the cells was increased two-fold by addition of very long-chain fatty acids to the culture medium, but clofibrate had no effect. A two-fold of increase in 18:1(n-9) content was observed in the hepatic subcellular fractions from rats fed a diet containing 0.25% clofibric acid. The ratio of cis-vaccenic acid [18:1(n-7)] to total 18:1 content decreased by more than half compared with control in clofibric acid treated liver. The level of 18:1(n-7) was not changed in all experiments. It is suggested that perturbation of C-18 chain length fatty acids occurs in peroxisomal beta-oxidation induced liver.

Evidence for cis-trans isomerization of a double bond in the fatty acids of the psychrophilic bacterium Vibrio sp. strain ABE-1.

Vibrio sp. strain ABE-1 was grown in a medium that contained as its stable isotope tracer either [2,2-2H2]cis-9-hexadecenoic or [2,2-2H2]trans-9-hexadecenoic acid. Gas chromatographic-mass spectrometric analysis of the cis-9-hexadecenoic and trans-9-hexadecenoic acid fractions from the cells revealed the formation of an intracellularly isomerized 2,2-2H2-fatty acid which differed from the tracer only in the geometrical configuration of the double bond. This observation shows that cis-trans isomerization without a shift in double-bond position between these two geometric hexadecenoic acid isomers can occur in the cells.

Novel pathways of oleic and cis-vaccenic acid biosynthesis by an enzymatic double-bond shifting reaction in higher plants.

The novel pathways of oleic acid formation from cis-vaccenic (cis-11-octadecenoic) acid and of cis-vaccenic acid formation from oleic acid by enzymatic positional isomerization have been proposed in higher plants, based on stable-isotope experiments using [2,2-2H2]cis-vaccenate or [2,2-2H2]oleate as an immediate precursor. A pulp homogenate and also pulp slices prepared from developing kaki (Diospyros kaki) fruit could catalyze these hitherto unknown isomerizations. This suggests the presence of a new type of isomerase responsible for the double-bond shifting reaction without cis-trans isomerization in the middle of fatty acid carbon chains.