The carbon isotope composition (␦ 13 C) of CO 2 produced in darkness by intact French bean (Phaseolus vulgaris) leaves was investigated for different leaf temperatures and during dark periods of increasing length. The ␦ 13 C of CO 2 linearly decreased when temperature increased, from Ϫ19‰ at 10°C to Ϫ24‰ at 35°C. It also progressively decreased from Ϫ21‰ to Ϫ30‰ when leaves were maintained in continuous darkness for several days. Under normal conditions (temperature not exceeding 30°C and normal dark period), the evolved CO 2 was enriched in 13 C compared with carbohydrates, the most 13 C-enriched metabolites. However, at the end of a long dark period (carbohydrate starvation), CO 2 was depleted in 13 C even when compared with the composition of total organic matter. In the two types of experiment, the variations of ␦ 13 C were linearly related to those of the respiratory quotient. This strongly suggests that the variation of ␦ 13 C is the direct consequence of a substrate switch that may occur to feed respiration; carbohydrate oxidation producing 13 C-enriched CO 2 and ␤-oxidation of fatty acids producing 13 C-depleted CO 2 when compared with total organic matter (Ϫ27.5‰). These results are consistent with the assumption that the ␦ 13 C of dark respired CO 2 is determined by the relative contributions of the two major decarboxylation processes that occur in darkness: pyruvate dehydrogenase activity and the Krebs cycle.Photosynthetic CO 2 assimilation of C 3 plants discriminates against 13 CO 2 so that organic matter is, on average, 20‰ depleted in 13 C compared with atmospheric carbon dioxide (for recent review, see Brugnoli and Farquhar, 2000). Respiratory carbon fluxes in light (i.e. photorespiration and "day" respiration) are often assumed to be negligible or weakly fractionating processes. However, the carbon isotope signature of organic matter may be modified by nighttime respiration depending on the ␦ 13 C of the evolved CO 2 because respiratory carbon lost by many plants has been shown to be within 30% to 60% of the carbon fixed through photosynthesis (Evans, 1993; Amthor, 2000).In vitro studies using protoplasts have shown that respired CO 2 isotope composition is identical to that of the Suc supplied to the culture medium, indicating that no fractionation occurs during respiration in the dark (Lin and Ehleringer, 1997). A similar result was also obtained in long-term experiments with animals, where the isotope composition of CO 2 expired by mice (Mus musculus) reflected that of the diet (Perkins and Speakman, 2001). In contrast, it has been shown previously that CO 2 produced by respiration in the dark is 6‰ 13 C enriched when compared with Suc in intact French bean (Phaseolus vulgaris) leaves (Duranceau et al., 1999). Similar results were also obtained in Nicotiana sylvestris and sunflower (Helianthus annuus), although CO 2 was less 13 C enriched with ␦ 13 C values of 4‰ and 3‰, respectively (Ghashghaie et al., 2001). Moreover, it has been demonstrated that the ␦ 13 C value of CO 2 evolved in the dar...

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microorganisms of human skin fl ora, triglycerides are partially hydrolyzed, producing FFAs, diglycerides, monoglycerides, and glycerol ( 10-12 ). In addition, continual removal of the uppermost layer of the skin leads to liberation, at the skin surface, of free and esterifi ed cholesterols along with FFAs. Several lipid classes are then present in SSLs, and the complexity of the mixture is emphasized by the structural microheterogeneity within each class.Hydrolipidic fi lm represents an important modulator of cutaneous barrier functions ( 1-5 ), particularly in SC hydration. Moreover, sebum transports antioxidants to the skin surface (e.g., vitamin E), preventing aging ( 3,13,14 ). Free fatty acids contribute to the pH of skin surface ( 15-17 ). A particular acid (sapienic acid, C16:1 ⌬ 6) exhibits strong innate antimicrobial activity ( 18 ). Sebaceous lipids are involved in some infl ammatory diseases such as acne ( 14,19 ), seborrhea, or dermatitis ( 13 ). Maintaining the stability of the amounts and composition of SSL is of major importance to preserving skin barrier properties. Moreover, information provided by SSL analyses, such as fi ne profi ling, squalene/cholesterol ratio, and intact glyceride patterns, contribute to the wide knowledge of physiological and pathological evolution of hydrolipidic fi lm.Our study falls within the framework of lipidomics, in which global SSLs profi les are determined in the entire sample, keeping the structural integrity of the compounds. Our purpose was to develop a simple analytical protocol using a noninvasive sampling method without timeconsuming sample preparation steps that would provide a qualitative characterization of individual SSL compounds and a quantitative evaluation of different lipid classes. SSLs are formed from a complex mixture of free fatty acids (FFAs) and neutral lipids arising from both sebaceous secretion and skin removal ( 6 ). Freshly liberated sebum contains predominantly triglycerides, wax esters, and squalene ( 7-9 ). Under the infl uence of lipase-producing Abbreviations: APCI, atmospheric pressure chemical ionization; CI, chemical ionization; EI, electron impact; FID, fl ame ionization detector; HTGC-MS, high-temperature gas chromatography-mass spectrometry; SC, stratum corneum; SSL: skin surface lipid; TIC, total ion current.

Gas chromatography-mass spectrometry has been used to determine the nature of organic materials used in mummification balms. A comparative analysis of samples taken from Egyptian mummies is developed. The results are given in two parts. First, it is shown that the chemical composition of the balm is practically independent of the part of the mummy from which it is taken. This study was done on a Ptolemaic mummy (circa 100 BC from the Guimet Museum in Lyon). Fats, beeswax, and diterpenic resins were the main components: they were found everywhere. Castor oil was also very often detected (in half of the samples). This particular fat is present in the balm inside the thorax but not in the skull. Moreover it is shown that a vegetable tannin was employed. Components indicative of vegetable tannin input (gallic acid and inositols) were found in seven samples out of eighteen, particularly close to the body and on the canopic pack of the heart. Secondly, some conclusions from a comparative study of the composition of balms from mummies of various social levels as well as of different Egyptian periods are reported. It is shown that beeswax was used as from very early times (XVIIIth dynasty). The mixture of beeswax, fats, and diterpenoid resins would appear to be more recent. The balms of three mummies dating from more recent Egyptian periods (XIXth to XXVth dynasty) were analysed. No evidence of a resin, gum-resin, or plant gum could be found. Some mummies would appear to have been embalmed with fats or beeswax. Finally, the entrails canopic pack said to belong to Ramses II undoubtedly shows an embalming process with a triterpenic resin of the mastic type. The adopted analytical methodology enabled us to achieve simultaneous detection of four components of the balm of the Ptolemaic mummy. Analysis of the other five mummies revealed far less complex chemical compositions for the balms. This may be an indication of different embalming processes, although we should bear in mind the question of organic matter preservation through the ages.

The natural (13)C/(12)C isotope composition (delta(13)C) of plants and organic compounds within plant organs is a powerful tool to understand carbon allocation patterns and the regulation of photosynthetic or respiratory metabolism. However, many enzymatic fractionations are currently unknown, thus impeding our understanding of carbon trafficking pathways within plant cells. One of them is the (12)C/(13)C isotope effect associated with invertases (EC 3.2.1.26) that are cornerstone enzymes for Suc metabolism and translocation in plants. Another conundrum of isotopic plant biology is the need to measure accurately the specific delta(13)C of individual carbohydrates. Here, we examined two complementary methods for measuring the delta(13)C value of sucrose, glucose and fructose, that is, off-line high-performance liquid chromatography (HPLC) purification followed by elemental analysis and isotope ratio mass spectrometry (EA-IRMS) analysis, and gas chromatography-combustion (GC-C)-IRMS. We also used these methods to determine the in vitro (12)C/(13)C isotope effect associated with the yeast invertase. Our results show that, although providing more variable values than HPLC approximately EA-IRMS, and being sensitive to derivatization conditions, the GC-C-IRMS method gives reliable results. When applied to the invertase reaction, both methods indicate that the (12)C/(13)C isotope effect is rather small and it is not affected by the use of heavy water (D(2)O).

The aim of this study was to use headspace solid phase microextraction (SPME) to reveal the presence of resin in archaeological samples, such as mummification balms, from ancient Egypt. Experiments were first performed with fresh resins of known origin. The SPME fibre readily extracted mono- and sesquiterpenes and, to a lesser extent, diterpenes. Using mass spectra and retention indices of constitutive compounds, qualitative analysis of the volatile fraction allowed us to differentiate resins or gum-resins such as myrrh, olibanum, galbanum, labdanum, mastic, and conifer resins. SPME was then successfully applied to archaeological samples from ancient Egypt in which the presence of resins was detected. Volatile components were desorbed and trapped according to the same SPME procedure as was applied to fresh resins, after a sample preparation consisting of a fine grinding.