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Biomedical subjects

A Jonas

Publications and source records attributed to A Jonas.

At least 109 records · Page 6Linked to original sources
PubMed1985

Effects of amino group modification in discoidal apolipoprotein A-I-egg phosphatidylcholine-cholesterol complexes on their reactions with lecithin:cholesterol acyltransferase.

Discoidal complexes of human apolipoprotein A-I-egg phosphatidylcholine-cholesterol were prepared by the sodium cholate dialysis procedure and were reacted to varying extents with the amino group reagents citraconic anhydride, diketene, and formaldehyde in the presence of sodium borohydride. Modification of positive lysine residues with negative or neutral groups (citraconic anhydride and diketene, respectively) resulted, for extensively reacted complexes (90%), in structural alterations and in a marked decrease in reactivity with purified human lecithin:cholesterol acyltransferase. The structural and kinetic effects were partially reversible by removal of the modifying groups or by increased ionic strength. Similar extents of modification (84%) with retention of positive charge and introduction of two methyl groups (reductive methylation) had no effect on the structure or the reactivity of the complexes. These results, together with kinetic data at variable complex concentrations or at variable temperatures, indicate that specific lysine residues of apolipoprotein A-I are not involved in the lecithin:cholesterol acyltransferase activation process; instead, charge interactions and structural changes are responsible for the observed decrease in activating capacity. In terms of kinetic parameters, intrinsic K*m values and probably enzyme-substrate particle dissociation constants are affected, but the activation energies remain the same upon chemical modification.

Apolipoprotein A-I↗
PubMed1985

Kinetics of lecithin-cholesterol acyltransferase reaction with discoidal complexes of apolipoprotein A-I.phosphatidylcholine.ether phospholipid.cholesterol.

Discoidal substrates for purified human lecithin-cholesterol acyltransferase were prepared with human apolipoprotein A-I, cholesterol, and egg phosphatidylcholine (PC) or dipalmitoyl PC, including dihexadecyl PC in various proportions as an enzymatically inert dilutor of the interfacial PC substrate. All the complexes, prepared by the sodium cholate dialysis method, were found to be very similar in size, lipid/apolipoprotein stoichiometry, and apolipoprotein spectral properties to the small discoidal complexes without any dihexadecyl PC, described previously (Jonas, A., and Matz, C.E. (1982) Biochemistry 21, 6867-6872; Jonas, A., and McHugh, H. T. (1984) Biochim. Biophys. Acta 794, 361-372). The kinetic results presented in the form of double reciprocal plots of initial velocity against bulk PC or interfacial PC concentration were linear according to the Verger et al. kinetic model (Verger, R., Mieras, M. C. E., and de Haas, G. H. (1973) J. Biol. Chem. 248, 4023-4034) for an initial enzyme binding via an interfacial recognition site followed by interfacial substrate binding and catalysis, in the presence of a competitive interfacial inhibitor. The results indicate, furthermore, that the affinity of the active site for the substrate and inhibitor is quite similar.

Apolipoprotein A-I↗
PubMed1985

Assessment of intestinal and cardiorespiratory function in children with congenital heart disease on high-caloric formulas.

Fourteen infants with congenital heart disease were investigated for failure to thrive. Assessment of intestinal function revealed minor absorptive abnormalities (mild steatorrhea in three patients, bile salt loss in four patients), delayed gastric emptying, and abnormal triglyceride loading tests. Low caloric intake (88.3 +/- 19.3 kcal/kg/day) seemed the main reason for failure to gain weight. Weight accession and cardiorespiratory rates were monitored daily during voluntary intake, a high-caloric diet by mouth, and nasogastric tube feeding. Providing 169 +/- 29 kcal/kg/day by tube resulted in weight gain with mild and transient elevation of respiratory rate at the end of the meal and increased heart rate 90 min after the meal. This regimen is a metabolically inexpensive and efficient method of supporting weight gain in children with congenital heart disease.

Age Factors↗
PubMed1985

Ia-like antigens in the small intestinal mucosa of normal and celiac children.

The small-intestinal mucosa of normal children and of celiac patients was studied using the Class II DP (SB) Ia-like monoclonal antibody ILR-1 and an immunoperoxidase technique. Positive staining of the Golgi region of the epithelial cells of villi and crypts, and of the brush border of villous epithelium, was seen in the histologically normal mucosa. In active celiac disease with "flat" mucosa, the surface epithelium showed poor staining, but the crypt epithelium stained strongly in the Golgi region. We suggest that the Ia-like antigens are a product of the epithelial cells themselves, arising most likely in the Golgi apparatus, and that this staining pattern is altered in active celiac disease.

Celiac Disease↗
PubMed1984

Reaction of lecithin: cholesterol acyltransferase with micellar substrates. Effect of particle sizes.

Micellar, discoidal complexes were prepared from L-alpha-dipalmitoylphosphatidylcholine (DPPC) or egg phosphatidylcholine (egg-PC), cholesterol, and human apolipoprotein A-I by the cholate dialysis method. Reaction mixtures containing from 70:7:1 to 500:50:1, PC/cholesterol/apolipoprotein A-I (mol/mol) were fractionated by gel-filtration into various complex fractions. The isolated DPPC complexes ranged in size from 103 to 380 A in diameter, and in composition from 70:7:1 to 470:45:1, PC/cholesterol/apolipoprotein A-I (mol/mol), respectively. In contrast, the isolated egg-PC complexes only ranged in size from 105 to 214 A in diameter, and in composition from 65:5:1 to 153:17:1, PC/cholesterol/apolipoprotein A-I (mol/mol), respectively. Measurements of fluorescence wavelength maxima and fluorescence polarization of tryptophan residues of apolipoprotein A-I, in both series of complexes, revealed uniform spectral properties for all the egg-PC containing complexes. The DPPC complexes, on the other hand, had maxima in the fluorescence parameters for complexes with diameters around 200 A. When reacted with purified human lecithin:cholesterol acyltransferase, either at constant apolipoprotein A-I or at constant lipid concentration, all egg-PC complexes had very similar reaction rates, but the DPPC complex series exhibited major differences in reactivity. Minima in reaction rates occurred for DPPC complexes around 200 A in diameter, and optimal rates were observed with the small discoidal complexes (110 A in diameter). These reaction rates correlate well with the apolipoprotein A-I fluorescence properties and indicate that the apolipoprotein structure, reflected at the interface with phosphatidylcholine, may be the most important factor in determining complex reactivity with lecithin:cholesterol acyltransferase.

Apolipoprotein A-I↗
PubMed1984

Discoidal complexes of A and C apolipoproteins with lipids and their reactions with lecithin: cholesterol acyltransferase.

Micellar, discoidal complexes of human apolipoproteins A-I, A-II, C-I, C-II, C-III-1, and C-III-2 with egg phosphatidylcholine (egg-PC) and cholesterol were prepared by the cholate dialysis method. The complexes, isolated by gel filtration, had similar lipid and protein contents by weight, on the average: 1.77:0.083:1.0, egg-PC/cholesterol/apolipoprotein (w/w). The diameters of the discs, visualized by electron microscopy and estimated by gel filtration, ranged from 100 to 200 A. The alpha-helix content of the apolipoproteins in the complexes was from 50-72%, and their fluorescence properties indicated nonpolar, but quite varied environments for the tryptophan residues in the various complexes. Initial reactions of purified human lecithin: cholesterol acyltransferase with the complexes, adjusted to equal egg-PC concentrations, indicated that all the apolipoproteins activate the enzyme from 6-fold to 400-fold over control vesicles of egg-PC and cholesterol. In decreasing order of reactivity were the complexes with A-I, C-I, C-III-1, C-III-2, C-II, and A-II. These results indicate that aside from lipid-binding capacity and high amphipathic alpha-helix content, other structural features are required for optimal enzyme activation by apolipoproteins. Concentration and temperature dependence experiments gave similar apparent Km values, markedly different apparent Vmax, and very similar activation energies (about 19 kcal/mol), for the various complexes. These observations suggest that the rate-limiting enzymatic step of the reaction is common to all the complexes but that the activated enzyme levels differ from complex to complex. We propose that enzyme activation occurs upon binding to complexes via apolipoproteins. Addition of excess (5-fold) free apolipoprotein A-I or A-II to complexes resulted in the exchange of bound for free apolipoproteins and in loss of reactivity with the enzyme.

Apolipoprotein A-I↗
PubMed1984

A review of plasma apolipoprotein A-I interactions with phosphatidylcholines.

This review starts with a brief introduction to the properties of plasma high-density lipoproteins and their major protein component, apolipoprotein A-I, followed, in the following sections, by an account of experimental work from our laboratory on the interactions of apolipoprotein A-I with synthetic and natural phosphatidylcholines. The spontaneous reactions of phosphatidylcholine vesicles with apolipoprotein A-I are described in terms of the methods of observation, the properties of the reaction products (vesicular or micellar complexes of protein and lipid), and the kinetic controlling factors in the formation of the micellar products. A general detergent reconstitution method for the preparation of micellar complexes is presented, and applications of these particles in studies of the apolipoprotein-lipid interface and of enzymatic reactions are discussed.

Animals↗
PubMed1983

Reaction of lecithin:cholesterol acyltransferase with micellar complexes of apolipoprotein A-I and phosphatidylcholine, containing variable amounts of cholesterol.

In a continued investigation of lecithin:cholesterol acyltransferase reaction with micellar, discoidal complexes of phosphatidylcholine (PC) . cholesterol . apolipoprotein A-I (apo-A-I), we prepared well defined complexes with variable free cholesterol contents and examined their reactivity with purified enzyme. The complexes, prepared by the sodium cholate dialysis method, were fractionated into "small" and "large" classes by gel filtration of the reaction mixtures through a Bio-Gel A-5m column. The small complexes had egg-PC/cholesterol/apo-A-I molar ratios from 68:14:1 to 80:1:1, discoidal shapes with diameters around 114 (+/- 13) A and widths of 42 A by electron microscopy, and Stokes radii from 47 to 49 A corresponding to molecular weights near 2 X 10(5). The corresponding properties of the large complexes, isolated from samples with higher cholesterol contents, were egg-PC/cholesterol/apo-A-I molar ratios from 84:26:1 to 96:17:1, diameters of 161 (+/- 20) A, widths of 43 A, Stokes radii around 80 A, and estimated molecular weights in the vicinity of 5 X 10(5). Both types of complexes, when adjusted to equal apo-A-I concentrations, gave essentially identical initial reaction velocities with purified lecithin:cholesterol acyltransferase over a wide range of cholesterol concentrations (from 2 X 10(-7) to 4 X 10(-4) M), PC/cholesterol molar ratios (from 3:1 to 12:1), and quite different lipid fluidity conditions as detected by diphenylhexatriene fluorescence polarization. When complexes were adjusted to a constant cholesterol concentration, the initial velocities of the lecithin:cholesterol acyltransferase reaction followed Michaelis-Menten kinetics relative to the apo-A-I concentrations. Arrhenius plots of initial reaction rates for various complexes with variable cholesterol content and fluidity, measured at constant apo-A-I concentrations, gave identical temperature dependences with an average activation energy of 18.0 kcal/mol. These results strongly suggest that the cholesterol esterification on high density lipoprotein particles does not depend on their unesterified-cholesterol contents, PC/unesterified-cholesterol molar ratios, nor on the fluidity of their lipid domains.

Apolipoprotein A-I↗
PubMed1983

Time-dependent fluorescence intensity and depolarization of diphenylhexatriene in micellar complexes of apolipoprotein C-I and dimyristoylglycerophosphocholine.

The lipophilic fluorescent probe diphenylhexatriene was used to probe the lipid order and dynamics in apolipoprotein C-I . dimyristoylglycerophosphocholine (Myr2Gro-P-Cho) complexes. These complexes contain on the average 25 mol Myr2Gro-P-Cho/mol of apolipoprotein C-I, have a molecular weight around 200 000, and appear as discoidal, stacked particles by negative-stain electron microscopy. Steady-state fluorescence polarization of diphenylhexatriene as a function of temperature gives a broadened and shifted phase transition for Myr2Gro-P-Cho from the gel to liquid-crystalline state, with a mid-point around 27 degrees C. Time-dependent fluorescence intensity and anisotropy measurements of the diphenylhexatriene probe at 15 degrees C and 35 degrees C give fluorescence decay curves which can best be fit by two exponential functions, in each case. The fluorescence lifetimes and their fractional amplitudes approach the corresponding parameters in Myr2Gro-P-Cho vesicles and suggest insignificant effects of the protein on the microenvironment and conformations of the probe. The rotational correlation times and their fractional anisotropies indicate similar local motions of the probe in complexes and in vesicles, but reveal a significant ordering effect of the protein at both temperatures. The overall complex rotation at 15 degrees C has a correlation time of 136 +/- 13 ns, consistent with the size (approximately equal to 200 kDa) and shape (disc approximately equal to 5 x 15 nm) of the particle.

Apolipoprotein C-I↗
PubMed1983

Gluten-sensitive enteropathy: value of oral triglyceride loading test in the follow-up of patients on gluten challenge.

Oral triglyceride (TG) loading tests were performed in 31 patients with gluten-sensitive enteropathy (GSE) upon gluten challenge, and the results were compared with the mucosal histology. Of 19 prechallenge tests, 16 were in the normal range previously established in this laboratory (2-h postcibal plasma TG rise greater than or equal to 55 mg/dl) although values were lower (76 +/- 38 mg/dl, mean +/- SD) than those of healthy age-matched controls (116 +/- 34 mg/dl). Postchallenge tests performed in 29 patients (both symptomatic and asymptomatic) were all pathologic (postcibal TG rise 9 +/- 18 mg/dl). Three tests performed in two patients in whom GSE was ultimately not confirmed remained normal (postcibal TG rise 82 +/- 21 mg/dl) during a 24-mo follow-up. A significant correlation was demonstrated between the TG loading test and the mucosal pathology. The test is useful in the follow-up of patients of gluten challenge and in directing the postchallenge biopsy.

Administration, Oral↗
PubMed1982

Reaction of human lecithin: cholesterol acyltransferase with micellar substrates is independent of the phase state of the lipid.

Micellar complexes with different phosphatidylcholine (PC) compositions were prepared by the dialysis of PC-cholesterol dispersions with cholate in the presence of human apolipoprotein A-I (apo A-I). The complexes isolated by gel filtration had molecular weights around 200 000, two apo A-I molecules per particle, PC to apo A-I molar ratios from 91 to 123, and cholesterol to apo A-I molar ratios from 6 to 11. The phase-transition behavior of these complexes was examined by fluorescence polarization of diphenylhexatriene: the complexes containing dimyristoyl-PC had a transition temperature (Tm) of 32 degrees C, the complexes with dipalmitoyl-PC had a Tm of 45 degrees C, and those prepared with palmitoyloleoyl-PC were mostly present in the liquid-crystalline state in the temperature range investigated (55-7 degrees C). The initial velocities of the enzymatic reaction with purified human lecithin: cholesterol acyltransferase decreased in the order palmitoyloleoyl-PC greater than dipalmitoyl-PC greater than dimyristoyl-PC, at saturating micellar substrate levels. Arrhenius plots of the reaction rates from 15 to 41 degrees C were linear, and the activation energies ranged from 20 to 30 kcal/mol. These results indicate a marked dependence of the enzymatic reaction rates on the nature of the acyl donor, a dependence which is not related to the phase state of the bulk lipid in the micellar complexes.

Apolipoprotein A-I↗
PubMed1982

Nanosecond rotational motions of apolipoprotein C-I in solution and in complexes with dimyristoylphosphatidylcholine.

Human apolipoprotein C-I (apo C-I) in solution, in monomeric and oligomeric form, and in micellar complexes with dimyristoylphosphatidylcholine (DMPC), below and above the phase transition temperature of DMPC, was investigated with steady-state and time-resolved fluorescence methods. The environment of the Trp residue of apo C-I, in each physical state, was evaluated from fluorescence spectra and their changes upon KI quenching. Rotational correlation times of Trp residues were obtained from fluorescence anisotropy decay measurements. Static fluorescence anisotropy was determined as a function of temperature for the Trp residues of apo C-I in all physical states and for diphenylhexatriene dissolved in apo C-I X DMPC complexes. It was found that the Trp residues of apo C-I in solution are exposed from 75 to 88% to the aqueous medium, depending on the state of self-association. On the other hand, the Trp residues in apo C-I X DMPC complexes are only 42-45% exposed to KI quenching through an environment distinct from water. Apolipoprotein C-I in all its physical forms had two rotational correlation times associated with Trp motions: a longer one dependent on the size and flexibility of the entire particle and a very short one in the range from 0.2 to 0.4 ns. The later correlation times correspond to local Trp residue motions. These Trp motions were not significantly affected by a transition from the gel to the liquid-crystalline state of the lipid in apo C-I X DMPC complexes, suggesting that there is no coupling between the local motions of lipids and those of Trp side chains of apo C-I.

Apolipoprotein C-I↗
PubMed1982

Effect of dipalmitoylphosphatidylcholine vesicle curvature on the reaction with human apolipoprotein A-I.

Large unilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) were prepared by sonication and were fractionated by gel filtration on Sepharose Cl-2B in the size range from 180- to 380-A Stokes radii. Negatively stained electron micrographs of these preparations indicated the presence of unilamellar, spheroidal structures of the expected size. Fluorescence polarization of diphenylhexatriene, dissolved in the vesicles, revealed progressively broader phase transitions, shifted to lower temperatures for vesicles of decreasing sizes. The fractionated unilamellar vesicles and multilamellar vesicles of DPPC were reacted with human apolipoprotein A-I at 41 degrees C for periods from 1 to 120 h. The reaction mixtures were then passed through a Bio-Gel A-5m column to separate unreacted lipid vesicles and protein from micellar complexes of DPPC with apolipoprotein A-I. Smaller vesicles were much more reactive than larger vesicles or multilamellar vesicles with the apolipoprotein. This difference in reactivity was explained by the increasing bilayer curvature of smaller vesicles which changes the packing of DPPC molecules in the bilayer and facilitates its penetration by the apolipoprotein.

Apolipoprotein A-I↗