Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Isoelectric Point”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed1982

Isoelectric points of erabutoxins and monoacyl derivatives of erabutoxin b. Estimation of the pK values of amino groups in erabutoxins by using isoelectric-focusing data.

The isoelectric points of erabutoxins a, b and c, neurotoxic proteins of a sea snake, Laticauda semifasciata, were determined by density-gradient isoelectric focusing. The same measurement was also made with monoacyl derivatives of erabutoxin b, in which each one of all amino groups had been either acetylated or propionylated. Erabutoxins a and b showed the same isoelectric point at pH 9.68. The values for ]1-N alpha-acetyl-arginine]-, [15-N6-acetyl-lysine]-, [27-N6-acetyl-lysine]-, [47-N6-propionyl-lysine]- and [51-N6-acetyl-lysine]-erabutoxin b were at pH 9.52, 9.31, 9.45, 9.22 and 9.09 respectively, being definitely different from each other and lower than the value for the unmodified molecule. The isoelectric point of erabutoxin c, which is [51-asparagine]-erabutoxin b, was the same as that of [51-N6-acetyl-lysine]erabutoxin b. Assuming that no change in pK occurs on monoacylation, the pK values of amino groups in erabutoxin b were calculated from the isoelectric-point data. It is indicated that the pK values of zeta-amino groups differ markedly from each other and that the value of alpha-amino group is anomalously high.

Amino Acids↗
PubMed1990

An algorithm for the computer calculation of the coefficients of a polynomial that allows determination of isoelectric points of proteins and other macromolecules.

The isoelectric point (pI) of a macromolecule containing any number of acid-base residues can be expressed as a polynomial whose coefficients are related to both the number of acid-base residues present in the molecule and their K values. Polynomials of degree higher than 5 are too complicated to be solved manually. An algorithm is here presented which allows, with few sentences written in BASIC, the calculation of the polynomial coefficients. With this knowledge and using standard polynomial solving programs, the isoelectric point of the macromolecule can be calculated.

Algorithms↗
PubMed1997

Determination of the Surface Isoelectric Point of Oxide Films on Metals by Contact Angle Titration

The surface isoelectric point for the native air-formed oxide films on aluminum, chromium, and tantalum has been determined by measurement of contact angles at the hexadecane/aqueous solution interface as a function of pH of the aqueous phase. Application of Young's equation, the Gibbs equation, and surface equilibria conditions for hydroxylated oxide films leads to a mathematical expression which shows that the contact angle goes though a maximum at the isoelectric point of the oxide. The experimentally determined isoelectric point of oxide-covered chromium is 5.2 to 5.3, of oxide-covered aluminum is 9.5, and of oxide-covered tantalum is approximately -0.7. These values for the oxide films are within one to three pH units of the reported isoelectric points for the corresponding bulk oxide powders. The oxide-covered metal surfaces were cleaned by argon plasma treatment prior to measurement of contact angles, in that XPS measurements showed this treatment to be effective in reducing the thickness of the carbon contamination layer. In addition, interfacial tensions were measured at the hexadecane/aqueous solution interface and were observed to have only a slight dependence on the pH of the aqueous phase. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed1984

Isoelectric points of red clover necrotic mosaic virus serotypes.

Isoelectric focusing in agarose gel was used to determine the isoelectric points of red clover necrotic mosaic virus serotypes. The isoelectric points of serotypes A, B and C were in the pH ranges from 5.03-5.06, from 4.82-4.84 and from 4.60-4.62, respectively.

Isoelectric Point↗
PubMed1990

Shifts of isoelectric points between cellular and secreted antibodies as revealed by isoelectric focusing and immobilized pH gradients.

Charge microheterogeneity of monoclonal antibodies, as revealed by isoelectric focusing in carrier ampholytes, has been known for a long time. Here we demonstrate, in the case of monoclonals against the gp-41 of the HIV-1 virus, that this heterogeneity is already present within the cell sap of hybridoma cells during antibody synthesis. When the monoclonals are secreted extracellularly, the same isoelectric point (pI) spectrum is maintained, but there is marked redistribution of the relative isoform abundance towards the lower pI components. This suggests in vivo processing of such forms, possibly via glycosylation or deamidation. The secreted antibodies are also analyzed by immobilized pH gradients (IPG), where they demonstrate an even more extensive heterogeneity, due to the marked increment in resolving power. Single bands are purified by preparative IPGs in a multicompartment electrolyzer and are shown to be stable with time. Thus, artefactual heterogeneity produced by the focusing technique is completely excluded and cellular processing is clearly established.

Animals↗
PubMed1996

Molecular weights and isoelectric points of sperm antigens relevant to autoimmune infertility in men.

PURPOSE: We determined the molecular weights and isoelectric points of antigens in the uncapacitated and capacitated spermatozoa of fertile men binding to the serum immunoglobulin G (IgG) from 8 autoimmune infertile men and 8 fertile nonautoimmune men. MATERIALS AND METHODS: We used double fluorochrome cytotoxicity and immunobead binding assays to determine the sperm antibody status of the study subjects. 2-Dimensional gel electrophoresis and Western blot analysis were used to determine the molecular weights and isoelectric points of sperm antigens binding to serum IgG from these men. Amino acid sequencing of the digested peptides of chosen proteins was accomplished. Immune reactivity to the proteins in autoimmune infertile men was further verified. RESULTS: Serum IgG from fertile men failed to react significantly. Serum IgG from all autoimmune men (100%) showed significant binding to proteins with a molecular weight of 92 kDa. and isoelectric points of 3.5 to 4.0 in the capacitated spermatozoa. Six of 8 infertile men (75%) had serum IgG binding to capacitated sperm antigens with a molecular weight of 18 kDa. and isoelectric points of 4.5 to 5.2. Amino acid sequencing of peptides of the 92 kDa. protein matched complement component 1 (C1) inhibitor, with noted differences in the amino acid sequencing from the latter. The 18 kDa. protein matched calmodulin. We verified that serum IgG from autoimmune infertile men bound with C1 inhibitor and ascertained that the 92 kDa. protein in the spermatozoa was C1 inhibitor-like protein. CONCLUSIONS: Significant antibody responses to C1 inhibitor-like protein and calmodulin were noted in autoimmune men. Both of these proteins may be of testicular origin and these autoimmune responses may be highly relevant to infertility.

Amino Acid Sequence↗
PubMed1998

Delineating the specific influence of virus isoelectric point and size on virus adsorption and transport through sandy soils.

Many of the factors controlling viral transport and survival within the subsurface are still poorly understood. In order to identify the precise influence of viral isoelectric point on viral adsorption onto aquifer sediment material, we employed five different spherical bacteriophages (MS2, PRD1, Q beta, phi X174, and PM2) having differing isoelectric points (pI 3.9, 4.2, 5.3, 6.6, and 7.3 respectively) in laboratory viral transport studies. We employed conventional batch flowthrough columns, as well as a novel continuously recirculating column, in these studies. In a 0.78-m batch flowthrough column, the smaller phages (MS2, phi X174, and Q beta), which had similar diameters, exhibited maximum effluent concentration/initial concentration values that correlated exactly with their isoelectric points. In the continuously recirculating column, viral adsorption was negatively correlated with the isoelectric points of the viruses. A model of virus migration in the soil columns was created by using a one-dimensional transport model in which kinetic sorption was used. The data suggest that the isoelectric point of a virus is the predetermining factor controlling viral adsorption within aquifers. The data also suggest that when virus particles are more than 60 nm in diameter, viral dimensions become the overriding factor.

Adsorption↗
PubMed2004

Isoelectric point determination of norovirus virus-like particles by capillary isoelectric focusing with whole column imaging detection.

A capillary isoelectric focusing-whole column imaging detection (CIEF-WCID) method was used to determine the isoelectric point (pI) of norovirus virus-like particles (VLPs). The VLPs were produced from noroviruses that represented the two genogroups, genogroup I (Funabashi, Seto, and Norwalk) and genogroup II (Hawaii, Kashiwa, and Narita). Using the imaged CIEF-WCID detection technique, separation was accomplished using a short (4-5 cm) internally coated capillary (100-microm diameter) and a whole-column optical absorption imaging detector operated at 280 nm. CIEF-WCID experiments showed the similarity of the pI values of VLPs from genogroups I and II, with pI values of 5.9, 5.9, 6.0, and 6.0 for Funabashi, Norwalk, Seto, and Hawaii. The two other VLPs displayed pI values of 5.5 (Kashiwa) and 6.9 (Narita). The VLP peaks were shown to be reproducibility resolved. CIEF-WCID shows great promise for norovirus detection in public health, clinical, and food safety applications, as CIEF-WCID overcomes several limitations of the currently used genetic and immunological methods.

Electrophoresis, Capillary↗
PubMed1985

pH-dependent binding analysis, a new and rapid method for isoelectric point estimation.

Based upon the pH-dependent binding affinity of amphoteric molecules for an ion exchanger, and by taking advantage of batch procedures, a facile method was developed for estimating isoelectric points of these molecules. The new method allows pI measurements to be accomplished within 1 h. Moreover, any possible protein-ampholyte interaction or artifact formation, as may be introduced from the presence of carrier ampholytes when conventional focusing methods are employed, is eliminated by the method. In addition, because of the short processing time, isoelectric points of proteins can be measured at any desired temperature without much risk of protein denaturation. Seven proteins with well-defined isoelectric points were examined by the method. The measured pI values were within a range of 0.2 pH unit or less of the reported values. The precision of pI measurements by the method can be even further improved with the employment of a narrower pH gradient. Since the isoelectric point is an important parameter which governs much of the art of separating proteins, the advent of a simple and rapid method for its measurement would be of use for selecting the proper strategy for protein isolation and purification.

Binding Sites↗
PubMed1984

The importance of urinary immunoglobulin light chain isoelectric point (pI) in nephrotoxicity in multiple myeloma.

There is clinical and experimental evidence to imply that urinary immunoglobulin light chains are nephrotoxic yet some patients pass large amounts for years with little renal damage. Animal experiments suggest that a light chain is more nephrotoxic if it has a high isoelectric point (i.e. is cationic in relation to urine pH). We studied 23 patients with multiple myeloma, measuring light chain excretion rate, light chain isoelectric point (pI) and creatinine clearance. Light chain excretion rate was independent of light chain isoelectric point and did not correlate with creatinine clearance. Light chain isoelectric point correlated with creatinine clearance, suggesting that this characteristic may be an important determinant of the nephrotoxic effect of these immunoglobulin constituents.

Aged↗
PubMed1982

Isoelectric points and surface hydrophobicity of Gram-positive cocci as determined by cross-partition and hydrophobic affinity partition in aqueous two-phase systems.

Thirty-nine streptococcal strains belonging to groups A, C, and G and 12 staphylococcal strains were investigated with respect to surface charge and hydrophobicity. Isoelectric points of the bacteria were determined by cross-partition experiments in dextran-polyethylene glycol two-phase systems containing charged polymers. The results obtained indicate that group A, C, and G streptococci have isoelectric points of pH 3.75 +/- 0.15 standard deviation. Staphylococci show an isoelectric point of around pH 2 and thereby differ markedly from the streptococci. Pretreatment of bacteria with human serum resulted in a significant change in the isoelectric points of streptococci. In a second series of experiments, an aqueous dextran-polyethylene glycol two-phase system containing polyethylene glycol palmitate or stearate was used to study the hydrophobic surface properties of the bacterial cells. The partition of the staphylococci was not influenced by the addition of up to 1% (wt/wt) polyethylene glycol palmitate or stearate, whereas the streptococci showed a large variation in affinity for polyethylene glycol-bound hydrophobic groups. The bacterial strains included in the study were also tested for uptake of human serum proteins. A positive correlation was found between the hydrophobic affinity of group A streptococci and the density of receptors for aggregated beta-2-microglobulin.

Blood↗
PubMed1988

Isoelectric points of some sulfonamides: determination by microelectrophoresis and by calculations involving acid-base strength.

The isoelectric points of four very slightly soluble sulfonamides were measured by microelectrophoresis of dilute suspensions as a function of pH. Ionic strength and pH were adjusted with KCl, KOH, and HCl only. The isoelectric points were also calculated from published values of acid and basic ionization constants which had been determined by potentiometric titration, and from changes in ultraviolet absorption spectra and in solubility as a function of pH. Including one sulfonamide whose isoelectric point as measured by microelectrophoresis was published, rather good agreement between the two methods was observed for all but one compound. All values were between 3.5 and 4.6, indicating that the sulfonamides function as weak acids rather than as amphoteric compounds at physiological pH.

Chemical Phenomena↗
PubMedDate not supplied

Determination of the isoelectric points of low and high molecular mass ampholytes by capillary electrophoresis.

A methodology for a reliable and absolute determination of isoelectric points of amphoteric species by capillary zone electrophoresis is proposed. The principle of this absolute method consists in the application of an additional electroosmotic and/or hydrodynamic flow of a background electrolyte. This allows the measurement of electrophoretic mobilities of substances close to their isoelectric points where the net electric charge is very low and electrophoretic mobility tends to zero. The mobilities are measured at various pH values of the electrolyte so as to find the pH at which the substance moves through the separation column at zero mobility under the action of the additional flow only. The number of required measurements is lowered to the minimum with the help of the iterative procedure based on the Regula Falsi algorithm. The precision of the proposed method is predicted theoretically. The feasibility is demonstrated on real samples. The isoelectric points of histidine, myoglobine and ribonuclease are found from their titration curves.

Algorithms↗
PubMed1984

Plasma clearance, tissue distribution and catabolism of cationized albumins with increasing isoelectric points in the rat.

The infusion of cationic substances produces acute renal failure and proteinuria, and an experimental disease very similar to disseminated coagulopathy. The purpose of this work was to investigate further, in the rat, the plasma disappearance rate, the tissue distribution and the catabolism of albumins with modified isoelectric points. Human serum albumin was cationized with hexanediamine and labelled with 125I or 131I. During 10-180 min after their intravenous injection into the rat, these modified 125I-labelled albumins were cleared from the plasma at a rate which increased with their isoelectric point. At 1 and 3 h after the injection of highly cationic proteins (isoelectric point higher than 9.5) the tissue protein bound 125I concentration was greatest (approximately 3.5% of the injected activity/g) in the spleen and liver. A significant amount of the basic proteins was found in the kidney and in the lung (0.75-1%/g). Their concentration was much lower in other tissues. The whole body radioactivity was significantly lower 24 h after the injection of 131I-labelled cationized albumins than after similarly labelled native albumin. However, expressed as a percentage of the retention at 24 h, the body radioactivity at later times was higher for cationic than for native albumin. We conclude that cationized albumins are cleared from the plasma, mainly by the reticuloendothelial system, at a rate directly related to their isoelectric point. The cationized albumins are catabolized very rapidly initially, but a fraction of the injected protein remains in the body for a longer time than native albumin.

Animals↗
PubMed2003

Expression and purification of a recombinant avidin with a lowered isoelectric point in Pichia pastoris.

A recombinant glycosylated avidin (recGAvi) with an acidic isoelectric point was expressed and secreted by the methylotrophic yeast Pichia pastoris. The coding sequence for recGAvi was de novo synthesized based on the codon usage of P. pastoris. RecGAvi is secreted at approximately 330mg/L of culture supernatant. RecGAvi monomer displays a molecular weight of 16.5kDa, as assessed by ESI mass spectrometry. N-terminal amino acid sequencing indicates the presence of three additional amino acids (E-A-E), which contribute to further lowering the isoelectric point to 5.4. The data presented here demonstrate that the P. pastoris system is suitable for the production of recGAvi and that the recombinant avidin displays biotin-binding properties similar to those of the hen-egg white protein.

Amino Acid Sequence↗
PubMed1975

Relationship between in vivo degradative rates and isoelectric points of proteins.

Previous studies have shown that in mammalian cells proteins of large molecular weight are degraded more rapidly than small ones. Evidence is presented here that half-lives of proteins are also related to their isoelectric points. A double-isotope method was used to compare degradative rates of soluble proteins separated by isoelectric focusing. In rat liver, skeletal muscle, kidney, and brain, more rapid rates of catabolism were found for acidic protein fractions than for neutral or basic ones. Acidic proteins also tended to be degraded faster in several mouse tissues. A literature survey confirmed this trend. For 22 proteins from rat liver, a highly significant correlation was found between rates of degradation and isoelectric points (r = 0.824; P less than 0.01). This relationship between isoelectric point and half-life appears to be distinct from that between protein size and half-life.

Animals↗
PubMed2005

Solid-liquid interfacial energy as a tool to estimate shifts in isoelectric points of adsorbed proteins on solid surfaces.

This work reports the estimation of isoelectric points (pIs) of adsorbed amino acids and proteins on solid surfaces in the pH range between 3.5-11.0 from a measurement of solid/liquid interfacial energy. The values thus obtained are compared with the pIs determined in solution phase by other methods. Both glass and Teflon have been chosen as model solid surfaces. Close agreement between the reference pI values, obtained by the capillary isoelectric focusing and those obtained at solid/liquid interface is observed within an average difference of 0.04-0.08 pH unit when the pIs are above the pI of glass. For systems whose pIs are far away from that of glass (either in the acidic or highly alkaline range), a large shift in the isoelectric point is observed. In case of Teflon the pIs are closer to the reported values than at glass/liquid interface. This could be due to the fact that Teflon being a hydrophobic surface, its surface is dominated by dispersive forces, which may not be seriously affected by pH changes. The shift in the values at solid/liquid interface compared to that in solution have been examined using an 'image charge approach.'

Adsorption↗