Cuticular lipids of insects. VI. Cuticular lipids of the grasshoppers Melanoplus sanguinipes and Melanoplus packardii

The cuticular lipids of the grasshoppers Melanoplus sanguinipes and Melanoplus packardii contain 60 and 68% alkanes and 28 and 18% secondary alcohol wax esters, respectively, with lesser amounts of normal and sterol wax esters, triglycerides, alcohols, sterols, and free fatty acids. All the hydrocarbons are saturated, and four types of alkanes are present: n-alkanes, 3-methylalkanes, internally branched monomethylalkanes, and internally branched dimethylalkanes. The principal n-alkanes in both insects are C(29) and C(27), with a range from C(21) to C(33). Trace amounts of 3-methylalkanes of 28, 30, and 32 total carbons are present. The principal internally branched monomethylalkanes are C(32) and C(34), whereas the main dimethylalkane contains 35 carbons. The n-alkanes do not correspond in chain length to the secondary alcohols. The primary alcohols range from C(22) to C(32) in both insects, with C(24) and C(26) predominating. The fatty acids in the triglyceride and free fatty acid fractions range from C(12) to C(24) in M. sanguinipes and from C(12) to C(18) in M. packardii.     

Differential scanning calorimetry study of mixed-chain phosphatidylcholines with a common molecular weight identical with diheptadecanoylphosphatidylcholine

To examine the thermotropic phase behavior of various mixed-chain phosphatidylcholines in excess water and to compare it with the known behavior of identical-chain phosphatidylcholines, we have carried out high-resolution differential scanning calorimetric (DSC) studies on aqueous dispersions of 10 different mixed-chain phosphatidylcholines. These lipids, C(16):C(18)PC, C(18):C(16)PC, C(15):C(19)PC, C(19):C(15)PC, C(14):C(20)PC, C(20):C(14)PC, C(13):C(21)PC, C(21):C(13)PC, C(12):C(22)PC, and C(22):C(12)PC, have a common molecular weight which is the same as that of C(17):C(17)PC, an identical-chain phosphatidylcholine with a molecular weight of 762.2. When the values of any of the thermodynamic parameters (Tm, delta H, and delta S) of the mixed-chain phosphatidylcholines and C(17):C(17)PC are plotted against the normalized chain-length difference (delta C/CL), a linear function with negative slope is obtained provided that the value of delta C/CL is within the range of 0.09-0.4. The linear relationship suggests that these mixed-chain phospholipids are packed in the gel-state bilayer similar to the bilayer structure of C(17):C(17)PC at T less than Tm; however, the negative slope suggests that the conformational statistics of the hydrocarbon chain and the lateral lipid-lipid interactions of these phosphatidylcholines in the gel-state bilayer are perturbed proportionally by a progressive increase in the chain-length inequivalence between the two acyl chains within each lipid molecule. When the value of delta C/CL for mixed-chain phosphatidylcholines reaches the range of 0.44-0.55, the thermotropic phase behavior deviates markedly from that of less asymmetric phosphatidylcholines, suggesting that these highly asymmetric lipids are packed into mixed interdigitated bilayers at T less than Tm. The heating and cooling pathways of aqueous dispersions prepared from the 10 mixed-chain phospholipids are also discussed.     

Citrate sensing by the C4-dicarboxylate/citrate sensor kinase DcuS of Escherichia coli: binding site and conversion of DcuS to a C4-dicarboxylate- or citrate-specific sensor

The histidine protein kinase DcuS of Escherichia coli senses C(4)-dicarboxylates and citrate by a periplasmic domain. The closely related sensor kinase CitA binds citrate, but no C(4)-dicarboxylates, by a homologous periplasmic domain. CitA is known to bind the three carboxylate and the hydroxyl groups of citrate by sites C1, C2, C3, and H. DcuS requires the same sites for C(4)-dicarboxylate sensing, but only C2 and C3 are highly conserved. It is shown here that sensing of citrate by DcuS required the same sites. Binding of citrate to DcuS, therefore, was similar to binding of C(4)-dicarboxylates but different from that of citrate binding in CitA. DcuS could be converted to a C(4)-dicarboxylate-specific sensor (DcuS(DC)) by mutating residues of sites C1 and C3 or of some DcuS-subtype specific residues. Mutations around site C1 aimed at increasing the size and accessibility of the site converted DcuS to a citrate-specific sensor (DcuS(Cit)). DcuS(DC) and DcuS(Cit) had complementary effector specificities and responded either to C(4)-dicarboxylates or to citrate and mesaconate. The results imply that DcuS binds citrate (similar to the C(4)-dicarboxylates) via the C(4)-dicarboxylate part of the molecule. Sites C2 and C3 are essential for binding of two carboxylic groups of citrate or of C(4)-dicarboxylates; sites C1 and H are required for other essential purposes.     

Mixing behavior of identical molecular weight phosphatidylcholines with various chain-length differences in two-component lamellae.

It has recently been suggested that mixed-chain phosphatidylcholines with normalized chain length differences (deltaC/CL) in the range of 0.10-0.40 undergo spontaneous self-assembly in excess water at T less than Tm into the partially interdigitated bilayer and those with delta C/CL values in the range of 0.44-0.57 form, in excess water, mixed interdigitated bilayers at T less than Tm. The mixing behavior of binary mixtures of C(22):C(12)PC/C(17):C(17)PC, C(22):C(12)/C(15):C(19)PC, and C(15):C(19)PC/C(13):C(21)PC reported in this work is used to support this view. The values of delta C/CL for C(17):C(17)PC, C(15):C(19)PC, C(13):C(21)PC, and C(22):C(12)PC are 0.10, 0.15, 0.35, and 0.55, respectively. The binary mixture of C(15):C(19)PC/C(13):C(21)PC exhibits a lens-shaped phase diagram, indicating that these two identical molecular weight (MW) lipids with delta C/CL values less than 0.4 are completely miscible over the entire compositional range in both gel and liquid-crystalline phases. In contrast, the phase diagrams of C(22):C(12)PC/C(17):C(17)PC and C(22):C(12)PC/C(15):C(19)PC are eutectic, indicating immiscibility of the component lipids over a wide compositional range in the gel phase. This immiscibility of identical MW lipids in the bilayer plane can be attributed to the different packing properties of the component lipids in the bilayer at T less than Tm.     

The taxonomic distribution of C4 photosynthesis in Amaranthaceae sensu stricto

C(4) photosynthesis evolved multiple times in the Amaranthaceae s.s., but the C(4) evolutionary lineages are unclear because the photosynthetic pathway is unknown for most species of the family. To clarify the distribution of C(4) photosynthesis in the Amaranthaceae, we determined carbon isotope ratios of 607 species and mapped these onto a phylogeny determined from matK/trnK sequences. Approximately 28% of the Amaranthaceae species use the C(4) pathway. C(4) species occur in 10 genera-Aerva, Amaranthus, Blutaparon, Alternanthera, Froelichia, Lithophila, Guilleminea, Gomphrena, Gossypianthus, and Tidestromia. Aerva, Alternanthera, and Gomphrena contain both C(3) and C(4) species. In Aerva, 25% of the sampled species are C(4). In Alternanthera, 19.5% are C(4), while 89% of the Gomphrena species are C(4). Integration of isotope and matK/trnK data indicated C(4) photosynthesis evolved five times in the Amaranthaceae, specifically in Aerva, Alternanthera, Amaranthus, Tidestromia, and a lineage containing Froelichia, Blutaparon, Guilleminea, Gomphrena pro parte, and Lithophila. Aerva and Gomphrena are both polyphyletic with C(3) and C(4) species belonging to distinct clades. Alternanthera appears to be monophyletic with C(4) photosynthesis originating in a terminal sublineage of procumbent herbs. Alpine C(4) species were also identified in Alternanthera, Amaranthus, and Gomphrena, including one species (Gomphrena meyeniana) from 4600 m a.s.l.     

The role of proteins in C(3) plants prior to their recruitment into the C(4) pathway

Our most productive crops and native vegetation use a modified version of photosynthesis known as the C(4) pathway. Leaves of C(4) crops have increased nitrogen and water use efficiencies compared with C(3) species. Although the modifications to leaves of C(4) plants are complex, their faster growth led to the proposal that C(4) photosynthesis should be installed in C(3) crops in order to increase yield potential. Typically, a limited set of proteins become restricted to mesophyll or bundle sheath cells, and this allows CO(2) to be concentrated around the primary carboxylase RuBisCO. The role that these proteins play in C(3) species prior to their recruitment into the C(4) pathway is addressed here. Understanding the role of these proteins in C(3) plants is likely to be of use in predicting how the metabolism of a C(3) leaf will alter as components of the C(4) pathway are introduced as part of efforts to install characteristics of C(4) photosynthesis in leaves of C(3) crops.     

Normal cellular prion protein is preferentially expressed on subpopulations of murine hemopoietic cells

We studied the expression of normal cellular prion protein (PrP(C)) in mouse lymphoid tissues with newly developed mAbs to PrP(C). Most of the mature T and B cells in the peripheral lymphoid organs do not express PrP(C). In contrast, most thymocytes are PrP(C+). In the bone marrow, erythroid cells and maturing granulocytes are PrP(C+). Approximately 50% of the cells in the region of small lymphocytes and progenitor cells also express PrP(C). Most of these PrP(C+) cells are CD43(+), but B220(-), surface IgM(-) (sIgM(-)), and IL-7R(-), a phenotype that belongs to cells not yet committed to the B cell lineage. Another small group of the PrP(C+) cell are B220(+), and some of these are also sIgM(+). The majority of the B220(+) cells, however, are PrP(C-). Therefore, PrP(C) is preferentially expressed in early bone marrow progenitor cells and subsets of maturing B cells. Supporting this interpretation is our observation that stimulation of bone marrow cells in vitro with PMA results in a decrease in the number of PrP(C+)B220(-) cells with a corresponding increase of sIgM(+)B220(high) mature B cells. This result suggests that the PrP(C+)B220(-) cells are potential progenitors. Furthermore, in the bone marrow of Rag-1(-/-) mice, there are an increased number of PrP(C+)B220(-) cells, and most of the developmentally arrested pro-B cells in these mice are PrP(C+). Collectively, these results suggest that PrP(C) is expressed preferentially in immature T cells in the thymus and early progenitor cells in the bone marrow, and the expression of PrP(C) is regulated during hemopoietic differentiation.     

Synthesis of highly 13C enriched carotenoids: access to carotenoids enriched with 13C at any position and combination of positions

Carotenoids and their metabolites are essential factors for the maintenance of important life processes such as photosynthesis. Animals cannot synthesize carotenoids de novo, they must obtain them via their food. In order to make intensive animal husbandry possible and maintain human and animal health synthetic nature identical carotenoids are presently commercially available at the multi-tonnes scale per year. Synthetically accessible (13)C enriched carotenoids are essential to apply isotope sensitive techniques to obtain information at the atomic level without perturbation about the role of carotenoids in photosynthesis, nutrition, vision, animal development, etc. Simple highly (13)C enriched C(1), C(2) and C(3) building blocks are commercially available via 99% (13)CO. The synthetic routes for the preparation of the (13)C enriched building blocks starting from the commercially available systems are discussed first. Then, how these building blocks are used for the synthesis of the various (13)C enriched carotenoids and apocarotenoids are reviewed next. The synthetic Schemes that resulted in (13)C enriched β-carotene, spheroidene, β-cryptoxanthin, canthaxanthin, astaxanthin, (3R,3'R)-zeaxanthin and (3R,3'R,6'R)-lutein are described. The Schemes that are reviewed can also be used to synthetically access any carotenoid and apocarotenoid in any (13)C isotopically enriched form up to the unitarily enriched form.     

Characterization of uniaxially aligned chitin film by 2D FT-IR spectroscopy

Two-dimensional FT-IR spectroscopy (2D FT-IR) was applied to the investigations of crystalline chitin structure. From this study, new information about spectral bands which are not observed in conventional 1D FT-IR was obtained. In 2D spectra, three specific bands were differentiated at 3482, 3421, and 3380 cm(-1) in the OH region. They could be assigned as C(6)OH groups which are hydrogen-bonded to the next C(6)OH; C(3)OH groups hydrogen-bonded to O(5); and C(6)OH groups bifurcated hydrogen-bonded to C(6)OH as well as C=O, respectively. Two pairs of bands appeared in the amide region, indicating the two types of hydrogen-bonded states of C=O groups. This is in good agreement with the results in the OH region; half of the C(6)OH groups are hydrogen-bonded to C=O as well as the next C(6)OH. The results accurately confirmed the Blackwell model which was established by an X-ray diffraction study. The temperature-dependency of hydrogen-bonds was also revealed by 2D FT-IR. Interchain hydrogen-bonds [C(6)OH...O(6)] first respond to a temperature followed by intrachain [C(6)OH...O=C] and [C(3)OH...O(5)] with increasing temperature. Interchain hydrogen-bonds [NH...O=C] are relatively stable in the temperature range of 40-180 degrees C.     

Cellular prion proteins in human platelets show a phenotype different to those in brain tissues

Prion diseases are characterized by high accumulation of infectious prion proteins (PrP(Sc)) in brains. PrP(Sc) are propagated by the conversion of host-encoded cellular prion proteins (PrP(C)) which are essential for developing the disease but are heterogeneously expressed in brains. The disease can be transmitted to humans and animals through blood and blood products, however, little attention has been given to molecular characterization of PrP(C) in blood cells. In this presented study, we characterized phenotypically PrP(C) of platelets (plt) and characterized the proteins regarding their glycobanding profiles by quantitative immunoblotting using a panel of monoclonal antibodies. The glycosylation patterns of plt and brain PrP(C) were compared using the ratios of di-, mono-, and non-glycosylated prions. The detergent solubility of plt and brain PrP(C) was also analyzed. The distinct banding patterns and detergent solubility of plt PrP(C) differed clearly from the glycosylation profiles and solubility characteristics of brain PrP(C). Plt PrP(C) exhibited single or only few prion protein types, whereas brain PrP(C) showed more extensive banding patterns and lower detergent solubility. Plt PrP(C) are post-translational modified differently from PrP(C) in brain. These findings suggest other or less physiological functions of plt PrP(C) than in brain.     

Species of the genus Crotonia (Acari: Cryptostigmata) from New Zealand

Five new species of Crotonia from New Zealand ( C. cervicorna, C. cupulata, C. longibulbula, C. tuberculata and C. reticulata ) are described as new, and two species ( C. cophinana (Michael 1908) and C. caudatis (Hammer 1966)) are redescribed. Five species groups of the genus are characterized and a key to the adequately described species of the world is presented.     

Differences in substrate specificity of C(5)-substituted or C(5)-unsubstituted pyrimidine nucleotides by DNA polymerases from thermophilic bacteria, archaea, and phages

The pyrimidine bases of RNA are uracil (U) and cytosine (C), while thymine (T) and C are used for DNA. The C(5) position of C and U is unsubstituted, whereas the C(5) of T is substituted with a Me group. Miller et al. hypothesized that various C(5)-substituted uracil derivatives were formed during chemical evolution, and that C(5)-substituted U derivatives may have played important roles in the transition from an 'RNA world' to a 'DNA-RNA-protein world'. Hyperthermophilic bacteria and archaea are considered to be primitive organisms that are evolutionarily close to the universal ancestor of all life on earth. Thus, we examined the substrate specificity of several C(5)-substituted or C(5)-unsubstituted dUTP and dCTP analogs for several DNA polymerases from hyperthermophilic bacteria, hyperthermophilic archaea, and viruses during PCR or primer extension reaction. The substrate specificity of the C(5)-substituted or C(5)-unsubstituted pyrimidine nucleotides varied greatly depending on the type of DNA polymerase. The significance of this difference in substrate specificity in terms of the origin and evolution of the DNA replication system is discussed briefly.     

Notes on the genus Clematis (Ranunculaceae) (Ⅱ)

(1) The systematic positions of Clematis potaninii Maxim., C . heynei Rau, C. trichotoma Nakai, C. apiculata Hook. f. & Thoms, C. theobromina Dunn, C. sigensis Engler,C. hedysarifolia DC., and C. dissecta Baker, and the specific status of C. trifida Hook, C.pimpinellifolia Hook., C. oligophylla Hook., and Clematopsis lineariloba Hutch. are discussed; (2) New classifications for Clematis parviloba Gardn. & Champ., C. puberula Hook. f. & Thoms., and sect. Naraveliopsis Hand.-Mazz. are provided; (3) Clematis subsect. Potaninianae M. Johnson, C. heynei M. Johnson, C. petelotii Gagnep. and some other names are reduced to synonymy; (4) Two subsections, 4 series, 4 species, and 4 varieties are described as new; (5)Four new ranks and 4 new combinations are made.     

A Study on Chemical Components of Essential Oils from Citrus bergamia and Its Close Relatives and Its Taxonomy

Citrus bergamia Risso. is a rare perfumery plant. Taxonomists have different views on the taxonomy of C. bergamia. Chemical components of leaf and peel essential oils from C. bergamia, and its close relatives, C. limon, C. aurantifolia and three varieties of C. aurantium, were analyzed by GC and GC-MS. The analytical result shows that the chemical compositions of the leaf essential oils from C. bergamia are basically the same as those from three varieties of C. aurantium. Their main components are linalool (29.19-39.75% )and linalyl acetate (24.73-30.24% )etc., and contents of other components are also similar. But their peel essential oils are different. The peel essential oils from C. bergamia contain less limonene (29.94%) than those from C. aurantium (92.55-94.31% ) and less beta-pinene (3.00%) and y-terpinene(3.48% )than those from C. limon or C. aurantifolia (respectiyely 9.16% and 10.42% ) . The peel essential oils from C. bergamia contain not only as much linalool (22.20%) and linalyl acetate (32.66%)as those in the leaf essential oils from C. aurantium, but also as much limonene(29.94% )as that in the peel essential oils from C. limon or C. aurantifolia . The contents of limonene are close to those of the essential oils from C. aurantifolia. This result shows that C. bergamia may be a natural hybrid between C.aurantium and C. aurantifolia, as proposed by Sinclair W. B.     

Cuticular hydrocarbons and wax esters of the ectoparasitoid Habrobracon hebetor: Ontogenetic,reproductive, and nutritional effects

Hydrocarbon and wax ester components of cuticular lipids of the braconid parasitoid Habrobracon hebetor Say reared at 25 degrees C on larvae of a pyralid moth have been identified by GC-MS and analyzed with respect to adult age, mating status, and diet. The hydrocarbons range in carbon number from C(21) to C(45) and consist of a homologous series of n-alkanes, 11-, 13-, and 15-methyl alkanes, 13,17-dimethyl alkanes, and Z-5, Z-7, and Z-9-alkenes. The wax esters found in the cuticular lipid fraction are a series of homologous compounds with the acid portion being short chain, unbranched, even carbon number acids from C(8) to C(20) (predominately C(8) to C(16)). The alcohol portions of the esters are secondary alcohols with carbon number from C(22) to C(25) (predominately C(23) and C(25)) with the hydroxyl function located at C(6), C(7), C(8), and C(9). Gender, age, and nutritional states were significant factors for variation in several of the individual esters, but mating status did not affect wax ester composition. Ontogenetic examinations indicated that prepupal, and early pupal cuticular lipids contain only hydrocarbons. Low levels of wax esters are detectable in late stage pupae, and somewhat greater quantities of wax esters are present on newly eclosed adults. When pharate adults emerge from the cocoon, however, their cuticular lipids consist of approximately equal amounts of hydrocarbons and wax esters, and 6d post emergence from the cocoon, wax esters are the predominant lipid component.     

Current state of carotenoid biosynthesis in chloroplasts of eucaryotes

The author discusses the current state of biochemical and genetic aspects of carotenoid biosynthesis in chloroplasts of algae and higher plants. Two ways of biosynthesis of key C5-isoperene units have been considered: 1) from acetate (C2) via mevalonic acid (C6) and its enzymatic conversions up to isopenthenyl diphosphate (C5) and 2) from glucose (C6) to formation of glyceraldehyde-3-phosphate (C3), to piruvate and their condensation via intermediate products up to isopenthenyl diphosphate (C5). Further biosynthesis of carotenoids from isopenthenyl diphosphate (C5) and dimethylallyl diphosphate (C5) in every organism is effected by the common scheme with further conservation of them up to geranyl diphosphate (C10), farnesyl diphosphate (C15), geranylgeranyl diphosphate (C20) and synthesis of phytoene (C40). All stages of phytoene desaturation up to formation of acyclic compounds are discussed. It is shown how in the process of subsequent oxidation and formation of hydroxy-, epoxy- and oxo-groups cyclic xanthophylls in chloroplasts of plants and algae are formed. Genetic control over biosynthesis of carotenoids is discussed.     

Analogous antigenic alterations elicited in C3 by physiologic binding and by denaturation in the presence of sodium dodecylsulfate

The expression of three antigenic subsets of C3--the C3(S), the C3(N), and the C3(D) antigens--by soluble and target-bound forms of C3 was studied. The C3(S) subset is stable and is expressed by native as well as denatured C3 (exposure to sodium dodecyl sulphate (SDS) M greater than or equal to 10(-3)). The C3(N) and C3(D) subsets are labile and are expressed by native and denatured C3, respectively. Antisera to native C3, anti-C3(S-N), react with the C3(S) as well as the C3(N) subset. Antisera to isolated C3 subunits react exclusively with the C3(D) subset. A separation of anti-C3(S) and anti-C3(N) antibodies was accomplished by adsorbing the anti-C3(S-N) antiserum with insolubilized, denatured C3, anti-C3(N) antibodies remained unadsorbed. Anti-C3(S) antibodies were adsorbed and subsequently eluted from the denatured C3. Agglutination studies with EAC1423b cells showed significant agglutination with anti-C3(S) and anti-C3(D) antisera but reduced agglutination with anti-C3(N) antisera. Agglutination by anti-C3(D) antisera was unaffected in the presence of EDTA serum containing converted or unconverted C3. These data suggest an antigenic modification of C3b-b' upon binding that mirrors the antigenic transition associated with SDS denaturation of C3.     

Eutectic phase behavior of 1-stearoyl-2-caprylphosphatidylcholine and dimyristoylphosphatidylcholine mixtures

The thermotropic behavior of aqueous dispersions of C(18):C(10)PC/diC(14)PC mixtures with different molar ratios has been investigated by high-resolution differential scanning calorimetry. C(18):C(10)PC is a highly asymmetric lipid molecule, whereas diC(14)PC is a symmetric species with the same molecular weight. Their packing properties in the bilayer are known to be similar at T greater than Tm, but very dissimilar at T less than Tm. Calorimetric results indicate that C(18):C(10)PC and diC(14)PC are completely miscible in the liquid-crystalline state. In the gel state, however, C(18):C(10)PC and diC(14)PC are only partially miscible. The temperature-composition phase diagram for C(18):C(10)PC/diC(14)PC mixtures has the shape characteristic of a typical eutectic system.     

Binary mixtures of saturated and unsaturated mixed-chain phosphatidylcholine. A differential scanning calorimetry study

High-resolution differential scanning calorimetry (DSC) has been used to study the aqueous dispersions of mixed-chain phosphatidylcholines prepared from colyophilized mixtures of C(18):C(11:1 delta 10) PC/C(18):C(10)PC and C(18):C(11:1 delta 10) PC/C(18):C(11)PC of various molar ratios. These mixed-chain phospholipids are characterized by a marked disparity in their acyl-chain lengths; however, the sn-1 acyl chain in the fully extended conformation is about twice as long as the sn-2 acyl chain. Their thermotropic behavior was determined, and the phase diagrams of these two mixtures were constructed from the calorimetric data. Results indicate that C(18):C(11:1 delta 10)PC/C(18):C(10)PC and C(18):C-(11:1 delta 10)PC/C(18):C(11)PC are miscible in all proportions with a near-ideal behavior of mixing in the gel and liquid-crystalline phases. Equimolar mixtures of diC(14)PC/C(18):C(11:1 delta 10)PC, diC(14)PC/C(18):C(10)PC, and diC(14)PC/C(18):C(11)PC have also been studied by DSC. These phosphatidylcholines in the 1:1 mixture differ in Tm by less than 11 degrees C; however, they exhibit gel-phase immiscibility in the plane of the bilayer. Taken together, these studies suggest that C(18):C(11)PC and C(18):C(11:1 delta 10)PC are packed similarly to C(18):C(10)PC in excess water as mixed interdigitated bilayers, at T less than Tm, which transform into partially interdigitated bilayers when heated above Tm.     

Probing the ethanol-induced chain interdigitations in gel-state bilayers of mixed-chain phosphatidylcholines

Using high-resolution differential scanning calorimetry (DSC), we have studied the effects of ethanol concentrations, [EtOH], on the main phase transition temperatures (T[m]) of the following mixed-chain phosphatidylcholines (PCs): C(15):C(17)PC, C(17):C(15)PC, and C(12):C(20)PC. These lipids have a common molecular weight; however, their apparent acyl chain-length differences between the sn-1 and sn-2 acyl chains, delta C, are distinctively different. The delta C values for these three mixed-chain PCs are, respectively, 0.5, 3.5, and 6.5 C-C bond lengths. DSC results show that the T(m) profiles for C(15):C(17)PC and C(17):C(15)PC bilayers in the plot of T(m) versus [EtOH] are V-shaped biphasic curves, with the minimum T(m) occurring at 50 and 73 mg/ml of ethanol, respectively. In contrast, the C(12):C(20)PC bilayer exhibits a nearly linear decrease in T(m) with increasing [EtOH]. In addition, x-ray diffraction experiments were also performed to assess the structural changes of these three mixed-chain PCs in the gel-state bilayers, at 20 degrees C, in response to high concentrations of ethanol. X-ray diffraction data indicate that, in the absence of ethanol, these three lamellar lipids are all packed in the normal (L beta') gel phase in aqueous media. In the presence of 120 mg/ml of ethanol, however, the C(15):C(17)PC and C(17):C(15)PC lamellae are packed in the fully interdigitated (L beta[I]) gel phase. The V-shaped T(m) curves detected calorimetrically for these two lipids in response to [EtOH] can thus be explained by the ethanol-induced L beta' --> L beta[I] isothermal phase transition. Interestingly, the results of x-ray diffraction study reveal, for the first time, that an ethanol-induced L beta' --> L(MI) (mixed interdigitated phase) isothermal phase transition occurs in the gel-state bilayer of highly asymmetrical C(12):C(20)PC. Therefore, the chain asymmetry is recognized to play an important role in the ethanol-induced chain interdigitation at T < T(m).