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J P Segrest

Publications and source records attributed to J P Segrest.

At least 55 records · Page 3Linked to original sources
PubMed1995

Identification and cholesterol quantification of low density lipoprotein subclasses in young adults by VAP-II methodology.

Low density lipoprotein (LDL) particles are heterogeneous in size, density, and chemical composition; small, dense LDL may be more atherogenic than large, buoyant LDL. We have developed a rapid microscale method called LDL VAP-II (Vertical Auto Profile-II) for quantification of cholesterol in LDL subclasses. The method is based upon a short (1 h) single vertical spin density-gradient ultracentrifugation and on-line VAP-II analyzer. LDL VAP-II is rapid and reproducible. Using this method five LDL subclasses, designated as LDL-1 (most buoyant) through LDL-5 (most dense), have been identified in a population consisting of 195 medical students (ages, 22-29 years). The Rf (relative position of the major LDL peak in the density gradient; the higher the Rf value, the lower the peak density) was significantly positively correlated with cholesterol levels of high density lipoprotein (HDL) (r = 0.594), HDL3 (0.350) and HDL2 (0.625), and significantly negatively correlated with triglycerides (TG) (-0.355) and cholesterol levels of very low density lipoprotein (VLDL) (-0.386) and intermediate density lipoprotein (IDL) (-0.432). These results are consistent with those obtained by other investigators. The Rf value was significantly correlated with peak particle diameter as determined by non-denaturing gradient gel electrophoresis (r = 0.859). In a forward stepwise multivariate analysis comparing Rf with sex, VLDL, LDL, Lp[a], IDL, HDL3, HDL2, and triglyceride, only HDL2 remained in the model.

Adult↗
PubMed1994

Binding of apolipoprotein A-I model peptides to lipid bilayers. Measurement of binding isotherms and peptide-lipid headgroup interactions.

Amphiphatic alpha-helices are the lipid-binding motif in many apolipoproteins. Two model peptides, namely Asp-Trp-Leu-Lys-Ala-Phe-Tyr-Asp-Lys-Val-Ala-Glu-Lys-Leu-Lys-Glu-Ala-Phe (18A) and Lys-Trp-Leu-Asp-Ala-Phe-Tyr-Lys-Asp-Val-Ala-Lys-Glu-Leu-Glu-Lys-Ala- Phe (18R), have been synthesized previously to mimic the structural and functional properties of apolipoprotein A-1. Here a quantitative thermodynamic analysis of the binding process of 18A and 18R to neutral and negatively charged lipid membranes is provided. Peptide 18A has a higher lipid affinity than 18R, and both peptides bind better to mixed 1-palmitoyl-2-oleoyl-3-sn-glycero-phosphocholine-1- palmitoyl-2-oleoyl-3-sn-glycero-phosphoglycerol (POPC/POPG) bilayers than to pure POPC bilayers. At lipid-to-peptide ratios > 100, the binding of 18A and 18R to phospholipid bilayers can be described by an apparent surface partition equilibrium with binding constants in the range of 40-900 M-1. At high peptide concentrations, the membrane affinity of 18A and 18R increases dramatically. NMR studies provide evidence that peptide-peptide interactions make additional contributions to the binding energy. A cooperative binding model is developed to describe the binding process over the whole concentration range. The cooperativity parameter sigma is identical for 18A and 18R yielding a peptide-peptide interaction energy of about -2.4 kcal/mol. The free energy of membrane insertion is about -6.5 kcal/mol for 18A and -5.5 kcal/mol for 18R. The binding reaction is driven by the hydrophobic surface energy which is partially balanced by the loss in translational and rotational degrees of freedom. A molecular analysis of the free energy of binding predicts a 40-60% insertion of the peptides into the hydrophobic membrane environment. Deuterium and phosphorus solid state NMR were used to monitor the influence of 18A and 18R on the long range and short range order of the phospholipids. The spectra are characteristic of fluid-like lipid bilayers and provide no evidence for the formation of discoidal particles. However, both peptides change the conformation of the phosphocholine dipoles, moving the N+ end of the latter toward the water phase. The rotation of the -P-N+ dipoles is due to the interaction of the phospholipids with the positive charges on 18A and 18R, with 18A being more effective than 18R. For 18R the NMR data predict a pK shift and a partial charge neutralization of the carboxylate groups located at the edge of the polar/nonpolar interface.

Amino Acid Sequence↗
PubMed1994

The influence of apolipoprotein structure on the efflux of cellular free cholesterol to high density lipoprotein.

The influence of apolipoprotein conformation on the ability of high density lipoprotein (HDL) to remove cellular free cholesterol (FC) has not been studied in detail. To address the effects of amphipathic alpha-helix structure on cellular FC efflux, three class A helical peptides and apolipoprotein (apo) AI were complexed to dimyristoyl phosphatidylcholine (DMPC) to make discoidal complexes that were used as acceptors of cell cholesterol. The peptides consisted of an 18-amino acid, amphipathic, alpha-helical peptide with the sequence DWLKAFYDKVAEKLKEAF (18A), a dimer of 18A covalently linked by a proline residue (37pA), and acetyl-18A-amide (Ac-18A-NH2) that has a higher alpha-helix content than the unblocked 18A molecule. The three peptides strongly mimic the lipid-binding characteristics of the amphipathic segments of apolipoproteins and form discoidal complexes with DMPC that are similar in diameter (11-12 nm) to those formed by human apoAI when reconstituted at a 2.5:1 (w:w) phospholipid to protein ratio. The abilities of these complexes to remove radiolabeled FC were compared in experiments using cultured mouse L-cell fibroblasts; efflux of FC from both the plasma membrane and the lysosomal pools was examined. For each of the acceptors, the removal of cholesterol from the plasma membrane and lysosomal pools was equally efficient. All four discoidal complexes were equally efficient cell membrane FC acceptors when compared at saturating acceptor concentrations of > 200 micrograms of DMPC/ml of medium. However, at the same lipid concentration, protein-free DMPC small unilamellar vesicles (SUV) were significantly less efficient. The initial rates of FC removal from cells at saturating concentrations of acceptor particles (Vmax) were 12, 10, 10, and 11% per h, respectively, for the complexes containing either 18A, Ac-18A-NH2, 37pA, or apoAI, but only 1% cellular FC per h for the DMPC SUV. The 10-fold higher Vmax for the apoprotein/peptide-containing acceptors was likely due to a reversible interaction of apoprotein or peptide with the plasma membrane that changed the lipid packing characteristics in such a way as to increase the rate of FC desorption from the cell surface. This interaction required amphipathic alpha-helical segments, but it was not affected by the length, number, or lipid-binding affinity of the helices. Furthermore, the efflux efficiency was not dependent on the amino acid sequence of the helical segments which suggests that this interaction is not mediated by a specific cell surface binding site.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1994

Interactions of synthetic peptide analogs of the class A amphipathic helix with lipids. Evidence for the snorkel hypothesis.

Class A amphipathic helixes present in exchangeable plasma apolipoproteins are characterized by the location of positively charged amino acid residues at the non-polar-polar interface and negatively charged amino acid residues at the center of the polar face. The objectives of the present study were: (i) to investigate the role of hydrocarbon side chain length of the interfacial positively charged amino acid residues in the lipid affinity of class A amphipathic helixes, and (ii) to investigate the importance of the nature of interfacial charge in the lipid affinity of class A amphipathic helixes. Toward this end, lipid interactions of the following two analogs of the class A amphipathic helix, Ac-18A-NH2 (acetyl-Asp-Trp-Leu-Lys-Ala-Phe-Tyr- Asp-Lys-Val-Ala-Glu-Lys-Leu-Lys-Glu-Ala-Phe-NH2), and Ac-18A(Lys > Haa)-NH2 (acetyl-Asp-Trp-Leu-Haa-Ala-Phe-Tyr-Asp-Haa-Val-Ala-Glu-Haa-Leu-Haa-Glu- Ala-Phe-NH2) (Haa = homoaminoalanine), were studied. The side chain of Haa has two CH2 groups less than that of lysine. The lipid affinities of these two peptide analogs were compared with that of Ac-18R-NH2, an analog of Ac-18A-NH2 with positions of the charged amino acid residues reversed. The techniques used in these studies were circular dichroism, fluorescence spectroscopy, right-angle light scattering measurements, and differential scanning calorimetry. The results of these studies indicated the following rank order of lipid affinity: Ac-18A-NH2 > Ac-18A(Lys > Haa)-NH2 > Ac-18R-NH2. These results are in agreement with the "snorkel" model proposed earlier to explain the higher lipid affinity of class A amphipathic helixes (Segrest, J. P., Loof, H. D., Dohlman, J. G., Brouillette, C. G., and Anantharamaiah, G. M. (1990) Proteins Struct. Funct. Genetics 8, 103-117). In addition, it was observed from the differential scanning calorimetry studies that Ac-18A-NH2 and Ac-18A(Lys > Haa)-NH2 interact more strongly than Ac-18R-NH2 with negatively charged dimyristoyl phosphatidylglycerol. The weaker interaction of Ac-18R-NH2 with dimyristoyl phosphatidylglycerol is suggested to be due to electrostatic repulsion between the negatively charged lipid and the interfacial negative charges of the peptide.

Amino Acid Sequence↗
PubMed1994

apoB-100 has a pentapartite structure composed of three amphipathic alpha-helical domains alternating with two amphipathic beta-strand domains. Detection by the computer program LOCATE.

Due to the great length of apolipoprotein (apo) B-100, the localization of lipid-associating domains in this protein has been difficult. To address this question, we developed a computer program called Locate that searches amino acid sequences to identify potential amphipathic alpha-helixes and beta-strands by using sets of rules for helix and strand termination. A series of model chimeric protein test datasets were created by tandem linking of amino acid sequences of multiple proteins containing four different secondary structural motifs: motif A (exchangeable plasma apolipoproteins); motif G (globular alpha-helical proteins); motif C (coiled-coil alpha-helical proteins); and motif B (beta pleated-sheet proteins). These four test datasets, as well as randomly scrambled sequences of each dataset, were analyzed by Locate using increasingly stringent parameters. Using intermediately stringent parameters under which significant numbers of amphipathic helixes were found only in the unscrambled motif A, two dense clusters of putative lipid-associating amphipathic helixes were located precisely in the middle and at the C-terminal end of apoB-100 (a sparse cluster of class G* helixes is located at the N-terminus). The dense clusters are located between residues 2103 through 2560 and 4061 through 4338 and have densities of 2.4 and 2.2 amphipathic helixes per 100 residues, respectively; under these conditions, motif A has a density of 1.4 amphipathic helixes per 100 residues. These two domains correspond closely to the two major apoB-100 lipid-associated domains at residues 2100 through 2700 and 4100 through 4500 using the principle of releasability of tryptic peptides from trypsin-treated intact low-density lipoprotein. The classes of amphipathic helixes identified within these two putative lipid-associating domains are considerably more diverse than those found in the exchangeable plasma apolipoproteins. Interestingly, apoB-48 terminates at the N-terminal edge of the middle cluster. By using a similar strategy for analysis of amphipathic beta-strands, we discovered that the two gap regions between the three amphipathic helix clusters are highly enriched in putative amphipathic beta-strands, while the three amphipathic helical domains are essentially devoid of this putative lipid-associating motif. We propose, therefore, that apoB-100 has a pentapartite structure, NH2-alpha 1-beta 1-alpha 2-beta 2-alpha 3-COOH, with alpha 1 representing a globular domain.

Algorithms↗
PubMed1994

HDL and apolipoprotein A-I protect erythrocytes against the generation of procoagulant activity.

The appearance of anionic lipids on the extracellular surface of cells is required for the formation of the procoagulant complex that leads to the activation of prothrombin. Procoagulant activity would be expected to be inhibited by substances that stabilize the membrane structure and hence inhibit the transbilayer diffusion of phosphatidylserine from the cytoplasmic to the extracellular surface of the plasma membrane. The generation of procoagulant activity in human erythrocytes by A23187 and Ca2+ is inhibited by apolipoprotein A-I, its amphipathic peptide analogues, and high-density lipoprotein (HDL). These agents do not inhibit the Ca2+ loading of erythrocytes by A23187, nor do they inhibit the activation of prothrombin once the cells have been incubated at 37 degrees C with A23187 and Ca2+. Transbilayer diffusion of fluorescently labeled phosphatidylserine is inhibited by apolipoprotein A-I. These findings indicate that class A amphipathic helixes as well as lipoprotein particles and liposomes inhibit the transbilayer diffusion of phospholipids and procoagulant activity. This activity may contribute to the protective role of HDL against arteriosclerosis and thrombosis.

Amino Acid Sequence↗
PubMed1994

Liposome-like particles isolated from human atherosclerotic plaques are structurally and compositionally similar to surface remnants of triglyceride-rich lipoproteins.

Recent studies have demonstrated the presence of unesterified cholesterol-rich, liposome-like vesicles in the extracellular space of atherosclerotic lesions in humans and animals. Liposome-like vesicles accumulate in the subendothelial space in rabbits within 2 weeks of initiation of cholesterol feeding, well before foam cells appear. These observations suggest that extracellular liposome-like vesicles may play a pivotal role in atherogenesis. The origin of these particles is unknown. We report a combination of in vivo and in vitro experiments that suggest a novel origin for these liposome-like vesicles. We demonstrate that the liposome-like particles isolated from postmortem human atherosclerotic plaques are rich in intact apolipoprotein (apo) A-I, C apolipoproteins, and sphingomyelin. We show that the in vivo derived particles are virtually identical, structurally and compositionally, to liposome-like lipolytic surface remnants of triglyceride (TG)-rich lipoproteins produced during in vitro lipolysis of hypertriglyceridemic serum. In vitro lipolysis of isolated very-low-density lipoprotein has shown that the lipolytic surface remnants remain attached to the core remnants in the absence of high-density lipoprotein (HDL), dissociate to form liposome-like vesicles in the presence of low levels of HDL, and are assimilated into HDL to form larger HDL particles in the presence of excess HDL. Thus, the in vitro produced, liposome-like particles represent a complex of lipolytic surface remnants of TG-rich lipoproteins and apo A-I derived from HDL. Two possible origins have been suggested for the extracellular liposome-like vesicles in atherosclerotic plaques: (1) modified, aggregated, and/or degraded LDL particles entrapped in an intimal matrix and (2) intracellular lipid products of arterial wall cells. Neither possibility directly explains the presence of A-I and C apolipoproteins and excess sphingomyelin that we observe. We propose as an alternate explanation that the in vivo liposome-like particles are lipolytic surface remnants of TG-rich lipoproteins. We further suggest that these remnants are produced in the intimal space by undefined processes and/or are transcytosed into the intima from the plasma compartment as a product of normal lipolysis gone awry. We conjecture that one role of HDL may be to assimilate the highly atherogenic liposome-like particles in a (1) "mop-up" fashion to remove them from the artery wall and/or (2) preventive fashion in the plasma compartment to prevent their transcytosis into the artery wall. The suggestion that elevated concentrations of surface remnants act as a "sink" for apo A-I can also account for the well-established but poorly understood link between hypertriglyceridemia and low HDL.

Animals↗
PubMed1994

Synthetic amphipathic helical peptides that mimic apolipoprotein A-I in clearing cellular cholesterol.

Clearance of excess cholesterol from cells by HDL is facilitated by the interaction of HDL apolipoproteins with cell-surface binding sites or receptors, a process that may be important in preventing atherosclerosis. In this study, synthetic peptides containing 18-mer amphipathic helices of the class found in HDL apolipoproteins (class A) were tested for their abilities to remove cholesterol and phospholipid from cultured sterol-laden fibroblasts and macrophages and to interact with cell-surface HDL binding sites. Lipid-free peptides containing two identical tandem repeats of class A amphipathic helices promoted cholesterol and phospholipid efflux from cells and depleted cellular cholesterol accessible for esterification by acyl CoA/cholesterol acyltransferase, similar to what was observed for purified apolipoprotein A-I. Peptide-mediated removal of plasma membrane cholesterol and depletion of acyl CoA/cholesterol acyltransferase-accessible cholesterol appeared to occur by separate mechanisms, as the latter process was less dependent on extracellular phospholipid. The dimeric amphipathic helical peptides also competed for high-affinity HDL binding sites on cholesterol-loaded fibroblasts and displayed saturable high-affinity binding to the cell surface. In contrast, peptides with a single helix had little or no ability to remove cellular cholesterol and phospholipid, or to interact with HDL binding sites, suggesting that cooperativity between two or more helical repeats is required for these activities. Thus, synthetic peptides comprising dimers of a structural motif common to exchangeable apolipoproteins can mimic apolipoprotein A-I in both binding to putative cell-surface receptors and clearing cholesterol from cells.

Amino Acid Sequence↗
PubMed1994

Mixing rates can markedly affect the kinetics of peptide-induced leakage from liposomes.

Assays on vesicle aqueous content leakage are widely used in the study of peptide-lipid interactions. We found this assay to be affected by the mode of mixing vesicle and peptide solutions. This effect can lead to artifactual conclusions regarding the lytic activity of peptides. We demonstrate that the source of this artifact is that fast (millisecond range) peptide-membrane association creates a nonhomogeneous distribution which exists sufficiently long after peptide addition to markedly alter the course of leakage. Mixing problems can be overcome by using a stopped flow apparatus. It can also be diminished by switching to injecting a small volume of vesicle suspension into a large volume of peptide solution. Mixing rates are rarely considered in literature reports of peptide effects on liposomes. The same artifacts can also take place in a number of other assays of the activity of membrane active peptides on liposomes and thus their consideration is of general importance.

Artifacts↗
PubMed1994

Pathogenesis of atherosclerosis.

Two recent developments provide strong support for the role of plasma lipoproteins in plaque formation: plaque stabilization due to rapid removal of cholesterol from macrophage-foam cells has been suggested to explain the rapid cessation of clinical coronary artery disease events after aggressive lipoprotein-modifying therapy; and transgenic mice studies using overexpression and gene knockout of apolipoproteins A-I and E suggest that remnant lipoprotein particles are atherogenic and that apolipoprotein A-I (high-density lipoprotein) can clearly inhibit atherosclerosis development. Two of the more exciting areas of vascular-wall biology at this time are the possibility that endothelial dysfunction may be assessed by measurement of circulating factors (such as atherosclerosis-associated endothelial leukocyte adhesion molecule), and studies of the role of fibrin-like peptides in atherogenesis and coronary artery disease risk assessment.

Arteries↗
PubMed1994

Quantification of cholesterol in all lipoprotein classes by the VAP-II method.

We have developed a high resolution microvolume Vertical Auto Profile (VAP) method for the simultaneous measurement of cholesterol in all lipoprotein classes, including lipoprotein[a] (Lp[a]) and intermediate density lipoprotein (IDL). This method, designated as VAP-II, uses a non-segmented continuous flow (controlled-dispersion flow) analyzer for the enzymatic analysis of cholesterol in lipoprotein classes separated by a short spin (47 min) single vertical ultracentrifugation. Cholesterol concentrations of high (HDL), low (LDL), very low (VLDL), and intermediate (IDL) density lipoproteins, as well as Lp[a], are determined by decomposing the spectrophotometric absorbance curve, obtained from the continuous analysis of the centrifuged sample, into its components using software developed in this laboratory. Analysis by VAP-II is rapid and sensitive (as little as 40 microliters plasma is required per assay). The resolution of lipoprotein peaks is considerably enhanced in the present analyzer compared to the previous analyzer (VAP-I, which used the Technicon AutoAnalyzer); improvement is especially noticeable for Lp[a] and IDL. Total and lipoprotein cholesterol values obtained by VAP-II correlated well with the values obtained by Northwest Lipid Research Laboratories (NWLRL). VAP-II Lp[a] cholesterol values also correlated well with the Lp[a] mass values obtained by an immunoassay technique performed at NWLRL (r = 0.907). The reproducibility and accuracy of the method are within the requirements of the CDC-NHLBI (Centers for Disease Control-National Heart, Lung, and Blood Institute) Lipid Standardization Program.

Blood Chemical Analysis↗
PubMed1993

Cytosolic domain of the human immunodeficiency virus envelope glycoproteins binds to calmodulin and inhibits calmodulin-regulated proteins.

Calmodulin (CaM), the major intracellular receptor for calcium, is involved in regulation of diverse cellular functions. Positively charged amphipathic helical segments have been identified as an important structural motif in the recognition of CaM by different CaM-activated enzymes and peptides. The carboxyl-terminal domain of the envelope glycoproteins of human and simian immunodeficiency viruses (HIV-1, HIV-2, and SIV) contain regions that can fold into amphipathic helical segments, which closely resemble the amphipathic segments found in CaM-activated enzymes. We show here that synthetic peptide analogs corresponding to the two putative amphipathic helical regions of HIV-1/WMJ gp160 bind to CaM with high affinity (Kd 31-41 nM) in the presence of calcium. They also bind CaM in the absence of calcium, although with much lower affinity. The peptides inhibit CaM-regulated activation of bovine brain phosphodiesterase in vitro. The peptides also inhibit mitogen-induced lymphocyte activation, a property shared by CaM antagonists. Purified HIV-1 gp160 binds to CaM, while gp120, which lacks the putative amphipathic helical segments, does not bind CaM. In HIV-infected cells, the putative CaM-binding regions of gp160 are located intracellularly and may therefore interact with the cytosolic CaM. We postulate that CaM binding by HIV envelope proteins is likely to exert diverse modulatory effects, and the mechanism for HIV-induced cytotoxicity may involve, in part, inhibition of CaM-regulated cellular functions.

Amino Acid Sequence↗
PubMed1993

Reciprocal effects of apolipoprotein and lytic peptide analogs on membranes. Cross-sectional molecular shapes of amphipathic alpha helixes control membrane stability.

Apolipoprotein (class A) amphipathic helixes are postulated to act as detergents by virtue of their cross-section being wedge-shaped. Using computer analysis of naturally occurring class A and lytic (class L) amphipathic helixes, we designed two archetypical model peptides. Analogs of these two peptides, incorporating substitutions or modifications of interfacial or basic residues, had the following effects. Class A peptides stabilized bilayer structure, reduced leakage from large unilamellar vesicles and erythrocytes, and inhibited lysis induced by class L peptides. Class L peptides destabilized bilayer structure in model membranes and increased binding of class A peptides to erythrocytes. The ability of class L analogs to lyse membranes and induce inverted lipid phases was reduced by either decreasing the bulk of an interfacial residue, increasing the angle subtended by the polar face, or increasing the bulk of the basic residues. The ability of the class A analog to stabilize bilayer structure and inhibit erythrocyte lysis by class L peptides was enhanced by methylating the Lys residues. These results can be explained by a model that we term the reciprocal wedge hypothesis. By analogy to the reciprocal effects of phospholipid shapes on membrane structure, we propose that the wedge shape of class A helixes stabilizes membrane bilayers, whereas the inverted wedge shape of class L helixes destabilizes membrane bilayers, and, thus, one class will neutralize the effect of the other class on membranes.

Amino Acid Sequence↗
PubMed1993

Effect of end group blockage on the properties of a class A amphipathic helical peptide.

In a recent classification of biologically active amphipathic alpha-helixes, the lipid-associating domains in exchangeable plasma apolipoproteins have been classified as class A amphipathic helixes (Segrest, J.P., De Loof, H., Dohlman, J.G., Brouillette, C.G., Anantharamaiah, G.M. Proteins 8:103-117, 1990). A model peptide analog with the sequence, Asp Trp Leu Lys Ala Phe Tyr Asp Lys Val Ala Glu Lys Leu Lys Glu Ala Phe (18A), possesses the characteristics of a class A amphipathic helix. The addition of an acetyl group at the alpha-amino terminus and an amide at the alpha-carboxyl terminus, to obtain Ac-18A-NH2, produces large increases in helicity for the peptide both in solution and when associated with lipid (for 18A vs Ac-18A-NH2, from 6 to 38% helix in buffer and from 49 to 92% helix when bound to dimyristoyl phosphatidylcholine in discoidal complexes). Blocking of the end-groups of 18A stabilizes the alpha-helix in the presence of lipid by approximately 1.3 kcal/mol. There is also an increase in the self-association of the blocked peptide in aqueous solution. The free energy of binding to the PC-water interface is increased only by about 3% (from -8.0 kcal/mol for 18A to -8.3 kcal/mol for Ac-18A-NH2). The Ac-18A-NH2 has a much greater potency in raising the bilayer to hexagonal phase transition temperature of dipalmitoleoyl phosphatidylethanolamine than does 18A. In this regard Ac-18A-NH2 more closely resembles the behavior of the apolipoprotein A-I, which is the major protein component of high-density lipoprotein and a potent inhibitor of lipid hexagonal phase formation. The activation of the plasma enzyme lecithin: cholesterol acyltransferase by the Ac-18A-NH2 peptide is greater than the 18A analog and comparable to that observed with the apo A-I. In the case of Ac-18A-NH2, the higher activating potency may be due, at least in part, to the ability of the peptide to micellize egg PC vesicles.

Apolipoprotein A-I↗
PubMed1993

Thyroid function and other clinical chemistry parameters in subjects eating iodine-enriched eggs.

Iodine-enriched (IE) eggs are produced by chickens fed a diet containing kelp. These eggs, which contain an average of 711 micrograms iodine/egg, have been reported to reduce plasma cholesterol in humans and laboratory animals. A modified form of these eggs is under consideration for marketing in the United States. 104 hyperlipidaemic subjects were placed on a low-fat diet for 12 wk. Between wk 4 and 12, approximately half of the subjects were randomized to a dietary control group (n = 53) or a group who ingested one IE egg/day in addition to this diet (n = 51). Some subjects in both groups continued in the study for an additional 4-8 wk. No significant adverse clinical effects were observed or reported, with the exception of one subject who reported an allergic-like reaction soon after beginning egg ingestion. All clinical chemistry values remained within normal limits, and comparisons between the egg group and controls were not significant. Three subjects (two in the egg group and one in the control group) had elevated thyroid stimulating hormone levels during the experimental period. All thyroid function tests remained within normal limits in the remaining subjects. Thus, ingestion of one IE egg of the type used in our study appears to be relatively safe and devoid of clinically significant, short-term adverse effects in healthy individuals.

Animals↗
PubMed1993

A mathematically defined motif for the radial distribution of charged residues on apolipoprotein amphipathic alpha helixes.

Multiple amphipathic alpha-helical candidate domains have been identified in exchangeable apolipoproteins by sequence analysis and indirect experimental evidence. The distribution of charged residues can differ within and between these apolipoproteins. Segrest et al. (Segrest, J. P., H. DeLoof, J. G. Dohlman, C. G. Brouillette, and G. M. Anantharamaiah. 1990. Proteins. 8:103-117.) argued that these differences are correlated with lipid affinity. A mathematically defined motif for the particular charge distribution associated with high lipid affinity (class A) is proposed. Primary sequence data from protein segments proposed previously to have an amphipathic alpha-helical structure are scanned. Counting formulas are presented for determining the conditional probability that the match between an observed charge distribution and the proposed motif would occur by chance. Because the preselected helical segments are short (the modal length is 22) and the motif definition imposes multiple constraints on the acceptable distributions, the computer-based algorithm is quite feasible computationally. 19 of the 20 segments previously assigned to class A match the motif sufficiently well (the remaining one is borderline), while very few others "erroneously" pass the screening test. These results confirm the original assignments of the candidate domains and, thus, support the hypothesis that there is a distinguishable subset of helixes having high lipid affinity. This counting approach is applicable to a growing subset of protein sequence analysis problems in which the segment lengths are short and the motif is complex.

Apolipoproteins↗