Biomedical subjects

K Oikawa

Publications and source records attributed to K Oikawa.

At least 73 records · Page 4Linked to original sources

PubMed1995

[Free radical generation in electron transport system of mitochondria after cold preservation in UW solution].

UNLABELLED: In the liver transplantation one of the causes of primary graft nonfunction is likely associated with lipid peroxidation at reperfusion after cold preservation. In this study, we investigated whether free radicals produced in mitochondrial electron transport system would result in lipid peroxidation after cold preservation in UW solution. MATERIALS AND METHODS: Under anesthesia, the liver of male Wistar rat was flushed via the portal vein with cold Ringer lactate, and then placed in 4 degrees C UW solution for 24 hr. After cold preservation, we examined mitochondrial respiratory control ratio (RCR), free radicals (O2-) from mitochondrial electron transport system by MCLA induced chemiluminescence, and lipid peroxidation by chemiluminescence (CL) after reoxygenation. RESULTS: RCR gradually decreased up to 24 hr preservation. O2- generation from mitochondrial electron transport system was not recognized at any length of the time after cold preservation up to 24 hr. At 6 hr, CL values were slightly higher than those of the control, but significantly decreased at 24 hr. CONCLUSION: O2(-)-generated in electron transport system of mitochondria did not increase with cold preservation up to 24 hr, therefore, the radical from mitochondria did not cause a lipid peroxidation at reperfusion injury.

Adenosine↗

PubMed1995

Bacterial expression and site-directed mutagenesis of a functional recombinant apolipoprotein.

To facilitate structure-function studies of Manduca sexta apolipophorin III (apoLp-III), its nucleotide coding sequence was cloned from a fat body cDNA library by in vitro DNA amplification. The amplification product was cloned in the pET expression vector and introduced into E. coli. After induction, cultures were screened for apoLp-III protein production by immunoblotting with anti-apoLp-III serum. Data obtained indicated the presence of apoLp-III in both cell lysates and media of cell cultures harboring the apoLp-III-pET construct but not in cells containing the parent vector. The protein was isolated from the cell-free supernatant of cultures grown in minimal media 4 h after induction. Verification that the recombinant protein produced was indeed apoLp-III was obtained by electrospray mass spectrometric analysis. Circular dichroism (CD) spectroscopy of the isolated recombinant protein revealed a characteristic content of alpha-helical secondary structure with a further induction of helix upon addition of 50% trifluoroethanol. In urea denaturation studies, monitored by CD, evidence was obtained that recombinant and natural apoLp-III possess indistinguishable thermodynamic properties. In addition, lipid binding assays revealed that recombinant apoLp-III formed stable complexes with phospholipids and was capable of associating with lipoprotein surfaces. Examination of the fluorescence properties of recombinant apoLp-III revealed the presence of a noncovalently associated fluorescent contaminant that was effectively removed by reverse phase HPLC.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

The properties of specific binding site of 125I-radioiodinated myotoxin a, a novel Ca++ releasing agent, in skeletal muscle sarcoplasmic reticulum.

It was found that myotoxin a (MYTX), which is isolated from prairie rattlesnakes (Crotalus viridis viridis), is a powerful Ca++ releaser in the heavy fraction of sarcoplasmic reticulum (HSR). 125I-labeled MYTX (125I-MYTX), which has high Ca(++)-releasing ability, was successfully prepared. It specifically bound to a single class of binding sites in HSR with a KD of 0.4 microM and Bmax of 6 nmol/mg of protein. 125I-MYTX binding was markedly inhibited by Na+ and K+, whereas it was little affected by Ca++ and Mg++. The binding activity was markedly decreased by spermine, a blocker of Ca++ releasing channels, and was not affected by the other modulators of Ca++ release such as caffeine, procaine or ruthenium red. Spermine decreased the binding in a concentration-dependent manner with the IC50 value of 20 microM. Scatchard analysis of 125I-MYTX binding indicated that the Bmax value was decreased by spermine, although the KD value was not changed, which indicates a noncompetitive mode of inhibition. 125I-MYTX did not bind to the purified ryanodine receptor. Ca++ electrode experiments indicated that MYTX induced Ca++ release from HSR at doses of 0.1 microM or more; this was abolished by spermine. The maximal response to MYTX (10 microM) was further increased by caffeine (10 mM) in 45Ca++ release, which probably indicates that the effects of MYTX and caffeine are synergistic in Ca(++)-releasing action. These results suggest that MYTX binds to an important regulatory protein of Ca++ release, which is not the ryanodine receptor.

Amino Acid Sequence↗

PubMed1994

Structural and binding characteristics of the carboxyl terminal fragment of apolipophorin III from Manduca sexta.

The molecular basis of the interaction of apolipophorin III (apoLp-III), an exchangeable apolipoprotein from hemolymph of the sphinx moth. Manduca sexta, with lipoprotein surfaces and phospholipids was studied by investigating the structural and binding properties of the C-terminal fragment of the native protein. A 4K peptide, corresponding to the terminal helical segment of the native protein, was generated by cyanogen bromide treatment, purified by gel filtration and reverse-phase HPLC, and characterized by N-terminal sequencing and amino acid and mass spectrometric analysis. Circular dichroism (CD) spectroscopy of the peptide in buffer indicated a predominantly unstructured state while addition of trifluoroethanol (TFE), a helix-inducing agent, resulted in an alpha-helical structure. Sedimentation equilibrium studies revealed that the 4K peptide was monomeric in buffer. The 4K peptide assumed an alpha-helical conformation in the presence of sodium dodecyl sulfate (SDS) and lysolecithin, but was unstructured in the presence of dimyristoylphosphatidylcholine, either when added to preformed vesicles or upon cosonication, indicating an ability to bind to detergent micelles but not to phospholipid bilayers. Unlike native apoLp-III, the 4K peptide did not confer protection against turbidity development to human low density lipoprotein upon incubation with phospholipase C, indicating an inability to interact with the surface of lipoproteins. Upon interaction with SDS micelles, both the 4K peptide and apoLp-III were resistant to urea-induced denaturation when compared to free apoLp-III, as evaluated by CD spectroscopy. The structural stability conferred upon interaction with detergents was similar for both the peptide and the native protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1994

Properties of human plasma lipid transfer protein in aqueous solution and at interfaces.

Human plasma lipid transfer protein (cholesteryl ester transfer protein) has been characterized for its solution and surface properties. The protein is monomeric in aqueous solution up to 0.62 g/L (11.7 microM) as demonstrated by sedimentation equilibrium. It binds to the surface of a lipid microemulsion having an average diameter of 26 nm made from triolein and egg yolk phosphatidylcholine, with an estimated dissociation constant 1.2 x 10(-8) M, and the maximum saturation binding level is 8 protein molecules per particle regardless of the presence of apolipoprotein A-I. Circular dichroism measurement indicated that the protein in solution is predominantly in the beta-sheet/beta-turn conformation with some alpha-helix, and this profile does not undergo drastic change by its binding to the lipid surface. The analysis of the behavior of the protein in its monomolecular layer at the air-buffer interface indicated that it is also monomeric at the interface. LTP molecules occupied the same area per amino acid as other apolipoproteins in the monolayer but had a higher collapse pressure of its monolayer (18 dyn/cm), and the protein stayed at the interface even after the overcompressing monolayer far beyond the collapsing pressure up to 40 dyn/cm.

Apolipoprotein A-I↗

PubMed1994

Factors affecting the stability and conformation of Locusta migratoria apolipophorin III.

Apolipophorin III (apoLp-III) from the migratory locust, Locusta migratoria, represents the only full-length apolipoprotein whose three-dimensional structure has been solved. In the present study, spectroscopic methods have been employed to investigate the effects of deglycosylation (via endoglycosidase F treatment) and complexation with lipid on the stability and conformation of this protein. Addition of isolated lipid-free apoLp-III to sonicated vesicles of dimyristoylphosphatidylcholine (DMPC) resulted in the formation of relatively uniform disklike complexes with an average Strokes diameter of 13.5 nm. Flotation equilibrium experiments conducted in the analytical ultracentrifuge revealed a particle molecular mass of 588 500 Da. Chemical cross-linking and compositional analysis of apoLp-III.DMPC complexes indicated five apoLp-III molecules per disk and an overall DMPC:apoLp-III molar ratio of 122:1. Circular dichroism (CD) spectra of apoLp-III samples suggested a loss of alpha-helical structure upon deglycosylation, while complexation with DMPC did not significantly alter the helix content (estimated to be > 75%). Fluorescence spectroscopy revealed that the apoLp-III tryptophan fluorescence emission maximum was blue-shifted from 347 to 332 and 321 nm upon deglycosylation and complexation with DMPC, respectively. In quenching experiments with native apoLp-III, tryptophan residues were shielded from the positively charged quencher, CsCl. Increased exposure to KI, CsCl, and acrylamide was observed upon deglycosylation, whereas complexation with DMPC yielded lower Ksv values for KI and acrylamide and an increased value for CsCl versus native lipid-free apoLp-III. In guanidine hydrochloride denaturation studies monitored by CD or fluorescence, native, lipid-free apoLp-III displayed a denaturation midpoint of 0.60 M, and delta GDH2O = 5.37 kcal/mol was calculated.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylamide↗

PubMed1994

Ca2+, Mg2+, and troponin I inhibitory peptide binding to a Phe-154 to Trp mutant of chicken skeletal muscle troponin C.

The effects of Ca2+, Mg2+, and troponin I (TnI) inhibitory peptide (Ip) binding on the spectral properties of a Phe-154 to Trp mutant (F154W) of chicken recombinant troponin C (rTnC) have been examined. Residue 154 is positioned in the final flanking helix H of metal binding site IV. Since there are no other Tyr or Trp residues in the protein, spectral properties can be unambiguously assigned. No significant differences in the far UV CD spectra of rTnC and F154W were observed in either the absence or presence of Ca2+. When reconstituted into whole Tn the ATPase specific activities (+/- Ca2+) of the troponin-tropomyosin-actomyosin subfragment 1 system were the same for both proteins. A 2-fold reduction in Ca2+ affinity of C domain sites III/IV but not of N domain sites I/II in isolated F154W is explicable in terms of the environment of residue 154 in the relatively disordered apo-C domain and its buried position in the known ordered 2Ca2+ crystal structure. Filling of sites III/IV by divalent cations was accompanied by a number of spectral changes which were different for Ca2+ and Mg2+. Binding of Ip peptides (residues 96-116 and 104-115(116)) elicited fluorescence emission spectral alterations in the presence of Ca2+. These were not observed in its absence nor in the presence of Mg2+ even though binding occurs under these conditions. Since Ca2+ affinity to C domain but not to N domain sites was increased by Ip at the low concentrations of protein and Ip tested, Ip binding appears to be stronger with C domain.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1994

Binding of insect apolipophorin III to dimyristoylphosphatidylcholine vesicles. Evidence for a conformational change.

Apolipophorin-III (apoLp-III), a hemolymph protein of Manduca sexta, can reversibly associate with the surface of lipoprotein particles. In order to examine the lipid-associated form of apoLp-III, the present studies investigate the structure and properties of apoLp-III complexes with dimyristoylphosphatidylcholine (DMPC). Association of apoLp-III with DMPC vesicles results in the formation of uniform discs with an average diameter and width of 18.5 +/- 2.0 nm and 4.8 +/- 0.8 nm, respectively, as determined by electron microscopy. ApoLp-III.DMPC complexes analyzed by pore-limiting native gradient PAGE demonstrated that a single major species of complex was formed within a wide range of lipid to protein molar ratios (DMPC:apoLp-III; 13:1 to 360:1). Flotation equilibrium experiments, conducted in an analytical ultracentrifuge, confirmed that only one species of apoLp-III.DMPC complex was formed at an initial lipid to protein molar ratio of 67:1, with an apparent molecular mass of 642,000. Complexes cross-linked with dimethyl suberimidate indicate that there are a maximum of 6 apoLp-III molecules per disc. Circular dichroism experiments revealed that apoLp-III becomes essentially completely alpha-helical on formation of apoLp-III.DMPC complexes. Compared to apoLp-III in the lipid-free state, apoLp-III.DMPC complexes were relatively resistant to denaturation by guanidine HCl, displaying denaturation transitions with midpoints at 2.2 and 3.7 M guanidine HCl, respectively. The fluorescence excitation and emission spectra of apoLp-III.DMPC complexes demonstrate a large enhancement of tyrosine fluorescence as compared to the lipid-free state, suggesting that a conformational change occurs when apoLp-III associates with a lipid surface. Denaturation of apoLp-III in the complex by guanidine HCl resulted in a tyrosine fluorescence level similar to that of lipid-free apoLp-III in the presence of guanidine HCl. The tyrosine-induced fluorescence of the complex was quenched with both Cs+ (Kq = 0.573 M-1) and KI (Kq = 0.376 M-1). The results presented in this study indicate that the conformation of apoLp-III is stabilized when complexed with phospholipids and suggest that tyrosine fluorescence provides a sensitive method to detect M. sexta apoLp-III interaction with lipid surfaces.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Ascorbic acid radical, superoxide, and hydroxyl radical are detected in reperfusion injury of rat liver using electron spin resonance spectroscopy.

Using electron spin resonance (ESR) spectroscopy, we examined whether reactive oxygen intermediates (ROIs) are produced after reperfusion of isolated, perfused rat livers subjected to global ischemia (10, 30, 60, and 90 min of ischemia). A few drops of effluent (200 microliters) flowed from reperfused liver was mixed immediately with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO, final concentration 1 M), and ESR measurements were then performed. Immediately after reperfusion, a small amount of ascorbic acid radical and DMPO-OOH, which was formed by the reaction of superoxide with DMPO, was detected. The amount of ascorbic acid radical peaked immediately after reperfusion, but became hardly detectable at 6 min after reperfusion, irrespective of the period of ischemia. Six minutes after reperfusion, not only DMPO-OOH but also DMPO-OH, which was formed by the reaction of hydroxyl radical with DMPO, was detected. Thereafter, DMPO-OOH and DMPO-OH gradually declined and became hardly detectable at 40 min after reperfusion. In accordance with the duration of ischemia, the concentrations of DMPO-OOH and DMPO-OH were highest after 60 min of ischemia, and then after 30, 90, and 10 min of ischemia in decreasing order. These results directly demonstrate that the production of ROIs occurs at an early stage of reperfusion in ischemic liver and that the amount of ROI production is closely related to the duration of ischemia.

Animals↗

PubMed1994

[Home chemotherapy for peritoneal carcinomatosis].

Nineteen patients diagnosed with peritoneal carcinomatosis were treated by in-home chemotherapy over a period of four years from August, 1990 to July, 1994. Primary diagnoses of the four male and 15 female patients included 12 cases gastric cancer (four males, eight females), five cases of ovarian cancer, one case (female) of appendicular cancer, and one case (female) of breast cancer. In addition to oral administration of UFT-E and 5'-DFUR, chemotherapy included weekly intravenous injection of a massive dose of 5-FU (1,000 mg/m2), subselective intraaortic infusion and intraperitoneal infusion using a reservoir. These methods were used individually and in combination. The drugs used included 5-FU, CBDCA, CPA, THP, and EPIR. Subselective intraaortic infusion was performed by low dose continuous infusion using the Baxter infusor multiday type. Six gastric cancer patients lived normally for over one year, while four died in less than a year. All ovarian and appendicular cancer patients were CR, the breast cancer patient was PR. Ten patients continued working at their jobs while receiving at home chemotherapy treatments. Diuretics were used to alleviats ascites. Although there were no side effects on digestive organs, 5-FU and CBDCA were mixed with 100 mg hydrocortisone in the infusor to improve cachexia, and promote appetite and activity. Bone marrow suppression was very slight at these dosages, and weekly checkups were adequate. The at-home rate (number of days at home/entire period since onset) of all patients was 78%.

Adult↗

PubMed1993

Physical properties of apolipoprotein A-I from the chicken, Gallus domesticus.

The amphipathic alpha-helices of exchangeable apolipoproteins (apo) function to simultaneously facilitate interaction with lipid surfaces and the aqueous environment. In contrast to mammalian apoA-I's, which self-associate in the absence of lipid, chicken apoA-I, which shares 66% sequence homology with human apoA-I, exists as a monomeric protein when dissociated from high-density lipoprotein (HDL). Sedimentation equilibrium studies conducted in the analytical ultracentrifuge yielded a weight-average molecular weight of 28,170. Corresponding sedimentation velocity and diffusion experiments gave rise to s0(20,w) = 2.23 S and D0(20,w) = 6.39 x 10(-7) cm2/s. A translational frictional ratio (f/fmin) of 1.18 and an axial ratio of 4.0 were also determined from this data. The Stokes radius (Rs,sed = 2.80 nm) and translational frictional ratio were subsequently used to calculate estimated molecular dimensions of 25.2 x 100.8 A for chicken apoA-I. Circular dichroism (CD) studies revealed a highly alpha-helical structure predicted to be 74% by Provencher-Glöckner analysis. Denaturation studies performed on lipid-free apoA-I and monitored by CD revealed a midpoint of denaturation of 0.64 M guanidine hydrochloride. From plots of delta G(app) versus guanidine hydrochloride concentration, a delta GDH2O of 1.86 kcal/mol was determined. In other studies, a midpoint of temperature-induced denaturation for apoA-I of 57 degrees C was obtained. The effect of solvent pH on the secondary structure content of apoA-I revealed a significant loss of alpha-helix below pH 4.0 and above pH 10, suggesting that lipid-free apoA-I may by partially stabilized by the formation of intra- or interhelix salt bridges between oppositely charged amino acid side chains.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Purification, characterization, and conformational analysis of rabbit plasma lipid transfer protein.

A procedure for rapid isolation of lipid transfer protein (LTP) from commercially available rabbit plasma is described. Use of protease inhibitors was important for obtaining intact, stable LTP. After lipoproteins were precipitated from the plasma by dextran sulfate, column chromatographies through Butyl-Toyopearl 650M, CM-Toyopearl 650M, and Butyl-Toyopearl 650M were employed. Overall purification from plasma was (3830 +/- 710)-fold with a yield of 3-5%. The isolated LTP migrated as a single band during sodium dodecyl sulfate-polyacrylamide gel electrophoresis with M(r) = 74K and had an NH2-terminal amino acid sequence and amino acid composition closely matching those predicted by its cDNA. This band was recognized by immunoblotting with an anti-human LTP monoclonal antibody, TP2. Gel permeation chromatography revealed that LTP behaved as a globular protein of M(r) = 83K. Isoelectric focusing of the isolated LTP demonstrated a ladder of bands with pI's of 5.7-5.9. The specific activity of rabbit LTP was similar to that of human LTP. Monoclonal antibody TP2, that blocked human plasma LTP activity almost completely, only partially inhibited purified rabbit LTP, and rabbit plasma LTP activity to a similar extent. By a centrifugation binding assay, rabbit LTP was shown to predominantly associate with lipid microemulsion in its presence. Circular dichroism spectroscopy indicated a high content of beta structure, and Provencher and Glöckner analysis gave estimated fractional values of 0.30, 0.39, 0.12, and 0.19 for alpha-helix, beta-sheet, beta-turn, and remainder content, respectively. Upon lipid binding, the helical content did not change drastically, although there was some disordering of beta structure.

Amino Acid Sequence↗

PubMed1993

Conformational, thermodynamic, and stability properties of Manduca sexta apolipophorin III.

Apolipophorin III (apoLp-III) is a major protein in hemolymph of adult Manduca sexta. Although it normally exists in a lipid-free state, during sustained flight, apoLp-III functions as an apolipoprotein, reversibly associating with the surface of lipoprotein particles. In an effort to gain a fuller understanding of this dual existence, we have investigated its solution properties using spectroscopic methods. The UV absorption spectrum of apoLp-III is distinctive owing to the absence of tryptophan and the presence of a single tyrosine residue. Circular dichroism experiments revealed an enhancement of apoLp-III alpha-helical content when spectra were obtained in 50% trifluoroethanol versus aqueous buffer. The helical content in buffer was unaffected by protein concentration, suggesting that apoLp-III exists in solution as a monomeric species. At pH values > 10 and < 4, there was a marked loss of helical content. Increasing the temperature of apoLp-III solutions also caused a loss of secondary structure, with a temperature-induced denaturation midpoint of 52 degrees C. Upon recooling of heat-denatured apoLp-III, approximately 95% of the secondary structure was restored. In guanidine HCl denaturation studies monitored by CD, a 50% transition midpoint of 0.355 M was determined, corresponding to a delta GDH2O of 1.29 kcal/mol. Fluorescence studies indicated that guanidine HCl induced an enhancement of tyrosine fluorescence emission at 300 nm when excited at 277 nm. In native apoLp-III, we propose that tyrosine fluorescence is quenched to a large extent due to a hydrophobic stacking interaction of its side chain with that of a neighboring phenylalanine residue. delta GDH2O was determined from the fluorescence data to be 2.1 kcal/mol, with a transition midpoint occurring at 0.25 M guanidine HCl. The lower concentration of guanidine HCl required to induce half-maximal tyrosine fluorescence enhancement versus the transition midpoint detected by CD may be a reflection of the fact that this residue is located near the COOH-terminal end of the protein and as such may be more susceptible to denaturation. The results presented indicate that apoLp-III assumes a relatively labile conformation in solution that appears to be partially stabilized by side chain charge-charge interactions within predicted alpha-helical segments.

Animals↗

PubMed1993

Structural properties of the myelin-associated glycoprotein ectodomain.

Myelin-associated glycoprotein (MAG) has been proposed to mediate adhesive interactions during myelin development. We have used the baculovirus expression system to produce a truncated form of this molecule [soluble extracellular domain of MAG (sMAG)] consisting of the complete extracellular ectodomain. Spectroscopic studies indicate a high beta-sheet content, consistent with the prediction of Ig-like structure. Hydrodynamic studies indicate an asymmetric monomer, with a Stokes radius of 4.1-4.6 nm, a sedimentation coefficient of 3.6S, and a frictional ratio of approximately 1.6. We postulate that the outer two Ig-like domains form a unit that folds back over the rest of the molecule. Fluorescence quenching studies indicate that sMAG interacts with divalent cations and may have a functional lectin domain.

Amino Acids↗

PubMed1992

Construction and characterization of a spectral probe mutant of troponin C: application to analyses of mutants with increased Ca2+ affinity.

A spectral probe mutant (F29W) of chicken skeletal muscle troponin C (TnC) has been prepared in which Phe-29 has been substituted by Trp. Residue 29 is at the COOH-terminal end of the A helix immediately adjacent to the Ca2+ binding loop of site I (residues 30-41) of the regulatory N domain. Since this protein is naturally devoid of Tyr and Trp, spectral features can be assigned unambiguously to the single Trp. The fluorescent quantum yield at 336 nm is increased almost 3-fold in going from the Ca(2+)-free state to the 4Ca2+ state with no change in the wavelength of maximum emission. Comparisons of the Ca2+ titration curves of the change in far-UV CD and fluorescence emission indicated that the latter was associated only with the binding of 2Ca2+ to the regulatory sites I and II. No change in fluorescence was detected by titration with Mg2+. The Ca(2+)-induced transitions of both the N and C domains were highly cooperative. Addition of Ca2+ also produced a red shift in the UV absorbance spectrum and a reduction in positive ellipticity as monitored by near-UV CD measurements. The fluorescent properties of F29W were applied to an investigation of five double mutants: F29W/V45T, F29W/M46Q, F29W/M48A, F29W/L49T, and F29W/M82Q. Ca2+ titration of their fluorescent emissions indicated in each case an increased Ca2+ affinity of their N domains. The magnitude of these changes and the decreased cooperativity observed between Ca2+ binding sites I and II for some of the mutants are discussed in terms of the environment of the mutated residues in the 2Ca2+ and modeled 4Ca2+ states.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Human apolipoprotein A-I liberated from high-density lipoprotein without denaturation.

Apolipoprotein A-I (apoA-I) was liberated from human high-density lipoprotein (HDL) without exposure to organic solvents or chaotropic salts by the action of isolated insect hemolymph lipid transfer particle (LTP). LTP-catalyzed lipid redistribution results in transformation of HDL into larger, less dense particles accompanied by an overall decrease in HDL particle surface area:core volume ratio, giving rise to an excess of amphiphilic surface components. Preferential dissociation of apolipoprotein versus phospholipid and unesterified cholesterol from the particle surface results in apolipoprotein recovery in the bottom fraction following ultracentrifugation at a density = 1.23 g/mL. ApoA-I was then isolated from other contaminating HDL apolipoproteins by incubation with additional HDL in the absence of LTP, whereupon apolipoprotein A-II and the C apolipoproteins reassociate with the HDL surface by displacement of apoA-I. After a second density gradient ultracentrifugation, electrophoretically pure apoA-I was obtained. Sedimentation equilibrium experiments revealed that apoA-I isolated via this method exhibits a tendency to self-associate in an aqueous solution while its circular dichroism spectrum was indicative of a significant amount of alpha-helix. Both measurements are consistent with that observed on material prepared by denaturation/renaturation. The ability of apoA-I to activate lecithin:cholesterol acyltransferase was found to be similar to that of apoA-I isolated by conventional methods. The present results illustrate that LTP-mediated alteration in lipoprotein particle surface area leads to dissociation of substantial amounts of surface active apoprotein components, thus providing the opportunity to isolate apoA-I without the denaturation/renaturation steps common to all previous isolation procedures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Effect of particle lipid content on the structure of insect lipophorins.

Four distinct subspecies of the major insect lipoprotein, lipophorin, that range in overall lipid content from 20 to 51% of the particle mass, were isolated from the hemolymph or oocytes of the tobacco hornworm, Manduca sexta. Examination of these subspecies by electron microscopy revealed distinctive morphologies. Adult high density lipophorin (HDLp-A) was found to be an approximately spherical particle with a diameter of 15 +/- 1 nm, while HDLp-Wanderer 1 (W1), was more rectangular in shape and had a distinct cleft extending into the particle at one end. In the case of HDLp-Wanderer 2 (W2) the cleft was deeper and wider than that in HDLp-W1. In egg very high density lipophorin (VHDLp-E) the cleft was increased in size to the extent that the particle had an overall crescent-like conformation. Circular dichroism spectroscopy of the three lipophorin subspecies that contain only apolipophorin I and II revealed that only minor differences in the global protein secondary structure occur as the particle lipid content is decreased. The VHDLp-E apolipoproteins are an exception in that, while having the same alpha-helix content as HDLp-W1 and HDLp-W2, they contain less beta-structure and correspondingly more random coil. Limited digestion of the apolipoprotein components of the lipophorin subspecies with trypsin revealed that as the lipid content of the particles decreases the susceptibility of the apolipoprotein to proteolytic degradation increases. Likewise, tryptophan fluorescence quenching experiments demonstrated that the relative exposure of lipophorin apolipoprotein tryptophan residues also increases as the particle lipid content decreases.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Heme peptide as a model substance for halogenomethane activation and heme modification.

Octa-heme peptide (CHP) obtained from Candida krusei cytochrome c was tested for suicidal activation of halogenomethanes. Under anaerobic conditions, CHP was kept in the reduced state in the presence of NADPH and NADPH-cytochrome P-450 reductase. Addition of CBrCl3 to the reduced CHP caused spectral changes such as rapid disappearance of alpha and beta bands and gradual decrease in the gamma-peak height, accompanied by oxidation of NADPH. Heme content of the reaction mixture, determined as pyridine hemochrome, also decreased NADPH dependently. CCl4 was less effective than CBrCl3, while CHCl3 had almost no effect. N-tert-butyl-alpha-phenylnitrone (PBN) suppressed the CBrCl3-induced heme damage, and resulted in the formation of radical adduct .PBN-CCl3 as evidenced by ESR spectroscopy. Radical formation was also observed with CCl4. The CHP damage induced by CBrCl3 was also accompanied by the release of Br- about 11-12-times molar excess of CHP, whereas the release of CHCl3 was about 20% that of Br-.FD-MS assay of the product of CHP reaction suggested that 10 trichloromethyl radicals bonded with CHP. Thus, CBrCl3 undergoes single-electron reduction in the presence of reduced CHP to trichloromethyl radicals, which covalently bind to CHP molecules. Heme peptide may be a useful tool in the study of mechanisms involved in the destruction of cytochrome P-450 by halogenomethanes.

Amino Acid Sequence↗