In human fibroblasts, triacylglycerols are degraded in two separate and independent subcellular (lysosomal and cytoplasmic non-lysosomal) compartments(1) . In the lysosomal compartment, triacylglycerols and cholesteryl esters of low density lipoprotein and very low density lipoprotein taken up by cells are degraded by the acid lysosomal lipase(2, 3) , which is genetically deficient in Wolman disease(4) . In the cytoplasmic compartment of fibroblasts, triacylglycerols are degraded by a lipase system (yet poorly characterized) different from the other known cellular (hormone-sensitive lipase) or secretory lipases (1, 5) and different from the cholesteryl ester degradation pathway(6) . As shown by using radiolabeled oleic acid or pyrene-containing fluorescent fatty acids, this degradative pathway of cytoplasmic triacylglycerols is deficient in the neutral lipid storage disease (NLSD)()(1, 5, 7, 8, 9, 10) , a rare inherited metabolic disease generally characterized by the association of muscular weakness, ichthyosis, and multisystemic triacylglycerol storage(11, 12) . We have recently reported that the pool of cytoplasmic triacylglycerols accumulated in fibroblasts from neutral lipid storage disease is constituted by triacylglycerols endogenously biosynthesized (7, 8, 9, 10) and by triacylglycerols taken up from high density lipoproteins(13) . An increased biosynthesis of phosphatidylethanolamine has also been reported(14) .

Comparative studies of the uptake and metabolic utilization of short-chain and long-chain fluorescent pyrene fatty acids in cultured lymphoblasts (15) and in fibroblasts (16) have shown that short-chain (pyrene-butanoic) acid was incorporated into phospholipids but not in triacylglycerols, whereas long-chain (pyrene-decanoic and pyrene-dodecanoic) fatty acids were incorporated into phospholipids and triacylglycerols. In lymphoblasts from neutral lipid storage disease pulsed with short-chain pyrene fatty acid, we detected no significant accumulation of fluorescent triacylglycerols(15) . These results led us to speculate that replacing natural long-chain fatty acids by short-chain fatty acids could be of interest to slow down the triacylglycerol accumulation in neutral lipid storage disease cells. However, the conclusions obtained with fluorescent pyrene fatty acids cannot be directly transposed to natural fatty acids because natural and pyrene fatty acids exhibited several known metabolic differences (5, 8, 17) . The apparent lack of incorporation of short-chain fluorescent fatty acid (pyrene-butanoic) in triacylglycerols and of accumulation of pyrene-butanoic containing triacylglycerols in NLSD cells could be due either to a lack of biosynthesis of pyrene-butanoic-containing triacylglycerols (despite the biosynthesis of pyrene-butanoic-containing glycerophospholipids) or to a rapid degradation of pyrene-butanoic-containing triacylglycerols by a cytoplasmic pathway independent of the neutral lipase system (deficient in intact NLSD cells). This latter hypothesis is supported by the existence in fibroblast homogenates of five different enzymes able to hydrolyze in vitro long- or short-chain fluorescent triacylglycerols. Both groups of enzymes referred to as long-chain lipases or short/medium-chain lipases, respectively, can be discriminated by their enzymatic properties (heat stability, effect of inhibitors)(1, 18) , with short/medium-chain lipases exhibiting properties of (nonspecific) carboxylesterases(19) .

This prompted us to investigate the metabolism of short- and long-chain fatty acids in cultured fibroblasts from controls and from neutral lipid storage disease to examine the metabolic fate of short-chain fatty acids and their potential influence on the triacylglycerol accumulation in neutral lipid storage disease.

The data reported here showed that, in comparison to long-chain fatty acids, short/medium-chain fatty acids 1) are incorporated into cellular lipids at a much lower rate, 2) induce a lower accumulation of triacylglycerols in NLSD cells, and 3) contained in triacylglycerols are hydrolyzed at a normal rate through a catabolic pathway involving a short/medium-chain lipase activity not deficient in situ in NLSD cells (in contrast to the defect of the long-chain lipase activity).

MATERIALS AND METHODS

Chemicals

Cell Cultures

Cell viability was assessed by 3-(4,5-dimethyl thiazol-2-yl)-2,5diphenyl tetrazolium bromide test (20) or by trypan blue test and by morphological examination as previously used (21) , which shows that the number of necrotic and apoptotic cells did not exceed 8-10% during the metabolic experiments.

Pulse-Chase Experiments with Fatty Acids

Cells were pulsed with fatty acids, used at the concentrations indicated in the text, generally 30 nmol/ml and 10 dpm, solubilized in MeSO (0.5% final concentration), and preincubated with the culture medium (for 30 min at 37 °C) before addition to the cell culture. At the end of the pulse period (12 or 24 h, as indicated in the text), the fatty acids were removed by washing the cells twice with phosphate-buffered saline containing 10 nmol/ml bovine serum albumin (essentially fatty acid-free) and twice with phosphate-buffered saline. One batch of cells was harvested at the end of the pulse (time 0 of the chase); the other batches were grown in a fresh medium containing 2% Ultroser G (but no additional fatty acids) and harvested at the indicated time of this chase period. Under the experimental conditions used here, fatty acids and MeSO had no adverse effect on cell viability.

Lipid Extraction and Analysis

Mass analysis of cellular lipids was performed by gas liquid chromatography. After adding tripentadecanoin (50 µg used as standard), cellular lipids were extracted according to the Folch procedure. After drying of the chloroformic phase, lipids were partitioned in the Dole's biphasic solvent system under the above indicated conditions. After evaporation of the heptane phase, neutral lipids were solubilized in 50 µl of hexane, and triacylglycerols were determined by gas liquid chromatography under the previously used conditions (24) (Carlo-Erba GC-8000; 6 M CP-Sil-5CB, 0.32-mm diameter capillary column; oven temperature programmed from 220 to 350 °C, 5 °C per min, flame ionization detector 370 °C, carrier gas N, 35 pK). Phospholipids (of the chloroformic phase of the Folch extract) were evaluated by their phosphorus content determined according to the method of Chen et al.(25) . Alternatively, gross triaglycerol mass was estimated by a method derived from Jefferson et al.(26) (briefly, after TLC separation of neutral lipids on Silica Gel G plates as above indicated (petroleum ether/diethyl ether/acetic acid, 80/20/1 (v/v/v) as developing system) and staining by dipping in 1 N sulfuric acid in methanol, followed by air drying for 15 min and heating at 180 °C for 15 min). Lipid component were quantified with a Biocom Image Station (Biocom-France) using a standard of tripentadecanoin treated under the same conditions on the same TLC plate (standard was linear between 5 and 50 µg).

In Vitro Enzymatic Assays and Preparation of [C]Decanoic-containing Triacylglycerols

Figure 6: Effect of E600 and PCMB on the in situ degradation of triacylglycerols endogenously biosynthesized from radiolabeled decanoic and oleic acids by fibroblasts from normal subjects. During the pulse period, cells were incubated at 37 °C for 12 h in RPMI 1640 medium supplemented with 2% Ultroser G and radiolabeled fatty acids, decanoic (A, C) or oleic (B, D) acids (10 dpm/ml and 30 nmol/ml non-labeled fatty acids). At the end of the 12-h pulse period (time 0 of the chase), total radioactivity levels, in cell batches used without (control) or with E600 and without (control) or with PCMB, were 0.67 ± 0.04, 0.69 ± 0.06, 0.70 ± 0.04, and 0.71 ± 0.05 with radiolabeled decanoic acid and 6.1 ± 0.4, 6.8 ± 0.8, 6.3 ± 0.6, and 6.2 ± 0.7 (as 10 dpm/mg cell protein) with radiolabeled oleic acid, respectively. After washing, cells were incubated in RPMI 1640 containing 2% Ultroser G for a 48-h chase period. Inhibitors, E600 (1 µmol/liter) (A, B) or PCMB (10 µmol/liter) (C, D), were added to the culture medium only during the chase period. Mean ± S.E. of three experiments.

Enzymatic Assays

Cell Microautoradiography

RESULTS

The Accumulation of Triacylglycerols in NLSD Fibroblasts Is Largely Dependent on the Presence of Lipids in the Culture Medium

Figure 1: Influence of lipids of the culture medium on the amounts of triacylglycerols in fibroblasts or lymphoblasts from a patient with NLSD(N1) and from normal subjects (no1 and no2). Cells were grown under the standard culture conditions either in the presence (FCS+, hatched bars) or absence (FCS-, black bars) of fetal calf serum for 15 days. Then, lipids were extracted, and the triacylglycerol mass was analyzed as indicated under ``Materials and Methods.'' Mean ± S.E. of three experiments. In insets are shown the thin layer chromatography of lipids extracted from fibroblasts (N1, NLSD; no1, normal) treated as indicated above, in the presence (+) or absence(-) of fetal calf serum.

Incorporation of Radiolabeled Fatty Acids with Various Acyl Chain Lengths into Cellular Lipids

Figure 2: Incorporation of radiolabeled short-, medium-, and long-chain fatty acids into cellular lipids of cultured fibroblasts from controls and patients with NLSD and Wolman disease at the end of the pulse period. Cells were incubated for 12 h in RPMI 1640 medium supplemented with 2% Ultroser G and fatty acids (radiolabeled fatty acids, 10 dpm/ml, were mixed with non-labeled fatty acid, 30 nmol/ml, i.e. 33,000 dpm/nmol). At the end of the pulse, fibroblasts were washed and harvested. Lipids were extracted by the procedure of Folch, and the radioactivity of the chloroformic phase was determined by liquid scintillation counting. The level of radiolabeled fatty acids incorporated into cellular lipids was calculated assuming that the radiolabeled and non-labeled fatty acids have the same metabolic fate (and on the basis of 33,000 dpm/nmol). Mean ± S.E. of four experiments.

Figure 3: Degradation of triacylglycerols and polar lipids (insets) endogenously biosynthesized from radiolabeled short-, medium-, and long-chain fatty acids incorporated in the culture medium of fibroblasts from normal subjects (filled squares and circles) and from patients with NLSD (empty squares and circles) and Wolman disease (triangles). Cells were incubated at 37 °C for 12 h (pulse period) in RPMI 1640 supplemented with 2% Ultroser G, and radiolabeled fatty acids (10 dpm/ml and 30 nmol/ml non-labeled fatty acid) are as described under ``Materials and Methods.'' At the end of the pulse period, cells were washed and incubated for an additional 24 or 48 h (chase period) in RPMI 1640 supplemented with 2% Ultroser G. At the indicated times, cells were washed and harvested, and the lipids were extracted and analyzed as described under ``Materials and Methods.'' Mean ± S.E. of three experiments. D and H, comparison of the levels of undegraded radiolabeled triacylglycerols in the various cell types at the end of the pulse (whole bars) and at the end of the 48-h chase period (black sections) with various fatty acids.

Figure 4: Microautoradiography of fibroblasts from a normal subject (A, B, E, F) and from NLSD (C, D, G, H) pulsed for 12 h with radiolabeled fatty acids (30 nmol/ml and 2.5 µCi/ml), [C]decanoic acid (A-D), or [C]oleic acid (E-H) and chased for an additional 48-h chase period in a fatty acid-poor medium, as described under ``Materials and Methods.'' Microautoradiographies were performed (under the procedure described under ``Materials and Methods''; exposure times were 4 and 1.5 days for [C]decanoic- and [C]oleic-labeled cells, respectively) after fixing the cells, either at the end of the pulse period (upper panel, A, C, E, G) or at the end of the chase period (lower panel, B, D, F, H). Magnification, 800.

It is noteworthy that, under the used experimental conditions of the pulse (12 or 24 h), elongation of C10 incorporated into cellular lipids was negligible. Reversely, we did not detect any appreciable amount of short derivatives of [H]oleic acid incorporated into cellular lipids. Similar data were observed with lipids extracted at the end of the chase (data not shown). These data allow to conclude that the chain lengths of the main part of fatty acids incorporated into cellular lipids remain unaltered during the time of the experiments reported here.

Study of the Degradation of Endogenously Biosynthesized Triacylglycerols Containing Fatty Acids with Various Chain Lengths ( Fig. 3and Fig. 4)

These conclusions were also supported by morphological (microautoradiographic) studies of the cellular radioactivity during pulse-chase experiments (Fig. 4). At the end of the pulse period, the level of radioactivity incorporated into the cells was higher with [C]oleic acid than with [C]decanoic acid, and the radioactivity was localized in the membranes and in the cytoplasmic compartment (Fig. 4, A, C, E, and G). These morphological features are in agreement with the metabolic studies (Fig. 3), which showed the incorporation of radiolabeled fatty acids into phospholipids and triacylglycerols. At the end of the chase, when cells were labeled with [C]oleic acid, the cytoplasmic radioactivity was lost in normal cells (Fig. 4F) but was still apparent in NLSD cells (Fig. 4H). This was quite consistent with the degradation of oleyl-containing triacylglycerols in normal but not in NLSD cells (Fig. 3G). In contrast, in cells labeled with [C]decanoic acid, the cytoplasmic radioactivity disappeared almost completely at the end of the chase in normal cells and in NLSD cells as well, the radioactivity being persistent only in cell membranes (Fig. 4, B and D). This was consistent with the normal degradation of [C]decanoic acid-containing triacylglycerols in NLSD cells (Fig. 3D).

As the accumulation of long-chain triacylglycerols in NLSD cells is due to a defect of the degradation pathway, it was suggested that, in the cytoplasmic compartment, short/medium-chain triacylglycerols could be degraded by an enzymatic system specific to short/medium-chain triacylglycerols and different from that hydrolyzing long-chain triacylglycerols (neutral lipase).

Mass Evaluation of Medium-chain and Long-chain Triacylglycerol Metabolism (Fig. 5)

Figure 5: Mass analysis of cellular triacylglycerols in pulse-chase experiments with a fixed concentration of decanoic (A) or oleic acid (B) in lymphoblasts from NLSD patient or normal subject. Cells were grown in a serum-free RPMI medium for 15 days, under the standard conditions of Fig. 1. Then, cells were pulsed with 30 nmol/ml decanoic acid for 24 h or oleic acid for 12 h. After washing, one batch was harvested for analysis (p), and another batch was grown in lipid-free medium (i.e. serum-free and fatty acid-free medium) for a 24-h chase period and washed and harvested for analysis (ch). Lipids were extracted and analyzed either by gas liquid chromatography or by thin layer chromatography as described under ``Materials and Methods.'' Hatched and black bars represent triacylglycerols with carbon number <45 and >48, respectively (note that no significant level of triacylglycerols with the carbon number <45 was detected in cells fed with oleic acid (panel B)). Mean ± S.E. of three experiments. In insets are shown the triacylglycerol TLC spots of the relative cells treated as indicated above.

Lymphoblasts grown in the presence of 30 nmol/ml C10 or C18:1 (for 24 and 12 h, respectively) showed that the levels of triacylglycerols, at the end of the pulse, were much lower in cells grown in the presence of C10 than in cells grown in the presence of C18:1 (Fig. 5). In normal cells, the levels of triacylglycerols were considerably reduced at the end of the 48-h chase (Fig. 5, A and B). In NLSD cells grown in the presence of oleic acid, the triacylglycerol level was almost unchanged (Fig. 5B), whereas it was reduced by about 50% in cells fed with C10 (Fig. 5A). Analysis of the triacylglycerol species in NLSD cells fed with C10 showed that triacylglycerols with a carbon number lower than 45 (triacylglycerols containing C10 or short/medium-chain fatty acid) were degraded during the chase, whereas triacylglycerols with a carbon number higher than 48 (long-chain triacylglycerols) were not degraded (Fig. 5A). In cells fed with C18:1, the major part of triacylglycerols have a carbon number higher than 48 and were not degraded in NLSD cells (Fig. 5B). These data confirm the results observed with radiolabeled fatty acids, supporting the idea that only long-chain containing triacylglycerols accumulate in NLSD cells, whereas medium-chain containing triacylglycerols do not accumulate in these cells.

Involvement of Two Separate Enzymatic Pathways in the Degradation of Short-chain and Long-chain Triacylglycerols ( Fig. 6and Fig. 7)

Figure 7: In vitro determination of activities of enzymes degrading radiolabeled decanoic acid- or oleic acid-containing triacylglycerols (A-D and E, respectively) in fibroblast homogenates (prepared in distilled water as described under ``Materials and Methods''). A, linearity of the enzyme activity versus time (standard assay conditions using 100 µg of protein of the homogenate per assay); B, linearity of the enzyme activity versus enzyme concentration (expressed as µg of homogenate protein/assay; incubation time, 2 h); C, effect of increasing concentrations of the substrate (100 µg of protein/assay; incubation time, 2 h); D and E, hydrolytic activity when varying pH from 3.5 to 9.0 using decanoic- or oleic-containing triacylglycerols as substrates (D and E, respectively). Mean ± S.E. of three experiments.

When intact normal cells were incubated in the presence of 1 µmol/liter E600, the in situ hydrolysis of short/medium-chain triacylglycerols was completely blocked (Fig. 6A), whereas that of long-chain triacylglycerols was not affected (Fig. 6B). In contrast, when intact normal cells were incubated in the presence of 10 µmol/liter PCMB, the in situ hydrolysis of long-chain triacylglycerols was severely impaired (Fig. 6C), whereas that of medium-chain triacylglycerols was not altered (Fig. 6D). The separate inhibition of the degradation pathways of short/medium- and long-chain triacylglycerols by these two inhibitors supports the hypothesis of two separate degradation pathways.

The activities of the two candidate enzymes were evaluated in homogenates of cells treated with the irreversible inhibitors under conditions of Fig. 6, using in vitro assays containing either [C]decanoic-containing triacylglycerols (prepared from cells loaded either with radiolabeled [C]decanoic acid or [H]triolein). The enzyme hydrolyzing C10-containing triacylglycerols was inhibited in cells treated by E600, whereas the enzyme hydrolyzing triolein was not inhibited in the same cells (Fig. 8, C and D). Reversely, in cells treated with PCMB, the enzyme hydrolyzing triolein was inhibited, whereas the enzyme hydrolyzing C10-containing triacylglycerols retained its activity (Fig. 8, C and D).

Figure 8: Comparison of inhibition of enzymes degrading radiolabeled decanoic acid- or oleic acid-containing triacylglycerols (A, C and B, D, respectively) by the irreversible inhibitors E600 (A, B) or PCMB (C, D) in vitro or ex situ. The enzyme activities were determined in vitro under the standard assay conditions, using radiolabeled decanoic acid- or oleic acid-containing triacylglycerols as substrate and fibroblast homogenates as enzyme sources, in the absence(-) or presence (+) of inhibitors used either in vitro (inhibitors added in the test tube) or ex situ (determination in vitro of the in situ inhibition: in this case, the intact living cells were incubated for 12 h with 1 µmol/liter E600 or 10 µmol/liter PCMB; then cells were harvested and homogenized, and the enzyme activity was determined under the standard conditions in the absence of any additional inhibitor). Mean ± S.E. of three experiments.

These results support the hypothesis that cytoplasmic C10-containing triacylglycerols are degraded in situ by an E600-sensitive short-chain lipase (not deficient in NLSD cells), which is clearly discriminated from the neutral lipase activity (specific to long-chain triacylglycerols) involved in the liberation of long-chain fatty acids of cytoplasmic triacylglycerols and deficient in NLSD cells.

DISCUSSION

The data previously reported (8, 9, 10, 31, 32) and those reported here clearly show that the cytoplasmic triacylglycerol accumulation in cultured fibroblasts is largely dependent on the extracellular lipids, since it is supplied by (at least) two separate pathways, the first one being the intracellular pathway of triacylglycerols endogenously biosynthesized from the cytoplasmic pool of fatty acids (8, 9, 10) and the second one (probably minor) resulting from the cellular uptake of triacylglycerols contained in high density lipoproteins(13) . Both sources of triacylglycerols have been shown to participate to the storage of cytoplasmic triacylglycerols in NLSD(8, 9, 10, 13) .

In the experiments reported here, the difference between the rates of incorporation of fatty acids with various acyl chain length into cellular lipids (under the used conditions, long-chain fatty acids were incorporated around 10 times faster than short- or medium-chain fatty acids) cannot be attributed to any cytotoxic artefactual effect (as assessed by the viability of 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide or trypan blue tests). The selectivity of incorporation of long-chain natural fatty acids into cellular lipids is consistent with the results observed with fluorescent fatty acid analogs (15, 33, 34) and with natural fatty acids(35) . As the ratio of triacylglycerols/polar lipids is nearly constant whatever the acyl chain length, it is suggested that the limiting step of short-chain fatty acid incorporation is probably an early metabolic step, such as transmembrane transport or biosynthetic pathway (for instance, acyl-CoA synthases are known to be acyl chain length-dependent) (36) .

Natural short-chain fatty acids were really incorporated into triacylglycerols, in contrast to short-chain fluorescent fatty acids (pyrene-butanoic acid), which were incorporated into phospholipids but not in triacylglycerols(15) . Therefore, the mechanism of the lack of accumulation of short/medium-chain triacylglycerols in NLSD cells is different with fluorescent fatty acids (lack of biosynthesis) and with natural fatty acids (lack of degradation block).

On the basis of genetic and inhibitor-induced metabolic blocks, it was suggested that cytoplasmic triacylglycerols are degraded through two separate catabolic pathways, one being specific to long-chain triacylglycerols (long-chain specific lipase activity) and the other one specific to short-chain triacylglycerols (short-chain specific lipase or carboxylesterase activity).

The genetic defect of the in situ triacylglycerol degradation in NLSD cells is specific to triacylglycerols containing dodecanoic and longer chain fatty acids, thus suggesting an in situ defect of the long-chain lipase activity. As the activity of the long-chain neutral lipase is apparently not deficient in vitro(10, 15) , it may be speculated that the mutation affects either a site involved in the lipase activity in situ (for instance, site for routing or enzyme activation) or a co-factor necessary to the lipase activity in situ by analogy with the co-lipase for the pancreatic lipase (37) or with the activator proteins (saposins) for several lysosomal enzymes(38, 39) . The normal degradation of short/medium-chain triacylglycerols (up to 10 carbons) in NLSD cells suggests that these lipids are degraded through a catabolic pathway different from and unable to compensate the in situ deficient activity of the long-chain lipase.

The hypothesis of the existence of two separate hydrolytic pathways is also supported by experiments with irreversible inhibitors specific to each degradation pathway and able to inhibit the enzyme activities in situ and in vitro as well. E600 inhibited concomitantly the degradation of short/medium-chain triacylglycerols in situ and the short-chain lipase activity in vitro but not the long-chain lipase in vitro activity nor the in situ degradation of long-chain triacylglycerols. Reversely, the sulfhydryl reagent PCMB inhibited the in situ degradation of long-chain triacylglycerols and the long-chain lipase activity in vitro, but not the in situ degradation of short/medium-chain triacylglycerols and the short/medium-chain lipase activity. Moreover, the inhibition of the enzymes (activities determined in vitro by using their respective substrates) persisting after lysis of cells treated with irreversible inhibitors, E600 and PCMB (this study), and the in vitro studies of enzymatic properties previously reported (1, 40, 41, 42) are consistent with the idea that the short-chain lipase is different from the long-chain lipase. The enzymatic properties (specificity to long-chain triacylglycerols, heat stability, susceptibility to PCMB but not to E600) of the neutral long-chain lipase (1, 5, 18, 42) are similar to those of the microsomal neutral lipase(43, 44, 45) , which has not been cloned to date, to our knowledge, and is different from the hormone-sensitive lipase (no activation of triacylglycerol degradation by dibutyryl-cAMP) (data not shown) and other known lipases by its enzymatic properties in vitro(1, 5) . The neutral short/medium-chain lipases exhibit some enzymatic properties (specificity to various short-chain lipophilic esters, heat lability, susceptibility to organophosphorous compound E600, but relative resistance to PCMB) similar to those of carboxylesterases(1, 40, 41, 42) , some of them having been cloned in liver or other tissues (45, 46, 47, 48) . As the enzymes are not identified at the molecular level, the alternative hypothesis that there is one lipase with differential substrate specificity cannot be excluded.

Finally, from the data observed in intact cells, i.e. degradation at a normal rate of short-chain triacylglycerols in NLSD (in contrast to the accumulation of long-chain triacylglycerols), it is suggested to use diets enriched with short/medium-chain lipids (and poor in long-chain lipids) to tentatively slow down the long-chain triacylglycerol accumulation in NLSD patients.

FOOTNOTES

*

This study was supported by grants from Association Française contre les Myopathies, INSERM (CJF 9206), Ministère de l'Enseignement Supérieur et de la recherche (JE DRED 174), and Conseil régional Midi-Pyrénées(9308181). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked ``advertisement'' in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

§

Recipient of a fellowship from Association Française contre les Myopathies.

¶

To whom correspondence should be addressed: Laboratoire de Biochimie, CHU Rangueil 1, Avenue J. Poulhès, 31054 Toulouse Cedex, France. Tel.: 33-61-32-27-05 or 33-61-32-28-08; Fax: 33-61-32-29-53.

()

The abbreviations used are: NLSD, neutral lipid storage disease; E600, diethylparanitrophenylphosphate; PCMB, parachloromercuribenzoate.

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