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Biomedical subjects

I Simon

Publications and source records attributed to I Simon.

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

Investigation of protein refolding: a special feature of native structure responsible for refolding ability.

A possible origin of the refolding ability of globular proteins is discussed. It is shown that the structure of native proteins has a special feature, namely, that this is the only structure in which the short overlapping segments of the polypeptide chain are in one of the significantly stable conformations of the oligopeptides with the same amino acid sequences as segments themselves. It is shown that this special feature is responsible for the refolding ability of proteins. A simple formula is given for the estimation of the time, t, necessary for the spontaneous formation of a refolding nucleus by a certain segment and it is shown that the segment which has the smallest t value, will serve as a refolding nucleus. It is suggested that natural selection which ensures the maintenance of the native structure of globular proteins automatically results in the refolding ability of proteins regardless of the biological relevance of this ability.

Amino Acid Sequence↗
PubMed1985

Conformation of human IgG subclasses in solution. Small-angle X-ray scattering and hydrodynamic studies.

The structure of six human myeloma proteins: IgG1(Bal), IgG2(Klu), IgG3(Bak), IgG3(Het), IgG4(Kov) and IgG4(Pol), was studied in solution using small-angle X-ray scattering and hydrodynamic methods. For IgG1(Bal) and IgG3(Het) the experimental data, including radius of gyration (Rg degree), radii of gyration of the cross-section (Rq1, Rq2), intrinsic viscosity [eta], sedimentation coefficient (S degree 20,w) and molecular mass, were interpreted in terms of structural models based on the Fab and Fc conformations, observed in crystal, by varying the relative positions of the Fab and Fc parts, i.e. their relative angles and distances. The values Rg degree = (6.00 +/- 0.05) nm, S degree 20,w = (6.81 +/- 0.10) S and [eta] = 0.0062 +/- 0.0005 cm3/mg obtained for IgG1(Bal) are compatible with a planar model in which the angle between the Fab arms is about 120 degrees. For IgG3(Het) the following data were obtained: Rg degree = (4.90 +/- 0.05) nm, S degree 20,w = (6.32 +/- 0.01) S and [eta] = (0.0065 +/- 0.0005) cm3/mg. The apparent contradiction between the higher molecular mass and lower Rg degree and S degree 20,w values for IgG3(Het) in comparison to IgG1(Bal) can be resolved by proposing a 'non-planar' (tetrahedral) molecular shape, in which the long hinge peptide is in a folded conformation and the two Fab and Fc parts are in a closely packed arrangement. In this model the angle between the two Fab arms is about 90 degrees, in the average position. The X-ray scattering and hydrodynamic behaviour of the IgG2 and IgG4 types of antibodies appeared to be similar to IgG1(Bal). The parameters of the two IgG3 proteins are similar while they are different to the others.

Amino Acids↗
PubMed1985

The effect of iron binding on the conformation of transferrin. A small angle x-ray scattering study.

Distance distribution functions, p(r), radii of gyration, Rg, and radii of gyration of cross section, Rq, of apotransferrin, monoferric transferrin, and diferric transferrin have been compared. The alteration of Rg and Rq upon iron binding has been determined by a difference method. An unusual feature of the stepwise structural changes of transferrin upon iron saturation is that binding of the first ferric ion is responsible for more than half of the whole change in Rq, whereas Rg alters significantly only after the binding of the second ferric ion.

Humans↗
PubMed1984

Electron-spin resonance studies of lipid-modified microsomes from Friend erythroleukemia cells.

The fatty acid composition of cultured Friend erythroleukemia cells was modified by supplementation of the medium with oleic or linoleic acid. There was a 30% reduction in saturated and a 35% reduction in polyunsaturated fatty acids in microsomal phospholipids when the cells were grown in media supplemented with oleic acid, and a 3-fold increase in polyunsaturated fatty acids when the cells were grown in linoleic acid-supplemented media. Electron-spin resonance studies with the 5- nitroxystearate probe demonstrated that there was no appreciable change in microsomal lipid mobility as measured by the order parameters. In contrast, changes in lipid mobility were detected with the spin-label probe when microsomes were first isolated from Friend erythroleukemia cells and subsequently modified by incubation with liposomes composed of either dioleoyl- or dilinoleoylphosphatidylcholine plus bovine liver phospholipid-exchange protein. The fatty acid compositional changes produced in these microsomes were similar to those obtained when the intact cells were grown in media containing supplemental fatty acids. These findings indicate that the lipid mobility of Friend cell microsomes can be altered by phospholipid replacements in vitro, but that this does not occur when similar microsomal fatty acid modifications are produced during culture of the intact cell.

Animals↗
PubMed1984

Abnormal insulin binding and membrane physical properties of a Friend erythroleukemia clone resistant to dimethylsulfoxide-induced differentiation.

We have compared insulin binding, plasma membrane fluidity, and phospholipid composition of three different Friend erythroleukemia clones, a wild type (FLC) a mutant (R3) and the revertant to wild type F+. The R3 clone is a non-differentiating DMSO-resistant clone (R3) and has altered membrane fluidity and dramatically altered insulin-binding properties. The receptor of R3 bound insulin as if it possessed a single class of low affinity receptors that lacks the property of negative cooperativity. The Scatchard plot is linear and there is no ligand-induced acceleration of dissociation. The Hill coefficient for R3 is 1, implying 'no cooperativity', whereas the Hill coefficient for the two DMSO-inducible clones, (FLC and F+) is 0.3, implying 'negative cooperativity'. In addition, the insulin receptor of R3 has a decreased affinity for insulin, manifested as a 40-fold increase in the amount of insulin required to compete for half of the tracer binding (41 nM for R3 vs. 1 nM for FLC and F+). Computer-fitted Scatchard plots analyzed by the negative cooperativity model reveal that R3 has 95 000 receptor sites/cell, with a high affinity constant Ke of 0.016 nM-1, and a low affinity constant, Kf of 0.012 nM-1. Both DMSO-inducible clones have about 40 000 receptor sites/cell with Ke of 0.11 nM-1 and Kf of 0.02 nM-1. Electron spin resonance measurements with the 5-nitroxy stearate spin probe demonstrate that R3 had a more fluid plasma membrane than the FLC and F+ clones. The lipid composition of R3 is different from that of the DMSO-inducible clones. The weight ratio for unsaturated fatty acids to saturated fatty acids for R3 is 2.5, and the FLC clone has a lower ratio of 1.9. These results are consistent with our earlier findings in FLC that very high membrane fluidity is associated with alterations in the binding properties of the insulin receptor.

Animals↗
PubMed1984

The diffusion of water across the stratum corneum as a function of its water content.

The flux of tritiated water (HTO) through pieces of stratum corneum at four different levels of hydration has been measured. The concentration of water in the stratum corneum, the concentration of HTO in the presenting solution, and the thickness, density, and weight per unit area of the dry stratum corneum are known. The thickness of the hydrated stratum corneum and the permeability and diffusion constants of HTO were calculated. From these in vitro data it is possible to calculate the in vivo thickness of the stratum corneum, its water concentration profile, and the flux of water (transepidermal water loss) at environments of different relative humidities. Both the transepidermal water loss and the water concentration profile change very little as the environmental relative humidity increases from 0 to 80%. The small decrease in the water concentration of the surface layers of cells as the relative humidity becomes very low, however, may cause an observable alteration in the physical characteristics of the surface layers.

Body Water↗
PubMed1984

[Not Available].

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Bible↗
PubMed1984

[Not Available].

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Bible↗
PubMed1983

Phospholipid fatty acid modification of rat liver microsomes affects acylcoenzyme A:cholesterol acyltransferase activity.

The effect of phospholipid fatty acyl composition on the activity of acylcoenzyme A:cholesterol acyltransferase was investigated in rat liver microsomes. Specific phosphatidylcholine replacements were produced by incubating the microsomes with liposomes and bovine liver phospholipid-exchange protein. Although the fatty acid composition of the microsomes was modified appreciably, there was no change in the microsomal phospholipid or cholesterol content. As compared to microsomes enriched for 2 h with dioleoylphosphatidylcholine, those enriched with dipalmitoylphosphatidylcholine exhibited 30-45% less acyl-CoA:cholesterol acyltransferase activity. Enrichment with 1-palmitoyl-2-linoleoylphosphatidylcholine increased acyl-CoA:cholesterol acyltransferase activity by 20%. By contrast, dilinoleoylphosphatidylcholine abolished microsomal acyl-CoA:cholesterol acyltransferase activity almost completely. Addition of cofactors that stimulated microsomal lipid peroxidation inhibited acyl-CoA:cholesterol acyltransferase activity by only 10%, however, and did not increase the inhibition produced by submaximal amounts of dilinoleoylphosphatidylcholine. Certain of the phosphatidylcholine replacements produced changes in palmitoyl-CoA hydrolase, NADPH-dependent lipid peroxidase, glucose-6-phosphatase and UDPglucuronyl transferase activities, but they did not closely correlate with the alterations in acyl-CoA:cholesterol acyltransferase activity. Electron spin resonance measurements with the 5-nitroxystearate probe indicated that microsomal lipid ordering was reduced to a roughly similar extent by dioleoyl- or by dilinoleoylphosphatidylcholine enrichment. Since these enrichments produce widely different effects on acyl-CoA:cholesterol acyltransferase activity, changes in bulk membrane lipid fluidity cannot be the only factor responsible for phospholipid fatty acid compositional effect on acyl-CoA:cholesterol acyltransferase. The present results are more consistent with a modulation resulting from either changes in the lipid microenvironment of acyl-CoA:cholesterol acyltransferase or a direct interaction between specific phosphatidylcholine fatty acyl groups and acyl-CoA:cholesterol acyltransferase.

Acyl Coenzyme A↗
PubMed1983

[Methods and their evaluation for the estimation of vitamin B6 levels in man. 5. Serum pyridoxal-5-phosphate determination: method and comparison of methods].

Methods and Their Evaluation to Estimate the Vitamin B6-Status in Human Subjects. V. S-PLP-Determination: Method and Comparison of Methods. A method to determine the plasma pyridoxal 5-phosphate (PLP) basing on the enzymatic decarboxylation of 1-14C-l-tyrosine and the measurement of the radio-active 14CO2 is described. Its efficiency is discussed in comparison with other methods. High specificity, precision, accuracy, and sensitivity are demonstrated. The developed equipment allows to analyse a great number of samples and minimizes the risk of radio-active contamination. The commercial apoenzyme preparations are different in quality and require purification. Apoenzyme lots with high genuine content of PLP are useless. Storage tests at 4 degrees C, -18 degrees C, and -196 degrees C show stability of the samples for one day, 30 days, and at least 10 weeks.

Carbon Radioisotopes↗
PubMed1982

Hydrogen exchange and the dynamic structure of proteins.

In native proteins, buried, labile protons undergo isotope exchange with solvent hydrogens, but the kinetics of exchange are markedly slower than in unfolded polypeptides. This indicates that, whereas buried protein atoms are shielded from solvent, the protein fluctuates around the time average structure and occasionally exposes buried sites to solvent. Generally, hydrogen exchange studies are designed to characterize the nature of the fluctuations between conformational substates, to monitor the shift in conformational equilibria among protein substates due to ligand binding or other factors, or to monitor the major cooperative denaturation transition. In this article, we review the recent reports of hydrogen exchange in proteins, focusing on recent advances in methodology, especially with regard to the implications of the results for the mechanism of hydrogen exchange in folded proteins.

Crystallization↗
PubMed1982

De novo methylation and expression of retroviral genomes during mouse embryogenesis.

Retrovirus genomes introduced into mouse zygotes by microinjection of cloned DNA, or into morula stage pre-implantation mouse embryos by infection with Moloney murine leukaemia virus (M-MuLV), became de novo methylated and were blocked in expression. No restriction of virus expression and no de novo methylation were observed when post-implantation mouse embryos were infected with virus. Efficient de novo methylation activity may be an important characteristic of gene regulation in early mouse embryos.

Animals↗
PubMed1982

Electron spin resonance studies on intact cells and isolated lipid droplets from fatty acid-modified L1210 murine leukemia.

It has been suggested that the formation of cytoplasmic lipid droplets may produce an artifact and be responsible for the differences in membrane physical properties detected in lipid-modified cells using fluorescence polarization or spin label probes. To investigate this, the electron spin resonance spectra of lipid droplets isolated from the cytoplasm of L1210 leukemia cells were compared with spectra obtained from the intact cell. Mice bearing the L1210 leukemia were fed diets containing either 16% sunflower oil or 16% coconut oil in order to modify the fatty acid composition of the tumor. A microsome-rich fraction prepared from L1210 cells grown in animals fed the sunflower oil-rich diet contained more polyenoic fatty acids (52 versus 29%), while microsomes from L1210 cells grown in animals fed the coconut oil-rich diets contained more monoenoic fatty acids (37 versus 12%). The order parameter calculated for lipid droplets labeled with the 5-nitroxystearic acid spin probe was only about one-half that of intact cells, whereas it was similar to that obtained for pure triolein droplets suspended in buffer. Order parameters of the inner hyperfine splittings calculated from the spectra of cells grown in the sunflower oil-fed animals [0.543 +/- 0.001 (S.E.)] were lower than those from the cells grown in animals fed the coconut oil diets (0.555 +/- 0.002) (p less than 0.005). In contrast, the order parameters of the lipid droplets isolated from the cells grown in animals fed sunflower oil (0.303 +/- 0.029) or coconut oil (0.295 +/- 0.021) were not significantly different, indicating that motion of a spin label probe in the highly fluid cytoplasmic lipid droplets is not affected by these types of modifications in cellular fatty acid composition. Therefore, the electron spin resonance changes that are observed in the intact cells cannot be due to localization of the probe in cytoplasmic lipid droplets. These results support the conclusion that the electron spin resonance changes observed with the 5-nitroxystearic acid spin probe are due to changes in membrane fluidity produced by the modification in cellular lipid composition.

Animals↗
PubMed1982

[Methods and their evaluation in the determination of vitamin B6 status in man. 2. alpha-SGOT: reliability of the parameter].

Some factors, which are primary independent of the vitamin B6-uptake have influence on the maximum and/or the basis activity of the EGOT and thereby finally on the alpha-value. There is a negative correlation between the age of the test persons and both the maximum and the basis activity. An insufficient supply with protein leads to lowered maximum activities, but we could not estimate a correlation between EGOT+ and protein-intake when adequate. Influences of oral contraceptives as well an enzyme induction caused by long-term high vitamin B6-uptake can not confidently be excluded. Specific differences between the enzyme activities of men and women are scarcely probable. EGOT+ and EGOT- are lowered by chronic alcohol abuse. A short-term load with alcohol does not change the results. Oral contraceptives as well as the vitamin B2 status have little if any influence on the enzyme activities. Our results show, that because of the various possible influences a single determination of the alpha-value is a doubtfull parameter to assess the vitamin B6 status of men. Only the observation of the alteration of the individual alpha-value during deficiency and substitution tests, considering at the same time some essential incidentals, can lead to well-founded statements.

Adult↗
PubMed1982

[Methods and their evaluation in estimating the vitamin B6-status in humans. 3. Determination- of 4-pyridoxic acid in urine].

A method based on the fluorimetric determination of the 4-PA-lactone is described. The applied method saves time and work compared to others. The analytical procedure may be interrupted for a few days after eluting the 4-PA from the ion exchanger as well as before measuring the transmission. Accuracy, precision and sensitivity of the method are demonstrated. Interfering substances influencing the fluorescence measurement and probable errors caused by the reference value creatinine are discussed. Storage tests applied with the urine samples at--18 degrees C have shown that 4-PA-values do not change considerably within two months.

Chromatography, Ion Exchange↗
PubMed1982

[Methods and their evaluation in estimating the vitamin B6-status in humans. 4. 4-PA: reliability of the parameters].

Effects of physiological factors on 4-PA-excretion of more than 400 industrial workers and students were examined. Borderline values are discussed. With increasing age men as well as women showed significant higher 4-PA-values. After optimizing the vitamin B6-uptake by means of vitamin administration the differences disappear. Age-depending variations in the ability forming 4-PA are not likely. The higher 4-PA-excretion of men is probably due to better dietary supply rather than to sex differences in metabolising the vitamin. There are no considerable influences on the parameter by oral contraceptives Short-term variations of dietary vitamin B6-supply have striking effects on the 4-PA-excretion and restrict the reliability of this parameter. An insufficient vitamin B2-supply can stimulate a marginal vitamin B6-status. Alcohol consumption the day before does not change the 4-PA-excretion.

Adult↗