Center of pressure (COP) during the Postural Balance Control of High-Heeled Woman

This study addressed the effect of balance control problems of the high-heeled women. Clinical relationships have been proposed linking foot ailments or pain to wearing high heels, yet little quantitative research has been done on the relationship between bare foot and high feeled foot. The purposes of this study were to objectively quantify the displacements and velocities of center-of- pressure (COP) of body during two-way waist pulling and to compare the differences between barefooted and high-heeled situations. We used a waist pulling system which has three different magnitudes to sway the subjects. We found that the kinematic information of barefooted and high-heeled women's COP is very important in understanding the mechanism of postural balance control of women in every-day life. In the high-heeled's case, the displacement of COP increases in 200% as against bare footed. Also the velocity variation of COP grows two times than the bare footed.

Hydrolysis of minor glycerophospholipids of plasma lipoproteins by human group IIA, V and X secretory phospholipases A2

We investigated the hydrolysis of the minor glycerophospholipids of human HDL(3), total HDL and LDL using human group IIA, V and X secretory phospholipases A(2) (sPLA(2)s). For this purpose we employed the enzyme and substrate concentrations and incubation times optimized for hydrolysis of phosphatidylcholine (PtdCho), the major glycerophospholipid of plasma lipoproteins. In contrast to PtdCho, which was readily hydrolyzed by group V and X sPLA(2)s, and to a lesser extent by group IIA sPLA(2), the minor ethanolamine, inositol and serine glycerophospholipids exhibited marked resistance to hydrolysis by all three sPLA(2)s. Thus, when PtdCho was hydrolyzed about 80%, the ethanolamine and inositol glycerophospholipids reached a maximum of 40% hydrolysis. The hydrolysis of phosphatidylserine (PtdSer), which was examined to a more limited extent, showed similar resistance to group IIA, V and X sPLA(2)s, although the group V sPLA(2) attacked it more readily than group X sPLA(2) (52% versus 39% hydrolysis, respectively). Surprisingly, the group IIA sPLA(2) hydrolysis remained minimal at 10-15% for all minor glycerophospholipids, and was of the order seen for the PtdCho hydrolysis by group IIA sPLA(2) at the 4-h digestion time. All three enzymes attacked the oligo- and polyenoic species in proportion to their mole percentage in the lipoproteins, although there were exceptions. There was evidence of a more rapid destruction of the palmitoyl compared to the stearoyl arachidonoyl glycerophospholipids. Overall, the characteristics of hydrolysis of the molecular species of the lipoprotein-bound diradyl GroPEtn, GroPIns and GroPSer by group V and X sPLA(2)s differed significantly from those observed with lipoprotein-bound PtdCho. As a result, the acidic inositol and serine glycerophospholipids accumulated in the digestion residues of both LDL and HDL, and presumably increased the acidity of the residual particles. An accumulation of the ethanolamine glycerophospholipids in the sPLA(2) digestion residues also had not been previously reported. These results further emphasize the diversity in the enzymatic activity of the group IIA, V and X sPLA(2)s. Since these sPLA(2)s possess comparable tissue distribution, their combined activity may exacerbate their known proinflammatory and proatherosclerotic function.

Differential hydrolysis of molecular species of lipoprotein phosphatidylcholine by groups IIA, V and X secretory phospholipases A2

Human groups IIA, V and X secretory phospholipases A2 (sPLA2s) were incubated with human HDL3, total HDL and LDL over a range of enzyme and substrate concentrations and exposure times. The residual phosphatidylcholines (PtdChos) were assayed by high performance liquid chromatography with electrospray ionization mass spectrometry (LC/ESI-MS). The enzymes varied markedly in their rates of hydrolysis of the different molecular species and in the production of lysoPtdCho. The sPLA2s were compared at a concentration of 1 microg/ml and an incubation time of 4 h, when all three enzymes showed significant activity. The groups V and X sPLA2 were up to 20 times more reactive than group IIA sPLA2. Group X sPLA2 hydrolyzed arachidonate and linoleate containing species preferentially, while group V hydrolyzed the linoleates in preference to polyunsaturates. In all instances, the arachidonoyl and linoleoyl palmitates were hydrolyzed in preference to the corresponding stearates by group X sPLA2. The group IIA enzyme appeared to hydrolyze randomly all diacyl molecular species. The minor alkylacyl and alkenylacyl glycerophosphocholines (GroPChos) were poor substrates for groups V and X sPLA2s and these phospholipids tended to accumulate. The present study demonstrates a preferential release of arachidonate from plasma lipoprotein PtdCho by group X sPLA2, as well as a relative resistance of polyunsaturated PtdChos to hydrolysis by group V enzyme, which had not been previously documented. The use of lipoprotein PtdCho as substrate with LC/ESI-MS identification of hydrolyzed molecular species eliminates much of the uncertainty about sPLA2 specificity arising from past analyses of fatty acid release from unknown or ill-defined sources.

Absolute electronic excitation cross sections for low-energy electron (5–12eV) scattering from condensed thymine

The absolute cross sections for electronic excitations of thymine by electron impact between 5 and 12 eV are determined by means of electron-energy loss (EEL) spectroscopy for the molecule deposited at submonolayer coverage on an inert Ar substrate. The lowest EEL features at 3.7 and 4.0 eV are attributed to the excitation of the triplet 1 3A'(pi --> pi*) and 1 3A''(n --> pi*) valence states of the molecule. The higher EEL features located at 4.9, 6.3, 7.3, and 9 eV with a weak shoulder around 6 eV are ascribed mostly to triplet valence (pi --> pi*) excitation manifold of the molecule. The energy dependence of the cross section for both the lowest triplet valence excitations shows essentially a peak at about 5 eV reaching a value of 2.9 x 10(-17) cm2. The cross sections for the higher EEL features are generally characterized by a common broad maximum around 8 eV. The latter reaches a value of 1.36 x 10(-16) cm2 for the combined 6 and 6.3 eV excitation region. The maxima in the present cross sections are found to correspond to the resonances that have been reported at about the same energies in the O- yield from electron impact on thymine in the gas phase.

Methylation of tumor suppressor gene p16 and prognosis of epithelial ovarian cancer

OBJECTIVE

Methylation of p16 promoter was evaluated in ovarian cancer to determine the role of p16 methylation in ovarian cancer prognosis.

METHODS

Two hundred and forty-nine patients with primary epithelial ovarian cancer were selected for the study; these patients were followed for a median of 31 months. Genomic DNA extracted from fresh frozen tumor tissues were treated with sodium bisulfite and were analyzed for p16 methylation using methylation-specific PCR (MSP). Cox regression survival analysis was performed to examine the associations of p16 methylation with progression-free and overall survivals.

RESULTS

Of the 249 patients, 100 (40%) were tested positive for p16 promoter methylation. The status of p16 methylation did not change significantly with patient age, disease stage, histological grade, residual tumor size, and debulking results, although p16 methylation seemed to occur more often in patients with advanced diseases or aggressive tumors. Compared to those without p16 methylation, patients with p16 methylation had significantly higher risk for disease progression (P = 0.01). The relative risk for progression was 1.69 (95% CI: 1.12-2.54), and the association remained statistically significant (RR = 1.54, 95% CI: 1.01-2.34) after adjusting for clinical and pathological variables. The risk for death was also higher in methylation positive patients than in methylation negative patients (RR = 1.33, 95% CI: 0.88-2.00), but the difference was not statistically significant.

CONCLUSION

The study suggests that promoter methylation in the p16 gene is associated with ovarian cancer progression, and evaluation of p16 methylation may have values in predicting ovarian cancer prognosis.

Habituation of an odorant-induced startle response in Drosophila

Habituation is a fundamental form of behavioral plasticity that permits organisms to ignore inconsequential stimuli. Here we describe the habituation of a locomotor response to ethanol and other odorants in Drosophila, measured by an automated high-throughput locomotor tracking system. Flies exhibit an immediate and transient startle response upon exposure to a novel odor. Surgical removal of the antennae, the fly's major olfactory organs, abolishes this startle response. With repeated discrete exposures to ethanol vapor, the startle response habituates. Habituation is reversible by a mechanical stimulus and is not due to the accumulation of ethanol in the organism, nor to non-specific mechanisms. Ablation or inactivation of the mushroom bodies, central brain structures involved in olfactory and courtship conditioning, results in decreased olfactory habituation. In addition, olfactory habituation to ethanol generalizes to odorants that activate separate olfactory receptors. Finally, habituation is impaired in rutabaga, an adenylyl cyclase mutant isolated based on a defect in olfactory associative learning. These data demonstrate that olfactory habituation operates, at least in part, through central mechanisms. This novel model of olfactory habituation in freely moving Drosophila provides a scalable method for studying the molecular and neural bases of this simple and ubiquitous form of learning.

Vibrational and electronic excitations of H[sub 2]O on thymine films induced by low-energy electrons

We investigated vibrational and electronic excitations of 0.1-layer up to 2.4-layer film of H(2)O deposited on a 1.4-layer film of thymine condensed on Ar at a temperature of 18 K using high-resolution electron-energy loss (EEL) spectroscopy at the incident energy of 12 eV. The spectral contribution originating essentially from the H(2)O overlayer is obtained by separating the measured contribution from the underlying film of thymine, considering the electron beam attenuation in the H(2)O overlayer. The vibrational EEL spectrum of submonolayer amount of H(2)O on thymine, which excepts for small energy shift of the vibrational bands, is found to compare in intensity to that of the same amount of H(2)O deposited directly on the argon. The electronic energy-loss intensity near 8.6 eV, which is attributed to the excitation of (3,1)B(1) states of H(2)O in condensed phase, is observed to decrease by a factor of about 3 by the presence of the underlying film of thymine. This indicates that the corresponding cross section for excitation the (3,1)B(1) states of H(2)O by the electron impact is reduced significantly by the close proximity of the thymine molecules.

Roles of calcium ions in the membrane binding of C2 domains

The C2 domain is a membrane-targeting domain found in many cellular proteins involved in signal transduction or membrane trafficking. The majority of C2 domains co-ordinate multiple Ca(2+) ions and bind the membrane in a Ca(2+)-dependent manner. To understand the mechanisms by which Ca(2+) mediates the membrane binding of C2 domains, we measured the membrane binding of the C2 domains of group IV cytosolic phospholipase A(2) (cPLA(2)) and protein kinase C-alpha (PKC-alpha) by surface plasmon resonance and lipid monolayer analyses. Ca(2+) ions mainly slow the membrane dissociation of cPLA(2)-C2, while modulating both membrane association and dissociation rates for PKC-alpha-C2. Further studies with selected mutants showed that for cPLA(2) a Ca(2+) ion bound to the C2 domain of cPLA(2) induces the intra-domain conformational change that leads to the membrane penetration of the C2 domain whereas the other Ca(2+) is not directly involved in membrane binding. For PKC-alpha, a Ca(2+) ion induces the inter-domain conformational changes of the protein and the membrane penetration of non-C2 residues. The other Ca(2+) ion of PKC-alpha-C2 is involved in more complex interactions with the membrane, including both non-specific and specific electrostatic interactions. Together, these studies of isolated C2 domains and their parent proteins allow for the determination of the distinct and specific roles of each Ca(2+) ion bound to different C2 domains.

Prevalence of the enteroaggregative Escherichia coli heat-stable enterotoxin 1 (EAST1) gene in isolates in weaned pigs with diarrhea and/or edema disease

A total of 476 Escherichia coli isolated from weaned pigs with diarrhea and/or edema disease were screened for the presence of the enteroaggregative E. coli heat-stable enterotoxin 1 (EAST1) gene by polymerase chain reaction (PCR). E. coli strains that carried EAST1 genes were also tested by PCR for the presence of genes for five fimbriae (F4, F5, F6, F18 and F41), two heat-stable (STa and STb) and one heat-labile (LT) enterotoxin, and Shiga toxin 2e (Stx2e). One hundred and forty nine (31.3%) of the 476 E. coli isolates carried the gene for EAST1. Of these 149 isolates, 66 (44.3%) carried the east1 gene only and 83 (55.7%) carried genes for the fimbrial adhesins or enterotoxins. E. coli which carried east1 gene also possessed genes for STa or F4 frequently. EAST1 may represent an additional determinant in the pathogenesis of E. coli diarrhea in weaned pigs.

Role of mitogen-activated protein kinase-mediated cytosolic phospholipase A2 activation in arachidonic acid metabolism in human eosinophils

The objective of this investigation was to determine the role of secretory and cytosolic isoforms of phospholipase A(2) (PLA(2)) in the induction of arachidonic acid (AA) and leukotriene synthesis in human eosinophils and the mechanism of PLA(2) activation by mitogen-activated protein kinase (MAPK) isoforms in this process. Pharmacological activation of eosinophils with fMLP caused increased AA release in a concentration (EC(50) = 8.5 nM)- and time-dependent (t(1/2) = 3.5 min) manner. Both fMLP-induced AA release and leukotriene C(4) (LTC(4)) secretion were inhibited concentration dependently by arachidonic trifluoromethyl ketone, a cytosolic PLA(2) (cPLA(2)) inhibitor; however, inhibition of neither the 14-kDa secretory phospholipase A(2) by 3-(3-acetamide-1-benzyl-2-ethylindolyl-5-oxy)propanephosphonic acid nor cytosolic Ca(2+)-independent phospholipase A(2) inhibition by bromoenol lactone blocked hydrolysis of AA or subsequent leukotriene synthesis. Pretreatment of eosinophils with a mitogen-activated protein/extracellular signal-regulated protein kinase (ERK) kinase inhibitor, U0126, or a p38 MAPK inhibitor, SB203580, suppressed both AA production and LTC(4) release. fMLP induced phosphorylation of MAPK isoforms, ERK1/2 and p38, which were evident after 30 s, maximal at 1-5 min, and declined thereafter. fMLP stimulation also increased cPLA(2) activity in eosinophils, which was inhibited completely by 30 microM arachidonic trifluoromethyl ketone. Preincubation of eosinophils with U0126 or SB203580 blocked fMLP-enhanced cPLA(2) activity. Furthermore, inhibition of Ras, an upstream GTP-binding protein of ERK, also suppressed fMLP-stimulated AA release. These findings demonstrate that cPLA(2) activation causes AA hydrolysis and LTC(4) secretion. We also find that cPLA(2) activation caused by fMLP occurs subsequent to and is dependent upon ERK1/2 and p38 MAPK activation. Other PLA(2) isoforms native to human eosinophils possess no significant activity in the stimulated production of AA or LTC(4).

Differential roles of ionic, aliphatic, and aromatic residues in membrane-protein interactions: a surface plasmon resonance study on phospholipases A2

The roles of cationic, aliphatic, and aromatic residues in the membrane association and dissociation of five phospholipases A(2) (PLA(2)), including Asp-49 PLA(2) from the venom of Agkistrodon piscivorus piscivorus, acidic PLA(2) from the venom of Naja naja atra, human group IIa and V PLA(2)s, and the C2 domain of cytosolic PLA(2), were determined by surface plasmon resonance analysis. Cationic interfacial binding residues of A. p. piscivorus PLA(2) (Lys-10) and human group IIa PLA(2) (Arg-7, Lys-10, and Lys-16), which mediate electrostatic interactions with anionic membranes, primarily accelerate the membrane association. In contrast, an aliphatic side chain of the C2 domain of cytosolic PLA(2) (Val-97), which penetrates into the hydrophobic core of the membrane and forms hydrophobic interactions, mainly slows the dissociation of membrane-bound protein. Aromatic residues of human group V PLA(2) (Trp-31) and N. n. atra PLA(2) (Trp-61, Phe-64, and Tyr-110) contribute to both membrane association and dissociation steps, and the relative contribution to these processes depends on the chemical nature and the orientation of the side chains as well as their location on the interfacial binding surface. On the basis of these results, a general model is proposed for the interfacial binding of peripheral proteins, in which electrostatic interactions by ionic and aromatic residues initially bring the protein to the membrane surface and the subsequent membrane penetration and hydrophobic interactions by aliphatic and aromatic residues stabilize the membrane-protein complexes, thereby elongating the membrane residence time of protein.

Mechanism of human group V phospholipase A2 (PLA2)-induced leukotriene biosynthesis in human neutrophils. A potential role of heparan sulfate binding in PLA2 internalization and degradation

Human group V phospholipase A(2) (hVPLA(2)) has been shown to have high activity to elicit leukotriene production in human neutrophils (Han, S. K., Kim, K. P., Koduri, R., Bittova, L., Munoz, N. M., Leff, A. R., Wilton, D. C., Gelb, M. H., and Cho, W. (1999) J. Biol. Chem. 274, 11881-11888). To determine the mechanism by which hVPLA(2) interacts with cell membranes to induce leukotriene formation, we mutated surface cationic residues and a catalytic residue of hVPLA(2) and measured the interactions of mutants with model membranes, immobilized heparin, and human neutrophils. These studies showed that cationic residues, Lys(7), Lys(11), and Arg(34), constitute a part of the interfacial binding surface of hVPLA(2), which accounts for its moderate preference for anionic membranes. Additionally, hVPLA(2) binds heparin with high affinity and has a well defined heparin-binding site. The site is composed of Arg(100), Lys(101), Lys(107), Arg(108), and Arg(111), and is spatially distinct from its interfacial binding surface. Importantly, the activities of the mutants to hydrolyze cell membrane phospholipids and induce leukotriene biosynthesis, when enzymes were added exogenously to neutrophils, correlated with their activities on phosphatidylcholine membranes but not with their affinities for anionic membranes and heparin. These results indicate that hVPLA(2) acts directly on the outer plasma membranes of neutrophils to release fatty acids and lysophospholipids. Further studies suggest that products of hVPLA(2) hydrolysis trigger the cellular leukotriene production by activating cellular enzymes involved in leukotriene formation. Finally, the temporal and spatial resolution of exogenously added hVPLA(2) and mutants suggests that binding to cell surface heparan sulfate proteoglycans is important for the internalization and clearance of cell surface-bound hVPLA(2).

Roles of ionic residues of the C1 domain in protein kinase C-alpha activation and the origin of phosphatidylserine specificity

On the basis of extensive structure-function studies of protein kinase C-alpha (PKC-alpha), we have proposed an activation mechanism for conventional PKCs in which the C2 domain and the C1 domain interact sequentially with membranes (Medkova, M., and Cho, W. (1999) J. Biol. Chem. 274, 19852-19861). To further elucidate the interactions between the C1 and C2 domains during PKC activation and the origin of phosphatidylserine specificity, we mutated several charged residues in two C1 domains (C1a and C1b) of PKC-alpha. We then measured the membrane binding affinities, activities, and monolayer penetration of these mutants. Results indicate that cationic residues of the C1a domain, most notably Arg(77), interact nonspecifically with anionic phospholipids prior to the membrane penetration of hydrophobic residues. The mutation of a single aspartate (Asp(55)) in the C1a domain to Ala or Lys resulted in dramatically reduced phosphatidylserine specificity in vesicle binding, activity, and monolayer penetration. In particular, D55A showed much higher vesicle affinity, activity, and monolayer penetration power than wild type under nonactivating conditions, i.e. with phosphatidylglycerol and in the absence of Ca(2+), indicating that Asp(55) is involved in the tethering of the C1a domain to another part of PKC-alpha, which keeps it in an inactive conformation at the resting state. Based on these results, we propose a refined model for the activation of conventional PKC, in which phosphatidylserine specifically disrupts the C1a domain tethering by competing with Asp(55), which then leads to membrane penetration and diacylglycerol binding of the C1a domain and PKC activation.

Blockade of eosinophil migration and airway hyperresponsiveness by cPLA2-inhibition

We examined the role of a cytosolic phospholipase A2 (cPLA2) in antigen-induced eosinophil infiltration of airways and in airway hyperresponsiveness to methacholine. Inhibition of cPLA2, or blockade of the platelet-activating factor (PAF) receptor, blocked antigen-induced airway hyperresponsiveness and suppressed eosinophil infiltration. Neither cyclooxygenase nor 5-lipoxygenase inhibition had either effect. We show here that, in antigen-sensitized guinea pigs, cPLA2 inhibition prevents both eosinophilic infiltration and subsequent airway hyperresponsiveness after antigen challenge. We also show that this effect is mediated by first-step hydrolysis of membrane phospholipid into lysophospholipid rather than by prostanoid or leukotriene metabolites of arachidonate.

Mechanism of annexin I-mediated membrane aggregation

It has been proposed that annexin I has two separate interaction sites that are involved in membrane binding and aggregation, respectively. To better understand the mechanism of annexin I-mediated membrane aggregation, we investigated the properties of the inducible secondary interaction site implicated in membrane aggregation. X-ray specular reflectivity measurements showed that the thickness of annexin I layer bound to the phospholipid monolayer was 31 +/- 2 A, indicating that annexin I binds membranes as a protein monomer or monolayer. Surface plasmon resonance measurements of annexin I, V, and mutants, which allowed evaluation of membrane aggregation activity of annexin I separately from its membrane binding, revealed direct correlation between the relative membrane aggregation activity and the relative affinity of the secondary interaction site for the secondary membrane. The secondary binding was driven primarily by hydrophobic interactions, unlike calcium-mediated electrostatic primary membrane binding. Chemical cross-linking of membrane-bound annexin I showed that a significant degree of lateral association of annexin I molecules precedes its membrane aggregation. Taken together, these results support a hypothetical model of annexin I-mediated membrane aggregation, in which a laterally aggregated monolayer of membrane-bound annexin I directly interacts with a secondary membrane via its induced hydrophobic interaction site.

Structure, function, and regulation of group V phospholipase A(2)

The hydrolysis of membrane phospholipid by phospholipase A(2) (PLA(2)) is a key step in the production of inflammatory eicosanoids. Recent cell studies have shown that secretory group V PLA(2) (gVPLA(2)) is involved in agonist-induced eicosanoid biosynthesis in mouse P388D1 cell line, mast cells, and transfected HEK 293 cells. gVPLA(2) is homologous to other group II PLA(2) family members but has distinctive enzymatic properties, including its activity to effectively hydrolyze phosphatidylcholine (PC) vesicles and the outer plasma membrane of mammalian cells. Mutational studies showed that gVPLA(2) has a unique structure that allows effective binding to PC membranes and efficient catalysis of an active-site-bound PC substrate. Thanks to this unique structure and activity, exogenously added gVPLA(2) can induce the eicosanoid biosynthesis in unstimulated inflammatory cells, including human neutrophils and eosinophils, suggesting that it might be able to trigger inflammatory responses under certain physiological conditions. Extensive structure-function and cell studies showed that gVPLA(2) could act directly on the outer plasma membranes of neutrophils and eosinophils. The release of fatty acids and lysophospholipids from the cell surfaces induces the translocation and activation of cytosolic PLA(2) and 5-lipoxygenase, resulting in the leukotriene synthesis. In case of neutrophils, induction of leukotriene B(4) synthesis by gVPLA(2) leads to the phosphorylation of cytosolic PLA(2) by a leukotriene B(4) receptor and MAP kinase-mediated mechanism. Finally, heparan sulfate proteoglycans in neutrophils appear to play a role of internalizing and degrading the cell surface-bound gVPLA(2) to protect the cells from extensive lipolytic damage.

Seroprevalence of porcine respiratory coronavirus in selected Korean pigs

A total of 446 serum samples from 88 herds in Korea were examined for antibody to porcine respiratory coronavirus (PRCV) using blocking enzyme-linked immunosorbent assay (ELISA). All serum samples were collected from 24- to 26-week-old finishing pigs between December 1998 and June 1999. By ELISA, 237 out of 446 sera tested (53.1%) and 54 out of 88 sampled herds (61.3%) were positive against PRCV. Of 446 sera from 88 herd tested, 185 (41.5%) serum samples from 22 (25%) herds were seronegative against PRCV and transmissible gastroenteritis virus infection. Our data suggested that seropositive herds for PRCV are distributed diffusely throughout South Korea.

Dietary L-carnitine improves nitrogen utilization in growing pigs fed low energy, fat-containing diets

Growing pigs (n = 25; 17.8 +/- 0.1 kg) were used to study the effects of L-carnitine and protein intake on nitrogen (N) balance and body composition. Fat-supplemented (40 g soy oil/kg diet), corn-soybean meal basal diets containing low or high protein (136 or 180 g/diet) were formulated so that protein accretion would be limited by metabolizable energy (ME). Each basal diet was supplemented with 0 or 500 mg/kg L-carnitine and fed to pigs for 10 d in a nutrient balance trial. Final body composition was compared with weight and age-matched pigs measured on d 0 to calculate nutrient accretion rates. High protein feeding increased (P < 0.01) average daily gain (ADG) by 34%, as well as nitrogen digestibility (4.4%), retention (5.2%), urinary excretion (29%) and crude protein (CP) accretion (33%). Total-body carnitine accretion rate was 4.5 fold greater and total body carnitine concentration was almost 100% greater than in unsupplemented controls (P < 0.01). Irrespective of protein level, carnitine increased ADG (by 7.3%, P < 0.10) and CP accretion rate (9%, P < 0.10). Congruently, carnitine supplementation improved the efficiency of nitrogen retention (P < 0. 05) and reduced urinary nitrogen excretion (14%, P < 0.10). Carcass fat content also was reduced in carnitine-supplemented pigs (P < 0. 10). Collectively, these data support the hypothesis that carnitine can improve the efficiency of nitrogen utilization in 20-kg pigs fed energy-limited, fat-containing diets. We conclude that endogenous carnitine biosynthesis may be adequate to maintain sufficient tissue levels during growth, but that supplemental dietary carnitine (at 500 mg/kg) may be retained sufficiently so as to alter nutrient partitioning and thus body composition of 20-kg pigs.

The molecular basis of phosphatidylcholine preference of human group-V phospholipase A2

Human group-V phospholipase A(2) (hVPLA(2)) is a secretory phospholipase A(2) (PLA(2)) that is involved in eicosanoid formation in such inflammatory cells as macrophages and mast cells. We showed that hVPLA(2) can bind phosphatidylcholine membranes and hydrolyse phosphatidylcholine molecules much more efficiently than human group-IIa PLA(2), which accounts for its high activity on the outer plasma membrane of mammalian cells. To understand the molecular basis of the high phosphatidylcholine specificity of hVPLA(2), we mutated several residues (Gly-53, Glu-56 and Glu-57) that might be involved in interaction with an active-site-bound phospholipid molecule. Phospholipid head-group specificities of mutants determined using polymerized mixed-liposome substrates indicate that a small glycine residue in position 53 is important for accommodating a bulky choline head group. Also, results indicated that two anionic residues, Glu-56 and Glu-57, favourably interact with cationic head groups of phosphatidylcholine and phosphatidylethanolamine. Together, these steric and electrostatic properties of the active site of hVPLA(2) allow for effective binding and hydrolysis of a bulky cationic choline head group of phosphatidylcholine, which is unique among mammalian secretory PLA(2)s.

Characterization of monoclonal antibodies specific for 14-kDa human group V secretory phospholipase A2 (hVPLA2)

Secretory phospholipase A2 (PLA2) consists of several 14-kDa isoforms with extensive homology, which makes it difficult to identify a specific isoform. In this study, we have developed and characterized monoclonal antibodies (MAbs) directed specifically against human group V sPLA2 (hVPLA2) derived from cultured hybridomas. These hybridomas were produced from the fusion of BALB/c-derived myeloma s/p20-Ag14 and splenocytes from mice immunized with purified recombinant hVPLA2. Three hybridomas secreting MAbs, MCL-3G1, MCL-2A5, and MCL-1B7, were selected and subcloned on the basis of their specificity to recognize hVPLA2 using solid-phase enzyme-linked immunoadsorbent assay (ELISA). The purified MAbs demonstrated a common pattern of immunoreactivity to hVPLA2, but not to human group IIa isoform (hIIaPLA2). Isotype analysis indicates that these hybridomas are of the IgG1 type. Under reducing conditions, MCL-3G1 sensitively detected hVPLA2 and demonstrated no cross-reactivity to either hIIaPLA2 or group IV cytosolic PLA2. Although specific for hVPLA2, a relatively modest signal was recognized with MCL-1B7 and MCL-2A5. These newly developed MAbs allow for determination of tissue distribution and cell-specific functions of hVPLA2.

Roles of aromatic residues in high interfacial activity of Naja naja atra phospholipase A2

Acidic phospholipase A2 (PLA2) from the venom of Chinese cobra (Naja naja atra) has high activity on zwitterionic membranes and contains six aromatic residues, including Tyr-3, Trp-18, Trp-19, Trp-61, Phe-64, and Tyr-110, on its putative interfacial binding surface. To assess the roles of these aromatic residues in the interfacial catalysis of N. n. atra PLA2, we mutated them to Ala and measured the effects on its interfacial catalysis. Enzymatic activities of the mutants toward various vesicle substrates and human neutrophils indicate that all but Trp-18 make significant contributions to interfacial catalysis. Among these aromatic residues, Trp-19, Trp-61, and Phe-64 play the most important roles. Binding affinities of the mutants for phospholipid-coated beads and their monolayer penetration indicate that Trp-19, Trp-61, and Phe-64 are critically involved in interfacial binding of N. n. atra PLA2 and penetrate into the membrane during the interfacial catalysis of N. n. atra PLA2. Further thermodynamic analysis suggests that the side chain of Phe-64 is fully inserted into the hydrophobic core of membrane whereas those of Trp-19 and Trp-61 are located in the membrane-water interface. Together, these results show that all three types of aromatic residues can play important roles in interfacial binding of PLA2 depending on their location and side-chain orientation. They also indicate that these aromatic side chains interact with membranes in distinct modes because of their different intrinsic preference for different parts of membranes.

Structural determinant of the vesicle aggregation activity of annexin I

Some annexins, including annexins I, II, IV, and VII, can promote membrane aggregation. To identify amino acids involved in annexin I-mediated membrane aggregation, we generated truncated mutants of human annexin I lacking various parts of the amino terminus. The in vitro vesicle binding and aggregation activities of these mutants indicated that both the amino-terminal region of annexin I spanning residues 26-29 and the carboxy-terminal core are involved in membrane aggregation. This notion was further supported by the finding that a chimera composed of residues 24-35 of annexin I and the core of annexin V has vesicle aggregation activity that is significantly higher than that of annexin V but lower than that of annexin I. Further site-specific mutations in the amino-terminal region of annexin I indicated that Lys-26 and Lys-29 are essential for its membrane aggregation activity. The comparison of tryptic digest patterns of free and vesicle-bound wild type and K29E mutant suggests that a primary role of Lys-26 and Lys-29 is to induce and stabilize an active conformation of annexin I for vesicle aggregation.

Cytosolic phospholipase A2 activation is essential for beta 1 and beta 2 integrin-dependent adhesion of human eosinophils

We examined the role of cytosolic phospholipase A2 (cPLA2) during human eosinophil adherence to ICAM-1- or VCAM-1-coated plates. IL-5-stimulated eosinophils adhered to ICAM-1 through the beta 2 integrin CD11b/CD18, while nonstimulated eosinophils did not. By contrast, nonstimulated eosinophils adhered to VCAM-1 through the beta 1-integrin VLA-4/CD29. Both IL-5-induced adhesion to ICAM-1 and spontaneous adhesion to VCAM-1 corresponded temporally to cPLA2 phosphorylation, which accompanied enhanced catalytic activity of cPLA2. The structurally unrelated cPLA2 inhibitors, arachidonyl trifluoromethylketone and surfactin, significantly inhibited eosinophil adhesion to ICAM-1 and VCAM-1 in a concentration-dependent manner. Inhibition of secretory PLA2, 5-lipoxygenase, or cyclooxygenase did not affect eosinophil adhesion. Addition of arachidonic acid to eosinophils after cPLA2 inhibition with arachidonyl trifluoromethylketone or surfactin did not reverse the blockade of adhesion to ICAM-1 or VCAM-1. However, CV-6209, a receptor-specific antagonist of platelet-activating factor, inhibited all integrin-mediated adhesion. The activated conformation of CD11b as identified by the mAb, CBRM1/5, as well as quantitative surface CD11b expression were up-regulated after IL-5 stimulation. However, cPLA2 inhibition neither prevented CBRM1/5 expression nor blocked surface Mac-1 up-regulation caused by IL-5. Our data suggest that cPLA2 activation and its catalytic product platelet-activating factor play an essential role in regulating beta 1 and beta 2 integrin-dependent adhesion of eosinophils. This blockade occurs even in the presence of up-regulated eosinophil surface integrin.

Interfacial binding of secreted phospholipases A(2): more than electrostatics and a major role for tryptophan

Secreted phospholipases A(2) have similar catalytic sites, but vastly different interfacial binding surfaces that modulate their binding affinity for different kinds of phospholipid vesicles by several orders of magnitude. The structure/function principles that dictate both the differential interfacial binding and the physiological function of these enzymes are beginning to be unraveled.

Interplay of C1 and C2 domains of protein kinase C-alpha in its membrane binding and activation

The regulatory domain of conventional protein kinase C (PKC) contains two membrane-targeting modules, the C2 domain that is responsible for Ca2+-dependent membrane binding of protein, and the C1 domain composed of two cysteine-rich zinc fingers (C1a and C1b) that bind diacylglycerols and phorbol esters. To understand the individual roles and the interplay of the C1 and C2 domains in the membrane binding and activation of PKC, we functionally expressed isolated C1 and C2 domains of PKC-alpha and measured their vesicle binding and monolayer penetration. Results indicate that the C2 domain of PKC-alpha is responsible for the initial Ca2+- and phosphatidylserine-dependent electrostatic membrane binding of PKC-alpha, whereas the C1 domain is involved in subsequent membrane penetration and diacylglycerol binding, which eventually lead to enzyme activation. To determine the roles of individual zinc fingers in the C1 domain, we also mutated hydrophobic residues in the C1a (Trp58 and Phe60) and C1b (Tyr123 and Leu125) domains of the native PKC-alpha molecule and measured the effects of mutations on vesicle binding, enzyme activity and monolayer penetration. Results show that the hydrophobic residues in the C1a domain are essential for the membrane penetration and activation of PKC-alpha, whereas those in the C1b domain are not directly involved in these processes. Based on these results in conjunction with our previous structure-function studies of the C2 domain (Medkova, M., and Cho, W. (1998) J. Biol. Chem. 273, 17544-17552), we propose a mechanism for the in vitro membrane binding and activation of conventional PKC that accounts for the temporal and spatial sequences of PKC activation.

A structural determinant of the unique interfacial binding mode of bovine pancreatic phospholipase A2

The catalytic steps of the phospholipase A2 (PLA2)-catalyzed hydrolysis of phospholipids are preceded by interfacial binding. Among various pancreatic PLA2s, bovine pancreatic PLA2 (bpPLA2) has a unique interfacial binding mode in which Lys-56 plays an important role in its binding to anionic lipid surfaces. To identify the structural determinant of this unique interfacial binding mode of bpPLA2, we systematically mutated bpPLA2 and measured the effects of mutations on its interfacial binding and activity. First, different cationic clusters were generated in the amino-terminal alpha-helix by the N6R, G7K, and N6R/G7K mutations. These mutations enhanced the binding of bpPLA2 to anionic liposomes up to 15-fold. For these mutants, however, the K56E mutation still caused a large drop in interfacial affinity for and activity toward anionic liposomes, indicating that the generation of a cationic patch in the amino-terminal alpha-helix of bpPLA2 did not change its interfacial binding mode. Second, residues 62-66 that form a part of the pancreatic loop were deleted. For this deletion mutant (Delta62-66), which was as active as wild-type toward anionic liposomes, the K56E and K116E mutations (Delta62-66/K56E and Delta62-66/K116E) did not have significant effects on interfacial affinity. In contrast, the K10E mutation showed a much larger decrease in interfacial affinity (10-fold), indicating the deletion of residues 62-66 caused a major change in the interfacial binding mode. Finally, hydrophobic residues in positions 63 and 65 were replaced by bulkier ones (V63F and V63F/V65L) to pinpoint the structural determinant of the interfacial binding mode of bpPLA2. The effects of K10E and K56E mutations on the interfacial affinity and activity of these mutants showed that Val-63 and Val-65 of bpPLA2 are the structural determinant of its unique interfacial binding mode and that relatively conservative substitutions at these positions result in large changes in the interfacial binding mode among mammalian pancreatic PLA2s. Taken together, this study reveals how minor structural differences among homologous PLA2s can lead to distinct interfacial binding behaviors.

Differential interfacial and substrate binding modes of mammalian pancreatic phospholipases A2: a comparison among human, bovine, and porcine enzymes

To identify the residues essential for interfacial binding and substrate binding of human pancreatic phospholipase A2 (hpPLA2), several ionic residues in the putative interfacial binding surface (R6E, K7E, K10E, and K116E) and substrate binding site (D53K and K56E) were mutated. Interfacial affinity of these mutants was measured using anionic polymerized liposomes, and their enzymatic activity was measured using various substrates including phospholipid monomers, zwitterionic and anionic micelles, and anionic polymerized mixed liposomes. Similar mutations (R6E, K10E, K56E, and K116E) were made to porcine pancreatic phospholipase A2 (ppPLA2), and the properties of mutants were measured by the same methods. Results indicate that hpPLA2 and ppPLA2 have similar interfacial binding mechanisms in which cationic residues in the amino terminus and Lys-116 in the carboxy terminus are involved in binding to anionic lipid surfaces. Small but definite differences between the two enzymes were observed in overall interfacial affinity and activity and the effects of the mutations on interfacial enzyme activity. The interfacial binding of hpPLA2 and ppPLA2 is distinct from that of bovine pancreatic phospholipase A2 in that Lys-56 is involved in the interfacial binding of the latter enzyme. The unique phospholipid headgroup specificity of hpPLA2 derives from the presence of Asp-53 in the substrate binding site. This residue appears to participate in stabilizing electrostatic interactions with the cationic ethanolamine headgroup, hence the phosphatidylethanolamine preference of hpPLA2. Taken together, these studies reveal the similarities and the differences in the mechanisms by which mammalian pancreatic phospholipases A2 interact with lipid aggregates and perform interfacial catalysis.

Roles of Trp31 in high membrane binding and proinflammatory activity of human group V phospholipase A2

Group V phospholipase A2 is a recently discovered secretory phospholipase A2 (PLA2) that has been shown to be involved in eicosanoid formation in inflammatory cells, such as macrophages and mast cells. We have demonstrated that human group V PLA2 (hsPLA2-V) can bind phosphatidylcholine (PC) membranes and hydrolyze PC substrates much more efficiently than human group IIa PLA2, which makes it better suited for acting on the outer plasma membrane (Han, S.-K., Yoon, E. T., and Cho, W. (1998) Biochem. J. 331, 353-357). In this study, we demonstrate that exogenous hsPLA2-V has much greater activity than does group IIa PLA2 to release fatty acids from various mammalian cells and to elicit leukotriene B4 formation from human neutrophils. To understand the molecular basis of these activities, we mutated two surface tryptophans of hsPLA2-V to alanine (W31A and W79A) and measured the effects of these mutations on the kinetic activity toward various substrates, on the binding affinity for vesicles and phospholipid-coated beads, on the penetration into phospholipid monolayers, and on the activity to release fatty acids and elicit eicosanoid formation from various mammalian cells. These studies show that the relatively high ability of hsPLA2-V to induce cellular eicosanoid formation derives from its high affinity for PC membranes and that Trp31 on its putative interfacial binding surface plays an important role in its binding to PC vesicles and to the outer plasma membrane.

Mechanisms by which elevated intracellular calcium induces S49 cell membranes to become susceptible to the action of secretory phospholipase A2

Exposure of S49 lymphoma cells to exogenous group IIA or V secretory phospholipase A2 (sPLA2) caused an initial release of fatty acid followed by resistance to further hydrolysis by the enzyme. This refractoriness was overcome by exposing cells to palmitoyl lysolecithin. This effect was specific in terms of lysophospholipid structure. Induction of membrane susceptibility by lysolecithin involved an increase in cytosolic calcium and was duplicated by incubating the cells with calcium ionophores such as ionomycin. Lysolecithin also activated cytosolic phospholipase A2 (cPLA2). Inhibition of this enzyme attenuated the ability of lysolecithin (but not ionomycin) to induce susceptibility to sPLA2. Lysolecithin or ionomycin caused concurrent hydrolysis of both phosphatidylethanolamine and phosphatidylcholine implying that transbilayer movement of phosphatidylethanolamine occurred upon exposure to these agents but that susceptibility is not simply due to exposure of a preferred substrate (i.e. phosphatidylethanolamine) to the enzyme. Microvesicles were apparently released from the cells upon addition of lysolecithin or ionomycin. Both these vesicles and the remnant cell membranes were susceptible to sPLA2. Together these data suggest that lysolecithin induces susceptibility through both cPLA2-dependent and -independent pathways. Whereas elevated cytosolic calcium was required for both pathways, it was sufficient only for the cPLA2-independent pathway. This cPLA2-independent pathway involved changes in cell membrane structure associated with transbilayer phospholipid migration and microvesicle release.

A structure-function study of the C2 domain of cytosolic phospholipase A2. Identification of essential calcium ligands and hydrophobic membrane binding residues

The C2 domain of cytosolic phospholipase A2 (cPLA2) is involved in the Ca2+-dependent membrane binding of this protein. To identify protein residues in the C2 domain of cPLA2 essential for its Ca2+ and membrane binding, we selectively mutated Ca2+ ligands and putative membrane-binding residues of cPLA2 and measured the effects of mutations on its enzyme activity, membrane binding affinity, and monolayer penetration. The mutations of five Ca2+ ligands (D40N, D43N, N65A, D93N, N95A) show differential effects on the membrane binding and activation of cPLA2, indicating that two calcium ions bound to the C2 domain have differential roles. The mutations of hydrophobic residues (F35A, M38A, L39A, Y96A, Y97A, M98A) in the calcium binding loops show that the membrane binding of cPLA2 is largely driven by hydrophobic interactions resulting from the penetration of these residues into the hydrophobic core of the membrane. Leu39 and Val97 are fully inserted into the membrane, whereas Phe35 and Tyr96 are partially inserted. Finally, the mutations of four cationic residues in a beta-strand (R57E/K58E/R59E/R61E) have modest and negligible effects on the binding of cPLA2 to zwitterionic and anionic membranes, respectively, indicating that they are not directly involved in membrane binding. In conjunction with our previous study on the C2 domain of protein kinase C-alpha (Medkova, M., and Cho, W. (1998) J. Biol. Chem. 273, 17544-17552), these results demonstrate that C2 domains are not only a membrane docking unit but also a module that triggers membrane penetration of protein and that individual Ca2+ ions bound to the calcium binding loops play differential roles in the membrane binding and activation of their parent proteins.