Individual Phospholipid Classes Research Articles

Monensin stimulates glycerolipid incorporation into rod outer segment membranes.

Monensin is an ionophore which disrupts the structure of the Golgi apparatus and inhibits vesicular transport in eukaryotic cells. In this study, we examined the effects of monensin on the incorporation of newly synthesized glycerolipids into retinal rod outer segment (ROS) membranes. Frog retinas were incubated in the presence or absence of monensin (50 nM) with either [1,2,3-3H]glycerol or [9,10-3H]palmitic acid as radiolabeled substrate. Total lipids were extracted from retinas and ROS membranes and resolved into individual phospholipid classes and neutral lipids by thin-layer chromatography. In the presence of monensin, the specific activity of ROS phospholipids was increased about 2-fold with [3H]glycerol and nearly 3-fold with [3H]palmitate as substrates relative to controls. In contrast, the specific activity of total retinal lipids, the relative incorporation of label into ROS and retinal phospholipids, and the total lipid phosphorous content of ROS membranes and retinas were not significantly different from control values. These data suggest that the enhanced labeling of ROS phospholipids in the presence of monensin was due to altered intracellular routing of lipids rather than increased glycerolipid synthesis. Under the same conditions, total retinal protein synthesis was about 90% of control, but light microscopic autoradiography indicated that newly synthesized proteins were not transported to the ROS for assembly into disc membranes. Thus, newly synthesized glycerolipids can be delivered to the ROS by a mechanism which is independent of protein transport to that cellular compartment.

Amniotic membrane production of prostaglandin F2 alpha is reduced in dysfunctional human labor: results of in vivo and in vitro studies.

Mobilization of arachidonic acid from glycerophospholipids and prostaglandin (PG) release from fetal membranes were studied in women with dysfunctional labor in the absence of cephalopelvic disproportion or fetal malposition. Using superfusion of intact amnion and chorion, we found a slight decrease in PGE and a more significant decrease in PGF release by the amniotic side of the fetal membrane obtained from women with dysfunctional labor compared to that in women with normal labor (PGE: normal labor, 2992 pg/cm2.h; dysfunctional labor, 1846 pg/cm2.h; P less than 0.05; PGF: normal labor, 662 pg/cm2.h; dysfunctional labor, 204 pg/cm2.h; P less than 0.02). Release of both prostanoids was significantly greater from the amniotic side in tissues obtained after labor compared to that in prelabor tissue. Analysis of arachidonic acid (by gas liquid chromatography) and phospholipid content (by two-dimensional thin layer chromatography) confirmed metabolic disposal of arachidonic acid from the amnion after the onset of labor. However, no difference in either phospholipid or phospholipase A2-releasable arachidonic acid of individual phospholipid classes was found in amnion tissue from women with normal and dysfunctional labor, suggesting similar activities of phospholipase A2 in these two groups. The finding of decreased free and phospholipase A2-releasable arachidonic acid of the total lipid extract of the amnion of women with dysfunctional labor could suggest further metabolic exhaustion of the substrate or failure of liberation of this fatty acid from glycerophospholipids by enzymes other than phospholipase A2, such as phospholipase C or diacyl and monoacylglycerolipases.

Properties of membrane phospholipids and their fatty acyl compositions of secretory granules from rat parotid gland

A secretory granular fraction isolated from rat parotid glands was remarkably different from a microsomal fraction in its phospholipid composition. It had higher levels of lysophospholipids (8%) and phosphatidylethanolamine (31%), while there were lower levels of phosphatidylcholine (40%) and phosphatidylserine (2.1%) than the microsomal fraction. However, fatty acid compositions of individual phospholipid classes from the two subfractions were found to be nearly similar to each other. ESR analysis demonstrated that extracted phospholipids from the secretory granular fraction were more fluid than those from microsomes. The relevance of these observations to physiological function of secretory granules is discussed.

Gamma-ray-induced biochemical changes in the outer mitochondrial membrane from kidney bean hypocotyls

Mitochondrial outer membranes were isolated from kidney bean hypocotyl segments exposed to 5000 Gy gamma radiation. The purified outer membrane fraction was found to be free from microsomes and mitoplast by showing the absence of their marker enzymes. The outer membrane fraction, constituting a small percentage of the total mitochondrial protein, was less after exposure to radiation. The marker enzyme activity, i.e. antimycin A-insensitive NADH-cyt C reductase, was also reduced markedly. A polyacrylamide gel electrophoretic profile of the membrane proteins showed a prominent but diffuse band of 29 kd molecular weight in irradiated material; it was clearly resolved in controls. A marked reduction in content of individual classes of phospholipids, particularly phosphatidyl choline, with a simultaneous increase in phosphatidic acid was observed. An increase in the cholesterol : phospholipid and a decrease in saturated : unsaturated fatty acid ratios suggested an increase in the fluidity of the membrane in the irradiated tissue.

Quantitative contributions of cholesterol and the individual classes of phospholipids and their degree of fatty acyl (un)saturation to membrane fluidity measured by fluorescence polarization.

Steady-state fluorescence polarization (P) measurements, using the probe 1,6-diphenyl-1,3,5-hexatriene, in a large variety of well-defined liposomes at 25 degrees C allowed a quantitative description of the contributions of cholesterol, sphingomyelin, and (un)saturation of fatty acyl groups in the various phospholipids to the structural order (or the mutual affinity) of membrane lipids. The P values for liposomes prepared from lipid extracts of natural (purified) membranes of various origins could be more or less predicted (calculated) from the relative contributions of the individual lipid components. In all cases, the polarization varied with the cholesterol/phospholipid molar ratio (C/PL) according to the equation P = Pplat -(Pplat -Pzero) exp(-alpha C/PL), in which Pzero refers to the polarization without cholesterol and Pplat is a maximal plateau value, reached at a high C/PL (greater than 1). The "cholesterol-ordering coefficient" alpha of the phospholipids was found to increase with the fraction of sphingomyelin or dipalmitoylphosphatidylcholine molecules, indicating that the susceptibility of phospholipids to be ordered by cholesterol is increased by these compounds. Pzero increases curvilinearly with the fraction of either of these molecules. Pplat increases linearly with the fraction of saturated acyl chains for most phospholipids. Highly unsaturated fatty acyl chains (e.g., 20:4 and 22:6) strongly depress Pplat but not Pzero. The results suggest that such phospholipids are unlikely to associate with cholesterol and may thus create extremely fluid membrane domains. The disproportionation of cholesterol in the cell can be understood by the differing composition of the phospholipids in plasma membranes and endomembranes and their ordering susceptibility (affinity) toward cholesterol.

31P-NMR investigation of magnetically oriented rod outer segments. Spectral analysis and identification of individual phospholipids.

A 31P-NMR study of magnetically oriented bovine rod outer segments is presented. We demonstrate that carefully isolated bovine rod outer segments retain the capacity to orient in a magnetic field. Maximal orientation (85-90%) is achieved at field strengths over 4.7 T in the NMR spectrometer. The lineshape of the 'oriented spectra' is totally different from the 'bilayer lineshape' of randomly oriented photoreceptor membranes. The oriented spectra consist of two phospholipid peaks, a major low-field peak (75-80% of the total intensity) near 30 ppm, and a minor high-field peak near - 14 ppm as well as two sharp metabolite peaks around 0 ppm. The phospholipid peaks are a composite of three narrower partially resolved resonances assigned to the individual phospholipid classes phosphatidylserine, phosphatidylcholine and phosphatidylethanolamine. Based on the morphology and magnetic anisotropy of the rod outer segment, the major phospholipid peak is attributed to the flat part of the disk membranes while the phospholipids of the plasma membrane are thought to contribute only to the minor peak. Disk rim phospholipids and non-oriented material contribute to the minor peak and, in addition, contribute some intensity to the middle part of the spectrum. The phospholipid class composition of the major peak is estimated by spectral simulation and is consistent with the phospholipid class composition of rod outer segment membranes. Hence, 31P analysis of oriented rod outer segments resolves the main phospholipids in at least two different membrane pools in the rod outer segment and allows the differential investigation of these pools. Most of the mobile phosphate metabolite intensity resides in the Pi peak at 3.5 ppm. A slight shift in the Pi resonance position indicates a 0.2 pH unit acidification upon illumination of rhodopsin. The absence of detectable nucleotide resonances, when compared with chemical analysis, indicates that the majority of the nucleotide population present is rather immobile and probably bound to the membranes.

Maintenance of epithelial surface membrane lipid polarity: a role for differing phospholipid translocation rates.

Large differences in lipid composition of apical and basolateral membranes from epithelial cells exist. To determine the responsible mechanism(s), rat renal cortical brush border and basolateral membrane phospholipids were labeled using 32P and either [3H]-glycerol or [2-3H] acetate for incorporation and degradation studies, respectively. Brush border and basolateral membrane fractions were isolated simultaneously from the same cortical homogenate. Different phospholipid classes were degraded at variable rates with phosphatidylcholine having the fastest decay rate. Decay rates for individual phospholipid classes were, however, similar in both brush border and basolateral membrane fractions. In phospholipid incorporation studies, again, large variations existed between individual phospholipid classes with phosphatidylcholine and phosphatidylinositol showing the most rapid rates of incorporation. Sphingomyelin and phosphatidylserine showed extremely slow incorporation rates and did not enter into the isotopic decay phase for 48 hr. In contrast to degradation studies, however, the same phospholipid class labeled the two surface membrane domains at highly variable rates. The difference in these rates, with the exception of phosphatidylinositol, were identical to the differences in phospholipid compositions between the two membranes. For example, phosphatidylcholine was incorporated into the basolateral membrane 2.5 X faster than into the brush border membrane and its relative composition was 2.5 X greater in the basolateral membrane. The opposite was true for sphingomyelin. These results indicate incorporation and not degradation rates of individual phospholipids play a major role in regulating the differing phospholipid composition of brush border and basolateral membranes.

Altered phospholipid metabolism in pressure-overload hypertrophied hearts.

The content and fatty acyl composition of phospholipids were examined in pressure-overload hypertrophied hearts. Cardiac hypertrophy was induced in rats by abdominal aortic constriction. Twenty-one days postconstriction the content of myocardial phosphatidylcholine (PC), sphingomyelin, and phosphatidylinositol (PI) was significantly elevated by 10, 10, and 20%, respectively. The essential fatty acid, linoleic acid, was markedly reduced in PC, phosphatidylethanolamine (PE), PI, and cardiolipin (CL) of hypertrophied hearts. The associated changes in fatty acyl composition were specific for the individual phospholipid class as evidenced by a significant elevation of palmitic acid in PC, docosahexaenoic acid in PE and oleic acid in CL. Alterations in fatty acyl composition of phospholipids were associated with no change in the composition of cardiac triglycerides, cardiac free fatty acids or serum lipids. The fatty acyl composition of phospholipids was also altered in pressure-overload hypertrophied hearts of cats, as evidenced by a reduction of linoleic acid and an elevation of arachidonic acid in total phospholipids. These findings demonstrate that changes in phospholipid metabolism occur in the pressure-overloaded mammalian heart. Such alterations may contribute to altered membrane function in the hypertrophied myocardium.

Thin-layer chromatography — flame ionization detection and the quantitation of marine neutral lipids and phospholipids

A method is described whereby a complete analysis of individual neutral lipid and phospholipid classes in marine animal total lipid can be achieved using an latroscan TLC-FID analyser. The method involves separate analyses of two samples of total lipid in solvents designed to separate neutral and polar lipid classes, together with calibration by a composite standard similar in composition to the sample under analysis. The method does not depend on the degree of unsaturation of the fatty acids present, is rapid and compares well in accuracy with conventional combined gravimetric, colouritnetric, and densitometric procedures.

Reversed-phase high-performance liquid chromatographic separation and mass detection of individual phospholipid classes

A reversed-phase high-performance liquid chromatographic method is described for the separation of individual classes of phospholipids into subtractions. The separation was achieved with isocratic elution using a Nucleosil-5 C 18 column and a mobile phase consisting of methanol, acetonitrile and water. Three commercial C 18 packing materials were evaluated before Nucleosil was chosen as the stationary phase. The compounds were detected with a combination of an UV detector and a light-scattering mass detector, which provided quantitative chromatograms reported for the first time. The mass detector also allowed location of the most relevant peaks of the UV chromatogram. Phosphatidylcholine and phosphatidylethanolamine species from egg, and phosphatidylcholine species from rat liver, were resolved into more than 20 peaks. The method can be applied to the separation of phospholipids from different biological sources.

A simplified procedure for estimation of lipid phosphorus in erythrocyte membranes

For the estimation of phospholipids and the other components of the erythrocyte membrane, methods are desirable that supply reproducible results, are simple and time-saving and, thus, practicable in a routine laboratory. Nowadays, nearly all procedures used for estimation of lipid phosphorus in the erythrocyte membrane require the application of extraction methods. The results of a variety of modifications of these methods are strongly affected by the composition of the solvent mixture as shown by Ways and Hanahan [l]. In addition to the extraction procedures of Folch et al [2], those of Rose and Oklander [3] have been applied in many investigations. However, the relatively considerable methodical deficiencies of all extraction procedures should not be ignored. To remove the disturbing non-covalently bound, phosphorus-containing compounds from the lipid extracts, a variety of wash procedures and specific after-treatments are necessary. Moreover, most of the methods known demand a quantitative preparation of erythrocyte ghosts before extraction. The quantitative manipulation of the ghosts during washing is difficult and high speed centrifugation (12000 X g) is necessary for the avoidance of losses. In order to overcome these difficulties, we have tested the polycationic dye Alcian blue for a quantitative preparation of erythrocyte ghosts. Some years ago this compound was used by us for haemagglutination experiments [4]. In the following, we will discuss the application of the erythrocytedye aggregates thus formed in a reproducible assay for the lipid phosphorus of the red cell membrane. This was compared with a method using an extraction procedure of a normal red cell suspension. In addition, some individual phospholipid classes were estimated by an extraction procedure of the Alcian blue ghost aggregates and also compared with our current method.

31P NMR as a tool for monitoring detergent solubilization of sarcoplasmic reticulum membranes

Sarcoplasmic reticulum vesicles were solubilized stepwise by the nonionic detergent octaethyleneglycol monododecyl ether; 31P NMR enabled the extent of phospholipid solubilization to be monitored by following the conversion of the broad resonance peak characterizing the phospholipids inserted in the bilayer to the narrow resonance signal characterizing phospolipids inserted into a mixed micelle. Up to 0.25 g detergent/g protein could be incorporated into the membrane without solubilization. Higher detergent concentrations of up to 1.5–2 g detergent/g protein led to gradual solubilization. Although the method allows us to monitor the extent of solubilization of individual phospholipid classes, there was no evidence of either preferential solubilization or retention of a specific class of phospholipids.

Changes in membrane lipid content after chronic ethanol administration with respect to fatty acyl compositions and phospholipid type

Changes in the relative proportions of the phospholipid fatty acids of erythrocyte membranes in mice after chronic ethanol treatment (4.5 g/kg, i.p. twice daily for one week) were shown to vary with the differing control profiles observed. It is suggested that certain changes in membrane lipid composition after ethanol administration may not be interpreted simply in terms of an adaptation to a disordering effect of the drug. The fatty acid changes were, in addition, distributed asymmetrically within the individual phospholipid classes. Depending on the control profile, the effects varied from being mainly in phosphatidylethanolamine (PE; 80%) and phosphatidylserine-inositol (PS + PI; 10%), phospholipids primarily located on the inner half of the membrane bilayer, to being more evenly distributed between PE and phosphatidylcholine (PC) and probably, therefore, between the two halves of the bilayer. Changes in the monounsaturated acid remained primarily with PE, suggesting a specific functional role for this species. The remaining results are discussed in the light of possible effects on cell morphology and their potentially similar consequences of increasing cell volume.

Effect of dietary cod-liver oil on the lipid composition of human erythrocyte membranes.

The effect of dietary cod-liver oil on factors which characterize membrane lipid fluidity was studied. To six volunteers a daily supplement of 15 ml of cod-liver oil, providing 3 g of omega 3 fatty acids, was given for 2 weeks. Changes induced by the supplement in the fatty acid patterns of the individual erythrocyte phospholipid classes did not occur at the same rate or in the same degree. A rapid incorporation of omega 3 fatty acids in plasma lipids and in erythrocyte phosphatidyl choline, at the expense of linoleic acid, was seen, resulting in increased total unsaturation. A slower and quantitatively smaller incorporation of omega 3 fatty acids in erythrocyte phosphatidyl ethanolamine and phosphatidyl serine was seen. No change in the fatty acid pattern of sphingomyelin was seen. Withdrawal of the supplement for 2 weeks did partly reverse the cod-liver oil induced changes in erythrocyte phosphatidyl choline, while the changes in erythrocyte phosphatidyl ethanolamine and phosphatidyl serine lasted. Neither a change in distribution of erythrocyte phospholipid classes, nor in the erythrocyte cholesterol/phospholipid ratio was found. The observed changes in lipid composition are indicative of an increased lipid fluidity.

Action of phospholipase C (Bacillus cereus) on isolated myelin sheath preparations

The action of phospholipase C (Bacillus cereus) on the phospholipids of myelin sheath preparations has been investigated. With freshly isolated bovine brain myelin about 40% of the total phospholipid could be hydrolyzed by this enzyme. With bovine spinal cord myelin the phospholipid seemed more resistant to attack whereas the opposite was the case with myelin from guinea-pig brain or rat brain. With fresh bovine brain myelin, phosphatidylcholine and the ethanolamine-containing phospholipids were the main targets for the enzyme with lesser extents of hydrolysis occurring with phosphatidylserine and sphingomyelin. The effect of exposing bovine brain myelin to structural perturbants prior to enzyme digestion indicated that trypsin pretreatment had no significant effect, whereas marked enhancement of the extent of phospholipid hydrolysis occurred following lyophilization + rehydration, or pretreatment of myelin with HCl, Triton TX-100/ammonium acetate or deoxycholate. The effect of myelin pretreatment on the degradation of the individual phospholipid classes was also studied.

Suppression of Arachidonic Acid in Lipids of Rat Tissues by Dietary Mixed Isomeric cis and trans Octadecenoates

The influence of dietary isomeric cis and trans octadecenoic fatty acids (ICTO) on the metabolism of polyunsaturated fatty acids in rat tissues was studied by feeding a defined diet rich in partially hydrogenated soybean oil. Experimental and control animals received equal and more than adequate amounts of linoleic and linolenic acids. The total phospholipid (PL) fatty acids of liver, heart, testis, brain and sciatic nerve, and the fatty acids of liver triacylglyceride, cholesteryl ester and individual PL classes were analyzed by capillary gas chromatography. The content of arachidonic acid in the total fatty acids of liver lipids of ICTO-fed rats was found to be lower than those from control rats by the following amounts (in percent): total PL, 35; phosphatidylcholine, 50; phosphatidylinositol, 35; phosphatidylserine 26; phosphatidylethanolamine, 12; cholesteryl ester, 55; and tryglyceride 75. PL 18:2ω6 and 20:3ω6 levels were elevated, suggesting inhibition of the desaturase-elongase enzymes involved in synthesis of arachidonic acid. Synthesis of 20:5ω3 and 20:3ω9 was accentuated by the ICTO diet, suggesting an ω6 series-specific inhibition. A nearly perfect negative correlation between cis 12–18:1 and arachidonic acid was found in liver PL.

Alterations in newborn and adult rat lung morphology and phospholipid levels after chlorcyclizine or chlorphentermine treatment

Daily, po administration of chlorcyclizine at doses of 10, 30, or 60 mg/kg for 7 days to adult or newborn rats did not significantly alter relative lung to body weight. Only in the case of newborns administered 60 mg/kg/day chlorcyclizine for 1 week was there an accumulation of hypertrophic macrophages in pulmonary alveoli accompanied by an increase in total phospholipid and phosphatidylcholine levels. In comparison, varying chlorcyclizine doses given po for 7 days failed to alter adult lung morphology and phospholipid levels. While prolongation of chlorcyclizine treatment (60 mg/kg/day) for 2 weeks failed to markedly change relative lung weight in adults and newborns, an equivalent chlorphentermine dose significantly elevated this weight in either group. In adults, chlorcyclizine treatment for 2 weeks produced an accumulation of alveolar hypertrophic macrophages; however, this reaction occurred after 1 week in newborns. The chlorcyclizine-induced foam cell development in either age group was associated with an increase in lung phosphatidylcholine and total phospholipid as well as a fall in glycogen levels. In newborns or adults administered chlorphentermine, the resultant accumulation of hypertrophic macrophages was accompanied by a rise in total phospholipid as well as a rise in all individual phospholipid classes extracted but without a marked change in glycogen content. In view of the differences in lung responsiveness between chlorphentermine and chlorcyclizine, our data suggest that time and dose play a role in the observed drug-induced pulmonary phospholipidosis.

Lipid composition of transverse tubular membanes from normal and dystrophic skeletal muscle

Vesiculated fractions of transverse tubular (TT) membranes were isolated from normal and genetically dystrophic breast muscle of the chicken. The lipid composition of the TT was compared to the lipids of highly purified sarcoplasmic reticulum (SR) membranes and enriched fractions of sarcolemma (SL) membranes. Normal TT membranes contained a significantly higher molar ratio of cholesterol to phospholipid phosphorous (0.86) when compared to both SR (0.17) and SL (0.38) membranes. The phospholipid phosphorous-to-protein ratio was highest for SL (1.55 μmol phosphorous/mg), intermediate for TT (1.09), and lowest for the SR (0.79) membranes. TT membranes contained lower amounts of phosphatidylcholine and higher amounts of sphingomyelin when compared to SR while the TT phospholipid distribution was not significantly different from that of the SL. These data indicate that our putative TT fraction displays a lipid composition distinctly different from that of SR and SL and confirms other biochemical and morphological data which indicate that they are of TT origin. All three membrane classes isolated from dystrophic muscle displayed significant alterations in the composition of various lipids. Cholesterol levels were elevated most notably in SL (2.4-fold) followed by the SR (1.3-fold) but not TT membranes. Dystrophic TT and SL but not SR displayed elevated levels of phospholipid phosphorous. Few differences in the distribution of the individual phospholipid classes were found among the dystrophic membranes except for a 2.2-fold increase in the sphingomyelin content of the SR. The observed lipid abnormalities may be the underlying cause of reported alterations in excitation-contraction coupling and suggest that avian dystrophy may result from a generalized membrane defect.

Turnover of axonally transported phospholipids in nerve endings of retinal ganglion cells.

We have investigated the metabolic turnover of axonally transported phospholipids in myelinated axons (optic tract) and nerve endings (superior colliculus) of retinal ganglion cells. One week following intraocular injection of [2-3H]glycerol, turnover rates for individual phospholipid classes in the retina (which contains a number of other cell types in addition to the ganglion cells) were all very similar to each other, with apparent half-lives of approximately 7 days. Apparent half-lives of labeled phospholipids in superior colliculus (presumably primarily in retinal ganglion cell nerve endings) were 10 days for both choline and inositol phosphoglycerides and 13 days for both serine and diacylethanolamine phosphoglycerides. Subcellular fractionation data obtained from superior colliculus at various times after injection suggested that apparent turnover rates determined for nerve ending phospholipids probably were not significantly affected by transfer of axonally transported 3H lipids into myelin. Apparent half-lives for phospholipids in optic tract were somewhat longer than in superior colliculus, ranging from 11 to 18 days. The slower turnover rates in optic tract may, in part, reflect the transfer of some axonal lipids to the more metabolically stable pool of lipids in the myelin ensheathing the retinal ganglion cell axons. In both optic tract and superior colliculus, apparent half-lives for axonally transported phospholipids labeled with [32P]phosphate were only slightly longer than for [2-3H]glycerol, while those for [14C]choline and [3H]acetate were markedly longer, indicating differing degrees of metabolic conservation or reutilization of these precursors relative to glycerol.

Isolation and characterization of the plasma membranes of cultured lymphoblasts from patients with cystic fibrosis and normal individuals

Plasma membranes were isolated from two cystic fibrosis lymphoblastoid cell lines and two age and sex-matched normal cell lines after controlled cell disruption. The preparations were enriched approx. 20-fold in plasma membrane markers and were essentially free of markers for other organelles except the Golgi-localized enzyme, galactosyltransferase. Sodium dodecyl sulphate polyacrylamide gel electrophoresis showed virtually identical polypeptide profiles after staining with Coomassie blue. Membranes from normal cells contained 0.49–0.67 μmol of total phospholipid/mg membrane protein and those from cystic fibrosis cells, 0.53–0.67 μmol. The cholesterol content was 0.35–0.41 μmol/mg protein for normal, and 0.43–0.49 μmol for cystic fibrosis cell membranes. The proportions of individual phospholipid classes and their fatty acid compositions as well as that of the total membrane lipid also did not differ significantly in the two cell types. The bulk lipid fluidity as reflected by the fluorescence polarization of β-parinaric acid and diphenylhexatriene was also not changed. The carbohydrate composition of cell surface glycopeptides released with papain was not consistently different with the normal and cystic fibrosis cells. The quantity of fucose in intact plasma membranes was also quantitated enzymatically and found to be very similar in both cell types.