Genome sequence of Halobacterium species NRC-1

We report the complete sequence of an extreme halophile, Halobacterium sp. NRC-1, harboring a dynamic 2,571,010-bp genome containing 91 insertion sequences representing 12 families and organized into a large chromosome and 2 related minichromosomes. The Halobacterium NRC-1 genome codes for 2,630 predicted proteins, 36% of which are unrelated to any previously reported. Analysis of the genome sequence shows the presence of pathways for uptake and utilization of amino acids, active sodium-proton antiporter and potassium uptake systems, sophisticated photosensory and signal transduction pathways, and DNA replication, transcription, and translation systems resembling more complex eukaryotic organisms. Whole proteome comparisons show the definite archaeal nature of this halophile with additional similarities to the Gram-positive Bacillus subtilis and other bacteria. The ease of culturing Halobacterium and the availability of methods for its genetic manipulation in the laboratory, including construction of gene knockouts and replacements, indicate this halophile can serve as an excellent model system among the archaea.

Involvement of phospholipase D in wound-induced accumulation of jasmonic acid in arabidopsis

Multiple forms of phospholipase D (PLD) were activated in response to wounding, and the expressions of PLDalpha, PLDbeta, and PLDgamma differed in wounded Arabidopsis leaves. Antisense abrogation of the common plant PLD, PLDalpha, decreased the wound induction of phosphatidic acid, jasmonic acid (JA), and a JA-regulated gene for vegetative storage protein. Examination of the genes involved in the initial steps of oxylipin synthesis revealed that abrogation of the PLDalpha attenuated the wound-induced expression of lipoxygenase 2 (LOX2) but had no effect on allene oxide synthase (AOS) or hydroperoxide lyase in wounded leaves. The systemic induction of LOX2, AOS, and vegetative storage protein was lower in the PLDalpha-suppressed plants than in wild-type plants, with AOS exhibiting a distinct pattern. These results indicate that activation of PLD mediates wound induction of JA and that LOX2 is probably a downstream target through which PLD promotes the production of JA.

Lipid domains in model and biological membranes

Lipid domains that occur within biological of model membranes encompass a variety of structures with very different lifetimes. The separation of membrane lipids into compositional domains can be due to lateral phase separation, immiscibility within a single phase, or interaction of lipids with integral or peripheral proteins. Lipid domains can affect the extent and rate of reactions in the membrane and provide sites for the activity of specialized proteins. Domains are likely to be involved in the process of lipid sorting to various cellular membranes, as well as in other processes which involve membrane budding or invagination.

Sensitivity of sorghum pollen and pistil to high-temperature stress

High temperature (HT) decreases seed set percentage in sorghum (Sorghum bicolor [L.] Moench). The relative sensitivity of pollen and particularly pistil and the mechanistic response that induces tolerance or susceptibility to HT are not well known and hence are the major objectives of this research. The male sterile (ATx399) and fertile (RTx430) lines were exposed to 30/20 °C (optimum temperature), 36/26 °C (HT1 ), and 39/29 °C (HT2 ) from the start of booting to seed set in a controlled environment. Similarly, in the field, HT stress was imposed using heat tents. HT stress decreased pollen germination. Relatively high levels of reactive oxygen species and decreased antioxidant enzyme activity and phospholipid unsaturation were observed in pollen compared to pistil under HT. The severe cell organelle damage was observed in pollen and pistil at 36/26 and 39/29 °C, respectively. The seed set percentage was higher in HT-stressed pistil pollinated with optimum-temperature pollen. Direct and reciprocal crosses indicate that pollen was more sensitive with larger decreases in seed set percentage than pistil under HT stress. The negative impact was greater in pollen than pistil at lower temperatures. Overall, pollen was more sensitive than pistil to HT stress because it is more susceptible to oxidative damage than pistil.

Decreased photosynthetic rate under high temperature in wheat is due to lipid desaturation, oxidation, acylation, and damage of organelles

BACKGROUND

High temperature is a major abiotic stress that limits wheat (Triticum aestivum L.) productivity. Variation in levels of a wide range of lipids, including stress-related molecular species, oxidative damage, cellular organization and ultrastructural changes were analyzed to provide an integrated view of the factors that underlie decreased photosynthetic rate under high temperature stress. Wheat plants of cultivar Chinese Spring were grown at optimum temperatures (25/15 °C, maximum/minimum) until the onset of the booting stage. Thereafter, plants were exposed to high temperature (35/25 °C) for 16 d.

RESULTS

Compared with optimum temperature, a lower photosynthetic rate was observed at high temperature which is an interplay between thylakoid membrane damage, thylakoid membrane lipid composition, oxidative damage of cell organelle, and stomatal and non-stomatal limitations. Triacylglycerol levels were higher under high temperature stress. Polar lipid fatty acyl unsaturation was lower at high temperature, while triacylglycerol unsaturation was the same at high temperature and optimum temperature. The changes in lipid species indicates increases in activities of desaturating, oxidizing, glycosylating and acylating enzymes under high temperature stress. Cumulative effect of high temperature stress led to generation of reactive oxygen species, cell organelle and membrane damage, and reduced antioxidant enzyme activity, and imbalance between reactive oxygen species and antioxidant defense system.

CONCLUSIONS

Taken together with recent findings demonstrating that reactive oxygen species are formed from and are removed by thylakoid lipids, the data suggest that reactive oxygen species production, reactive oxygen species removal, and changes in lipid metabolism contribute to decreased photosynthetic rate under high temperature stress.

Partition of amphiphilic molecules into phospholipid vesicles and human erythrocyte ghosts: measurements by ultraviolet difference spectroscopy

Molar partition coefficients for chlorpromazine and methochlorpromazine between phospholipid vesicles or human erythrocyte ghosts and buffer are determined by ultraviolet difference spectroscopy. The partition coefficients between small unilamellar egg phosphatidylcholine vesicles and buffer at pH 7.4 are 4.4 X 10(5) for chlorpromazine and 0.8 X 10(5) for methochlorpromazine, determined with 10 microM amphiphile. An increase in the partition of chlorpromazine into vesicles is seen as the pH is increased to the pKa of chlorpromazine at 9.2. Chlorpromazine also partitions preferentially into fluid-phase phospholipid compared to solid-phase phospholipid. Molar partition coefficients between unsealed human erythrocyte ghosts and buffer at pH 8.0 with 10 microM amphiphile are determined to be 6.5 X 10(5) for chlorpromazine and 2.5 X 10(5) for methochlorpromazine. Difference spectroscopy is an equilibrium technique that does not require separation of bound from free amphiphile, as do many other methods of determining membrane-buffer partition coefficients. This method is useful for any amphiphile that has an appreciable absorbance below its critical micelle concentration and whose absorbance is sensitive to environment.

In vivo substrates and the contribution of the common phospholipase D, PLDalpha, to wound-induced metabolism of lipids in Arabidopsis

The common plant phospholipase D (PLD), PLDalpha, has been proposed to be involved in wound-induced production of jasmonic acid. To better understand the role(s) of PLDalpha in the wound response, detailed lipid analysis was carried out to determine the in vivo substrates and the contribution of PLDalpha in wound-induced lipid metabolism in Arabidopsis thaliana. Mechanical wounding of Arabidopsis leaves resulted in significantly less hydrolysis of phosphatidylcholine (PC) in PLDalpha-deficient than in wild-type plants. Hydrolysis of phosphatidylethanolamine, phosphatidylglycerol (PG), and phosphatidylinositol within 30 min of wounding was not significantly different in PLDalpha-deficient and wild-type leaves. Phosphatidic acid (PA) levels increased rapidly in wild-type and, to a lesser extent, in PLDalpha-deficient plants. The acyl composition of the PA generated by wounding suggests that the major in vivo substrate of PLD in wild-type leaves was PC, and that PG hydrolysis accounted for 10-15% of the wound-induced PA in wild-type leaves. Comparison of the acyl compositions of the wound-induced PA of wild-type and PLDalpha-deficient leaves indicated that PLDalpha hydrolyzed PG more readily than other PLD isoforms did. Wounding produced substantial increases in free linoleic and linolenic acids in wild-type plants, whereas PLDalpha-deficient plants showed only a slight increase in linoleic acid and no significant increase in linolenic acid. These results demonstrate that PLDalpha and at least one other PLD isoform, as well as other hydrolytic enzymes, are active in mechanically wounded Arabidopsis leaves, and PLDalpha is involved in wound-induced metabolism of polyunsaturated fatty acids.

Partition of parinaroyl phospholipid probes between solid and fluid phosphatidylcholine phases

The partitioning of parinaroyl phospholipid probes between solid- and fluid-phase phospholipid is examined. The immiscible model system dipalmitoylphosphatidylcholine and palmitoyldocosahexaenoylphosphatidylcholine is used. Fluorescence quantum yields and fluorescence polarization are used to calculate Kps/f, the solid to fluid phase partition coefficient of each probe [Sklar, L. A., Miljanich, G. P. & Dratz, E. A. (1979) Biochemistry 18, 1707-1716]. Like free trans-parinaric acid (9,11,13,15-all-trans-octadecatetraenoic acid) 1-palmitoyl-2-trans-parinaroylphosphatidylcholine and 1-palmitoyl-2-tra-parinaroylphosphatidylethanolamine partition strongly into solid phase with mean Kps/fs of 7 +/- 4 and 9 +/- 5, respectively. Like free cis-parinaric acid (9,11,13,15-cis-trans,trans,cis-octadecatetraenoic acid), another group of phospholipid probes prefer fluid phase just slightly or partition equally between fluid and solid phases. The Kps/f of 1-palmitoyl-2-cis-parinaroylphosphatidylcholine is 0.6 +/- 0.2, that of 1-palmitoyl-2-cis-parinaroylphosphatidylethanolamine is 1.0 +/- 0.3, that of 1-oleoyl-2-trans-parinaroylphosphatidylcholine is 0.6 +/- 0.3, and that of 1-oleoyl-2-trans-parinaroylphosphatidylethanolamine is 0.7 +/- 0.3. Two probes partition more strongly into fluid-phase phospholipid. These are 1-oleoyl-2-cis-parinaroylphosphatidylcholine with a Kps/f of 0.2 +/- 0.1 and 1-oleoyl-2-cis-parinaroylphosphatidylethanolamine with a Kps/f of 0.4 +/- 0.4.

Coronary artery reoperations. Early and late results in 101 patients

Coronary artery reoperation was performed on 101 patients between 1972 and 1985. The resternotomy was associated with major hemorrhage in 12 cases. Of 29 patent internal mammary artery (IMA) grafts, 11 (38%) were damaged during mobilization of the left ventricle. At reoperations performed more than a year after the initial operation, increased graft blood flow compared with the first operation was observed in IMA but not in vein grafts. There were six early deaths (6%). The 5-year survival rate, inclusive of early mortality, was 90%. After a median of 2.5 years, 82% of the patients reported symptomatic improvement and 22% were completely free from angina, but full physical fitness was restored in only 3%. Excluding the patients of retirement age, 35% were able to resume work after the reoperation. Coronary artery reoperation should be considered only for patients with severe angina, because of the increased surgical risk and the lower likelihood of completely relieved symptoms. Presence of a patent IMA graft necessitates special caution.

A comparative study of lipid compositions of Cryptosporidium parvum (Apicomplexa) and Madin-Darby bovine kidney cells

Membrane lipid compositions of Cryptosporidium parvum and Madin-Darby bovine kidney cells, an epithelial-like cell line commonly used to study coccidia in vitro, were analyzed using both thin-layer chromatography and gas-liquid chromatography. Phosphatidylcholine was the predominant lipid in both C. parvum and Madin-Darby bovine kidney cells, comprising 65% and 41% of the total phospholipids, respectively. Phospholipids of C. parvum contained twice the level of 16:0 and twenty-fold more 18:2 than the Madin-Darby bovine kidney cell line. We suggest that the parasite may be capable of sequestering specific complex membrane lipids at concentrations greater than those in the host cells. This study constitutes the first report of the lipid composition of C. parvum.

Role of albumin as a fatty acid carrier for biosynthesis of lens lipids

Although serum albumin is the major protein component of the aqueous humor and vitreous humor, its possible physiological role(s) in lens metabolism has not yet been determined. BODIPY fatty acid, a fluorescent analogue of a C(12) long chain fatty acid, was bound to serum albumin, then incubated with lenses in culture. After various times of incubation, the lenses were homogenized, lipids extracted, and the extracted lipids resolved by thin layer chromatography. Fluorescence analyses demonstrated that the BODIPY fatty acid--albumin complex was translocated into the lens, where the BODIPY fatty acid was incorporated in a time dependent manner into numerous lipids, including phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin. Together, the results strongly suggest that serum albumin in the aqueous humor and/or vitreous humor facilitates the translocation of long chain fatty acids into the lens, where they are used for the biosynthesis of lens lipids.

Partition of parinaroyl phospholipids in mixed head group systems

Partitioning of 1-palmitoyl-2-cis-parinaroylphosphatidylcholine, 1-palmitoyl-2-cis-parinaroylphosphatidylethanolamine, 1-oleoyl-2-trans-parinaroylphosphatidylcholine, and 1-oleoyl-2-trans-parinaroylphosphatidylethanolamine between solid-phase phosphatidyelthanolamine and between solid-phase phosphatidylcholine and fluid-phase phosphatidylethanolamine is investigated. The partitioning of these probes is shown to be nearly independent of their head group. Fluorescence polarization of the above probes plus trans-parinaric acid, cis-parinaric acid, 1-palmitoyl-2-trans-parinaroylphosphatidylcholine, 1-oleoyl-2-cis-parinaroylphosphatidylcholine, and 1-oleoyl-2-cis-parinoylphosphatidylethanolamine is examined in phospholipids isolated from LM cell (mouse fibroblast) plasma membranes. A fraction of these phospholipids undergoes a gel-liquid-crystalline phase transition beginning near the physiological temperature. The parinaroyl probes with the highest solid-fluid-phase partition coefficients [Welti, R., & Silbert, D. F. (1982) Biochemistry (preceding paper in this issue)] detect the transition most readily. The degree of response to this transition also appears to depend on the acyl chains of the parinaroyl phospholipid rather than the probe head group. This is further demonstrated with the phosphatidylcholine and phosphatidylethanolamine fractions from LM cell plasma membranes.

Thermotropic behavior of mixtures of glycosphingolipids and phosphatidylcholine: effect of monovalent cations on sulfatide and galactosylceramide

The thermotropic behavior of both sulfatide (3-sulfogalactosylceramide) and galactosylceramide in dielaidoylphosphatidylcholine (DEPC) liposomes was studied, using steady-state fluorescence polarization of parinaric acid isomers. The glycosphingolipid (GSL) concentration of the liposomes was varied from 0 to 100%, and phase diagrams were constructed. The data indicate that sulfatide and DEPC are immiscible in the gel phase at sulfatide mole ratios of less than 0.30. The temperature of onset of the gel-liquid-crystalline phase transition is higher in K+ -containing buffer than in osmotically equal Na+ -containing buffer. Similar measurements, using galactosylceramide, a neutral GSL, indicated that this lipid and DEPC are immiscible in the gel phase at galactosylceramide mole ratios of less than 0.40. In contrast to the results obtained with sulfatide, onset temperatures are identical in Na+- or K+-containing buffers. The phase properties of sulfatide/DEPC mixtures are shown to depend on the cation only when the sulfatides contain hydroxy fatty acids. Our observations indicate that physiologically relevant concentrations of monovalent cations affect motion and distribution of sulfatide in biological membranes and further implicate this GSL as an important determinant of function of the Na+,K+-ATPase. A preliminary report of these data [Rintoul, D.A., Welti, R., & Song, W. (1988) Biophys. J. 53, 126a].

Coronary endarterectomy--angiographic and clinical results

Of 75 patients who underwent coronary endarterectomy, 16% had left main stem stenosis, 4% one-vessel, 27% two-vessel and 53% three-vessel disease. On average 2.9 grafts per patient were inserted, in conjunction with 82 manual endarterectomies (38 right coronary, 35 left anterior descending, 9 circumflex branches). In 68/75 cases (91%) the endarterectomy was not preplanned and in 39 cases (52%) greater than or equal to 3 cm of the atherosclerotic core was removed. All four early deaths (5%) followed endarterectomy of LAD. Acute perioperative myocardial infarction was confirmed in 19% and probable in further 8%. At angiography 1-139 (median 25) months postoperatively, all three internal mammary artery grafts and 19/34 saphenous vein grafts (56%) to endarterectomized vessels were patent, though in 4 of the 19, the coronary artery was occluded distal to the anastomosis. In addition 17/18 conventional internal mammary artery (94%) and 48/59 conventional saphenous vein grafts (81%) were patent. The vein graft patency rate was not significantly influenced by postoperative anticoagulant therapy, but was significantly increased among patients with relief of angina: 44% reported freedom from angina and 92% at least some relief after a median of 3 years. The 5-year and 10-year survival rates were 85% and 68%. Despite the increased risk, endarterectomy can be recommended for severely diseased major coronary arteries.

Early mortality after 2,902 coronary artery bypass operations

A review of 2,902 coronary artery bypass grafting operations is presented. During the 16-year study period the mean patient age rose from 51 to 59 years and the average number of grafts per patient from 1.5 to 3.0. There were 81 early deaths (2.8%, the most common cause being myocardial infarction (68%). Left main stem stenosis was present in 23 of these 81 patients and depressed left ventricular function in 30. Compared with the survivors, the deceased patients were characterized by higher age, proportionately large numbers of women, combined procedures and reoperations and less use of internal mammary artery grafts. Of the 94 patients aged greater than or equal to 70, 11 died (12%). The perioperative mortality was significantly greater (p less than 0.05) in women than in men (20/457 vs. 61/2445 viz. 4.4% vs. 2.5%). Combined operations were associated with 8.7% (27/311), reoperations with 6% (6/101) and coronary endarterectomy with 5% (4/75) early deaths. In the last year of the study there were three early deaths among 359 patients (0.8%) who underwent primary isolated coronary bypass grafting without endarterectomy. The perioperative risks fell steadily during 16 years, despite rising proportions of older patients, combined procedures, reoperation and coronary endarterectomy.

Membrane penetration depth and lipid phase preference of acyl-labeled dansyl phosphatidylcholines in phosphatidylcholine vesicles

The dansyl fluors of 1-oleoyl-2-[4-(dansyl)amino]butyl]-sn-glycero-3-phosphocholine (18:1,4-dansyl PC) and 1-palmitoyl-2-[1-[(dansyl)amino)]undecanoyl]-sn-glycero-3-phosphoc holine (16:0,11-dansyl PC) were shown to reside at similar depths in phosphatidylcholine vesicles at pH 7. Analysis of fluorescence emission maxima showed that the dansyl groups of both 18:1,4-dansyl PC and 16:0,11-dansyl PC in phosphatidylcholine vesicles experienced environments more polar than methanol, suggesting that the dansyl group attached to the terminus of the undecanoyl chain must fold back toward the bilayer surface. Fluorescence polarization measurements in solid/fluid lipid mixtures show that both probes partition strongly into fluid phase lipid. The very low polarization values of 16:0,11-dansyl PC in lipid vesicles are consistent with the notion that the dansyl fluor of 16:0,11-dansyl PC existed in an environment allowing a high degree of motional freedom due to folding back of the dansyl group attached to the undecanoyl chain.

Coronary artery bypass grafting in patients 70 years of age and older. Early and late results

Ninety-four patients 70 years of age and older underwent coronary artery bypass grafting (CABG) between 1979 and 1985. Thirty-two percent were females. An internal mammary artery was used in 49% and concomitant cardiac procedures were performed in 51% of the operations. Early mortality was 12%. Five of 11 early deaths were from non-cardiac causes: ascending aortic disease (2), cerebral damage (2) and septicaemia (1). Postoperative morbidity included neurological complications in 16%, reoperation for bleeding in 12%, mediastinitis or sternal dehiscence in 4% and perioperative acute myocardial infarction in 4%. At follow-up, a median of 2.5 years after surgery, 83% were completely free from angina, 5% much improved, 9% improved and 3% had unchanged symptoms of angina. Actuarial survival, inclusive of early mortality, was 84% at 3 years. Female sex and concomitant cardiac surgery were common in elderly patients who had CABG. Early mortality from noncardiac causes and postoperative morbidity were increased but dramatic relief of symptoms was achieved in the majority of survivors.

Synthesis and characterization of N-parinaroyl analogs of ganglioside GM3 and de-N-acetyl GM3. Interactions with the EGF receptor kinase

A specific plasma membrane glycosphingolipid, known as ganglioside GM3, can regulate the intrinsic tyrosyl kinase activity of the epidermal growth factor (EGF) receptor; this modulation is not associated with alterations in hormone binding to the receptor. GM3 inhibits EGF receptor tyrosyl kinase activity in detergent micelles, in plasma membrane vesicles, and in whole cells. In addition, immunoaffinity-purified EGF receptor preparations contain ganglioside GM3 (Hanai et al. (1988) J. Biol. Chem. 263, 10915-10921), implying that the glycosphingolipid is intimately associated with the receptor kinase in cell membranes. Both the nature of this association and the molecular mechanism of kinase inhibition remain to be elucidated. In this report, we describe the synthesis of a fluorescent analog of ganglioside GM3, in which the native fatty acid was replaced with trans-parinaric acid. This glycosphingolipid inhibited the receptor kinase activity in a manner similar to that of the native ganglioside. A modified fluorescent glycosphingolipid, N-trans-parinaroyl de-N-acetyl ganglioside GM3, was also prepared. This analog, like the nonfluorescent de-N-acetyl ganglioside GM3, had no effect on receptor kinase activity. Results from tryptophan fluorescence quenching and steady-state anisotropy measurements in membranes containing these fluorescent probes and the human EGF receptor were consistent with the notion that GM3, but not de-N-acetyl GM3, interacts specifically with the receptor in intact membranes.

Lipid arrangement in fluid model membranes: analysis by cross-linking of phosphatidylethanolamines

Binary mixtures of fluid phase phosphatidylethanolamines at pH 10 were treated with the bifunctional cross-linking reagent dimethylsuberimidate. Analysis of the dimeric species formed demonstrated that the phospholipid species in dimyristoylphosphatidylethanolamine/dielaidoylphosphatidylethanolamine mixtures at 52 degrees C and dielaidoylphosphatidylethanolamine/dilauroylphosphatidylethanolamine mixtures at 41 degrees C were randomly arranged. Analysis of the dimeric species formed in dipalmitoylphosphatidylethanolamine/dioleoylphosphatidylethanolamine mixtures at 68 degrees C showed that this mixture was very close to being randomly arranged, with just a slight propensity of like phospholipid species to cluster.

Partition of parinaroylphosphatidylethanolamines and parinaroylphosphatidylglycerols in immiscible phospholipid mixtures

Partitioning of two parinaroyl phosphatidylethanolamines and two parinaroyl phosphatidylglycerols between solid and fluid phase phospholipids was examined. Fluorescence quantum yields and fluorescence polarization measurements were used to calculate Ks/fp, the solid to fluid partition coefficient of each probe (Sklar, L.A., Miljanich, G.P. and Dratz, E.A. (1979) Biochemistry 18, 1707-1716). In the immiscible mixture dipalmitoylphosphatidylcholine and dilinoleylphosphatidylcholine, both 1-palmitoyl-2-trans-parinaroylphosphatidylethanolamine and 1-palmitoyl-2-transparinaroylphosphatidylglycerol partitioned preferentially into solid phase lipid with mean Ks/fp values (calculated from quantum yields) of 3.4 +/- 1.5 and 2.1 +/- 0.7, respectively. In contrast, 1-oleoyl-2-cis-parinaroylphosphatidylethanolamine and 1-oleoyl-2-cis-parinaroylphosphatidylglycerol partitioned preferentially into fluid phase lipid in the same model system with mean Ks/fp values (calculated from quantum yields) of 0.44 +/- 0.26 and 0.16 +/- 0.07, respectively. Fluorescence polarization data on the same four parinaroyl phospholipids in mixtures of solid-phase dimyristoylphosphatidyl ethanolamine and fluid-phase dilinoleoylphosphatidylglycerol were similar to those obtained in the immiscible phosphatidylcholine system, demonstrating that the partitioning of these probes is not strongly dependent on head group. Knowledge of the partition properties of these fluorescent probes is relevant to use of these probes in investigation of the phase behavior of Escherichia coli inner membrane lipids, since phosphatidylethanolamine and phosphatidylglycerol species account for approximately 95% of these lipids.

General kinetic model for protein-mediated phospholipid transfer between membranes

Phospholipid transfer protein catalyzes the transfer of phospholipids between bilayer membranes. A general model is developed for describing the kinetics of this process. While previous models derive detailed expressions only for the initial rate of transfer from donor to acceptor membranes, this model takes into account donor-to-donor, acceptor-to-acceptor, and acceptor-to-donor transfers, in addition to the usual donor-to-acceptor transfer. The apparent rate of transfer along any of these specific routes is given as the product of the total rate of transfer (the sum of the rates of transfer along all four routes) and a probability function uniquely defined for each route. The model explains adequately the effects of membrane concentration on phospholipid transfer activity as well as the consequences of varying membrane surface charge and size. Using bovine liver phosphatidylcholine transfer protein, the model is applied to the kinetic analysis of phosphatidylcholine transfer between two populations of small unilamellar vesicles. Rates of protein-catalyzed phosphatidylcholine transfer between vesicles with identical phosphatidic acid content (2 or 6 mol%) are determined experimentally as a function of total vesicle concentration to calculate apparent dissociation constants and maximum rates of transfer; apparent rates of transfer between various combinations of vesicles containing 2 or 6 mol% phosphatidic acid are then deduced from the derived velocity expression. Reasonably good agreement is seen between theoretical apparent rate-vesicle concentration relationships and those measured experimentally. The results support the general treatment of the kinetics of protein-mediated phospholipid transfer and permit an estimation of useful kinetic parameters.

Cross-linking of phosphatidylethanolamine neighbors with dimethylsuberimidate is sensitive to the lipid phase

Dimethylsuberimidate was reacted with aqueous dispersions of dipalmitoylphosphatidylethanolamine, dimyristoylphosphatidylethanolamine, dilauroylphosphatidylethanolamine, and dielaidoylphosphatidylethanolamine at pH 10 and at pH 8. The amount of amidine dimer formation was about four times greater above the gel-to-fluid phase transition of each lipid than below the transition. The transition temperature of each phosphatidylethanolamine, measured by steady-state fluorescence anisotropy of cis-parinaric acid, was lower at pH 10 than at pH 8 or in water. The ability of dimethylsuberimidate to discriminate between phosphatidylethanolamines in the fluid and gel phases should allow use of this reagent to identify phosphatidylethanolamine species within the gel or fluid lipid phase.

Analysis of dimeric species derived from the reaction of phosphatidylethanolamine with dimethylsuberimidate

Phosphatidylethanolamines of various fatty acyl species in vortexed lipid dispersions were reacted with dimethylsuberimidate to produce dimeric products. The yield was 34% at pH 10 and 2% at pH 7. The crosslinked phosphatidylethanolamine species were separated from minor products and the reactants by extraction and two-dimensional thin-layer chromatography on silica gel G, gel filtration on lipophilic Sephadex, or C18-reversed phase high-performance liquid chromatography (HPLC). Reversed phase HPLC was also used to resolve the dimers into individual molecular species. Analysis of the dimers revealed the extinction coefficients at 205 nm to be higher than those of the reactant phosphatidylethanolamines. Proton nuclear magnetic resonance spectroscopy and chemical analysis implied that the dimers contain an amidine group.

Arrangement of phosphatidylethanolamine molecular species in Escherichia coli membranes and reconstituted lipids as determined by dimethyl suberimidate cross-linking of nearest neighbor lipids

Dimethylsuberimidate cross-linking has been used to determine the arrangement of phosphatidylethanolamine (PE) molecular species in Escherichia coli membranes. No large deviations from random mixing were found in wild-type strain AB1623, either in whole cells or in extracted lipids which were reconstituted into multilamellar vesicles. These results suggest, first, that there is little difference in the PE molecular species composition of the three lipid monolayers (the inner and outer monolayers of the inner membrane and the inner monolayer of the outer membrane) which contain significant amounts of PE. Secondly, the results suggest that the molecular species within each monolayer and in the extracted lipids are arranged close to randomly with no tendency for like molecular species to cluster. E. coli strain L8-2, which has a defect in beta-oxidation and a temperature-sensitive mutation in total fatty acid synthesis, was grown on cis-vaccenate (cis-11,12- octadecenate) to enrich the cells in divaccenoyl PE. Again, in whole cells or in lipids extracted from whole cells and reconstituted into multilamellar vesicles, the species were close to randomly arranged. However, a consistent, slight tendency of divaccenoyl species to pair with like species as compared to pairing with the second most common species, vaccenoyl, palmitoleoyl PE, was noted in both extracted lipids and in whole cells.