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Detection of protease activities using specific aminoacyl or peptidyl p-nitroanilides after sodium dodecyl sulfate - polyacrylamide gel electrophoresis and its applications.

A general method for detecting protease activities on acrylamide or agarose gels after sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) using specific aminoacyl p-nitroanilide (NA) or peptidyl NA as substrate is described. This method is extended from the spectrophotometric assay of p-nitroaniline, which is a chromogenic product liberated by protease action on aminoacyl NA or peptidyl NA. The acrylamide gel containing protein bands was dipped directly into a solution which contained specific synthetic aminoacyl NA or peptidyl NA as a substrate or had been overlaid with an agarose gel containing the same substrate. The p-nitroaniline released on the acrylamide or agarose gel by the specific protease was diazotized with sodium nitrite and then coupled to N-(1-naphthyl)-ethylenediamine to produce distinct activity band(s). The substrates used for protease activity staining on gels were identical to those used for spectrophotometric assays. Some applications are described.

Benzoylarginine Nitroanilide↗

Engineering and biotechnological aspects for the manufacturing of high quality fried potato products.

Fried potato products have become very popular foods over the last decades. High quality standards have been established for these products by the food industry including uniform brown color and crispness. During frying, Maillard reactions takes place which contribute to color and taste development in these products. However, safety aspects are also influenced by these reactions, e.g., acrylamide formation. Maintaining high safety standards as well as the expected quality requires systematic research based on an integrated approach including all relevant variables, e.g., raw material properties, processing conditions and equipment concepts. Selected results of these investigations are presented and discussed, regarding influence of composition, e.g., precursor levels for Maillard reactions, treatment of raw materials and addition of reactants to frying fat. It has been demonstrated that a combined treatment of the potato sticks by coating of product surfaces and partial pre-drying can be successfully applied to produce well-browned French fries with lower acrylamide contents. Reductions up to 75% could be reached compared to samples without treatment. Furthermore, addition of a water/oil emulsion containing glutamine in the aqueous phase has been shown to influence Maillard reactions at the product surface, resulting in lower acrylamide contents at the same state of browning.

Biomedical Engineering↗

On the kinetics of monomer incorporation into polyacrylamide gels, as investigated by capillary zone electrophoresis.

The kinetics of monomer incorporation into a polyacrylamide gel have been studied in a photopolymerization system comprising 100 microM methylene blue in presence of a red-ox system, 1 mM sodium toluenesulfinate (reducer) and 50 microM diphenyliodonium chloride (oxidizer). A precise assessment of gel point (pc) was obtained in a droplet chamber, in which argon was gently bubbled with a fused silica capillary into the reaction mixture. At pc, 50% (+/- 3) acrylamide was incorporated into the matrix, vs. 80% (+/- 4) N,N'-methylenebisacrylamide. This incorporation level remained the same when polymerized in the 2-36 degrees C temperature range. Incorporation continued almost linearly for acrylamide up to 80% conversion. The reaction was continued up to 55 min (at 2 degrees C), at which point bisacrylamide had been essentially consumed (> 99.5% incorporation) and acrylamide had reacted (95%). At 2 degrees C, after gelation, the gel became progressively turbid (the Tyndall effect plateauing at 50 min), but it remained fully transparent if, at the gel point, reaction was continued at 50 degrees C. The consumption of the pendant double bonds of Bis followed the progression of turbidity. It is concluded that, by gelation at 2 degrees C, the nascent chains form clusters held together by hydrogen bonds (melting point at 28 degrees C); such clusters are subsequently "frozen" in the three-dimensional space as the pendant double bonds in the chains react progressively. Such turbid matrices are more porous and less elastic than when the gel is polymerized at 50 degrees C. This process is similar to the "lateral aggregation" occurring when gels are formed in presence of a polymer in solution (e.g. 10 KDa polyethylene glycol; Righetti et al., Electrophoresis 1992, 13, 587-594).

Acrylic Resins↗

Gradient polyacrylamide gel electrophoresis in presence of sodium dodecyl sulfate: a practical approach to muscle contractile and regulatory proteins.

Two gradient systems for polyacrylamide gel electrophoresis (PAGE) in the presence of sodium dodecyl sulfate (SDS) are described, with emphasis on improvements accumulated over two decades of studies on contractile proteins and regulatory enzymes from smooth muscle. The first "big slab" system utilizes 18 x 20 x 0.1 cm3 gels and a 10-18% acrylamide gradient, optimized for a high resolution of 10 to 500 kDa polypeptides. Eight (or more) gels are cast simultaneously with a gradient formation from "bottom to top" and 20% glycerol is added to the 18% acrylamide solution. The second "minislab" system represents an improved version of the system of Matsudaira and Burgess (Anal. Biochem. 1978, 87, 386-396), with 8 x 10 x 0.05 cm3 gels and 5-15% or 9-18% acrylamide gradient ranges. They are cast from "top to bottom" in 28-piece batches also with the addition of glycerol for improved gradient formation. Both types of gels can also be cast individually using a specially designed pestle-type gradient maker. For gel destaining, a convenient continuous hydrodynamic destainer is also described.

Actomyosin↗

Electrophoretic conditions for high resolution citrus isozymes in polyacrylamide gel electrophoresis.

Electrophoretic conditions including electrode and gel buffers, acrylamide concentration, use of stacking gels, voltage, current, and run time were investigated in order to produce isozyme bands of high resolution which would facilitate densitometric quantification of enzyme activity following polyacrylamide gel electrophoresis (PAGE). Electrode buffers which provided optimal conditions for gels stained for the isozymes of malate dehydrogenase (MDH), 6-phosphogluconate dehydrogenase (6-PGD), phosphoglucose isomerase (PGI), and shikimate dehydrogenase (SkDH) were 0.02 M Tris-glycine, pH 8.5, 0.1 M sodium borate, pH 6.0, 0.1 M sodium borate, pH 8.7, and 0.07 M sodium borate, pH 7.0, respectively. A 0.5 M Tris-HCl, pH 7.5, gel buffer was optimal for gels stained for the isozymes of 6-PGD, PGI and SkDH. A 0.5 M Tris-HCl, pH 8.5, gel buffer was best for gels stained for MDH. Stacking gels were found to be detrimental to enzyme activity and showed no improvement in resolution for any of the enzymes. Acrylamide concentration for gels stained for MDH were 8.7%, gels stained for 6-PGD and PGI were 7.5%, while gels stained for SkDH had an acrylamide concentration of 5.0%. Higher concentrations above these levels caused a reduction and in some cases loss of band activity, while below this concentration there was a decrease in band resolution.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol Oxidoreductases↗

DNA mobility anomalies are determined primarily by polyacrylamide gel concentration, not gel pore size.

The dependence of DNA mobility anomalies on gel pore size has been studied in polyacrylamide gels with a wide variety of compositions, using molecular weight ladders containing multiple copies of normal (12B) and anomalously slowly migrating (12A) 147-base pair restriction fragments from plasmid pBR322 as the migrating probe molecules. If the gel pore size is increased by decreasing the total acrylamide concentration (%T) at constant cross-linker ratio (%C), the usual method of increasing gel pore size, the mobility anomalies decrease with increasing gel pore radius as though the 12A multimers were retarded by a sieving mechanism. However, the decrease in the mobility anomalies is independent of whether the apparent gel pore radius is larger or smaller than the DNA radius of gyration, suggesting that gel pore size is not the controlling variable. If the acrylamide concentration is held constant and the gel pore size is increased by decreasing %C at constant %T, the mobility anomalies of the largest 12A multimers (6 mers and higher) decrease with increasing gel pore radius, because of sieving effects, until the effective gel pore radius becomes approximately equal to the DNA radius of gyration, after which the mobility anomalies level off and become independent of gel pore size. The mobility anomalies exhibited by 5-mers and smaller multimers of fragment 12A are independent of gel pore radius in all gels with constant %T. Similar results are observed with a molecular weight ladder containing phased A-tracts from the kinetoplast bending locus. Since the anomalous electrophoretic mobilities depend primarily on the total acrylamide concentration in the gel, and not on the apparent gel pore radius, increases in the magnitude of the mobility anomalies with increasing gel concentration (and decreasing gel pore radius) cannot be taken as evidence for DNA curvature.

Acrylic Resins↗

Prevention of artifactual protein oxidation generated during sodium dodecyl sulfate-gel electrophoresis.

Prevention of artifactual protein oxidation occurring during sodium dodecyl sulfate (SDS) acrylamide gel electrophoresis is critical for identifying physiological protein oxidation implicated in human diseases due to the routine use of gel electrophoresis to separate the multiple proteins in proteomic studies. To develop a methodology that completely prevents artifactual protein oxidation in SDS acrylamide gel electrophoresis, cytochrome c was electrophoresed on polyacrylamide gels and subjected to trypsin in-gel digestion followed by tryptic peptide analysis by mass spectrometry. It was found that degassing the acrylamide solution to remove molecular oxygen prior to gel polymerization is a crucial process to protect the electrophoresed protein from reactive oxygen species generated during electrophoresis. However, significant artifactual protein oxidation remains that can only be eliminated entirely, if proteins are electrophoresed on an SDS gel photopolymerized with flavin as the photoinitiator and thioglycolate included in the cathode buffer as a reactive oxygen species scavenger. Using this combination of methodologies, cytochrome c isolated from adult rat heart mitochondria was purified and digested followed by mass spectrometric analysis, demonstrating the requisite high resolution of the polyacrylamide gel and the entire elimination of artifactual oxidation.

Amino Acid Sequence↗

Macroporous polyacrylamide monolithic gels with immobilized metal affinity ligands: the effect of porous structure and ligand coupling chemistry on protein binding.

Macroporous polyacrylamide gels (MPAAG) with iminodiacetic acid (IDA) functionality were prepared by (i) chemical modification of polyacrylamide gel, (ii) co-polymerization of acrylamide with allyl glycidyl ether (AGE) and N,N'metylene-bis(acrylamide) (MBAAm) followed by coupling IDA ligand or (iii) by copolymerization of acrylamide and MBAAm with functional monomer carrying IDA-functionality (1-(N,N-bis(carboxymethyl)amino-3-allylglycerol). Screening for optimized conditions for the production of the MPAAG with required porous properties was performed in a 96-well chromatographic format that allowed parallel production and analysis of the MPAAG prepared from reaction mixtures with different compositions. Scanning electron microscopy of the fabricated MPAAG revealed two different types of the porous structures: monomodal macroporous structure with large interconnected pores separated by dense non-porous pore walls in case of plain gels or gels produced via copolymerization with AGE. The other type of the MPAAG (gel produced via co-polymerization with functional monomer carrying IDA-functionality) had bimodal pore structure with large interconnected pores separated by the pore walls pierced through with micropores. The effect of different modifications of MPAAG monoliths and of porous structure of the MPAAG (monomodal and bimodal porous structure) on protein binding has been evaluated.

Acrylic Resins↗

Dynamic features of the subunit interface of Cu,Zn superoxide dismutase as probed by tryptophan phosphorescence.

As part of the more general inquiry on the molecular basis of specific recognition between macromolecules, the subunit-subunit interface structure of dimeric superoxide dismutase from Photobacterium leiognathi has been probed selectively by the phosphorescence emission of Trp-73, located at the subunit contact region. Copper at the catalytic site was found to quench completely the delayed emission and therefore all studies were conducted with the copper-free or Cd(2+)-substituted protein. The spectrum at 140 K is diagnostic for an indole ring located in a hydrophobic environment whereas a degree of spectral broadening indicates that the local structure is not unique. Environmental heterogeneity is confirmed by the nonuniform phosphorescence decay in buffer, at 274 K, with lifetime components of 44 and 20 ms of practically equal amplitude. Information on the flexibility of the interface region was gathered from both the intrinsic lifetime and the accessibility of acrylamide to the site of the chromophore. The magnitude of the intrinsic lifetime, its temperature dependence, and the accessibility to solutes like acrylamide describe a tight dimeric structure in which hydrophobic interactions seem to play an important role. In particular the acrylamide bimolecular rate constant is 1.4 x 10(4) M(-1) s(-1) and indicates highly hindered diffusion of the solute through the interface region. Cd(2+) complexation to the apoprotein caused no detectable changes in protein conformation although the metal was able to influence the flexibility of the Trp-73 environment, indicating the occurrence of a long-range communication between the intersubunit surface and the active site, which is more than 16 A away.

Copper↗

Assessing the neurotoxic potential of methyl ethyl ketoxime in rats.

The potential of methyl ethyl ketoxime (MEKO) to produce neurotoxicity following acute and subchronic exposure was studied in rats. A Functional Observational Battery, assessment of motor activity, and neuropathology evaluations were conducted in the context of acute and subchronic toxicity studies. Three independent studies are reported: a pilot time-effect study designed to determine the time course and time to peak effect following a single high dose of MEKO, a single-dose neurotoxicity study, and a subchronic (13-week) repeated-dose neurotoxicity study in rats. An acrylamide-positive control group was included in the acute and subchronic studies for comparison with MEKO. Following an acute oral exposure of MEKO at a dose level of 900 mg/kg, locomotor activity was decreased compared to control with maximum decreases occurring between 30 and 60 min following oral administration. In the acute study, transient treatment-related changes in ease of cage removal, ease of handling, and in posture and gait were observed 1 hr after dosing with 900 mg/kg MEKO, as were significant depressions in motor activity. Following a single 300 mg/kg dose, transient MEKO-related changes in gait and aerial righting reflex were noted 1 hr after dosing. All effects were reversible within 24 hr of dosing. The single 100 mg/kg dose of MEKO was without observable effects. No acrylamide-related behavioral effects were noted following a single 50 mg/kg dose. In the subchronic study, transient treatment-related changes in ease of cage removal, ease of handling, and in posture, gait, and aerial righting were observed at the 400 mg/kg/day dose level when assessments were conducted immediately after dose administration. No consistent behavioral effects were observed prior to daily dose administration even after 13 weeks of exposure, indicating a lack of cumulative behavioral effect. No consistent behavioral changes were noted at doses of 125 mg/kg/day and below. Significant dose-related decreases in red cell mass, and increases in methemoglobin levels, reticulocyte, leukocyte, Heinz body counts, and spleen weights occurred at subchronic MEKO doses of 40 mg/kg/day and higher. No MEKO-related neuropathological changes occurred. Animals receiving acrylamide at 20 mg/kg/day showed expected behavioral and neuropathological changes consistent with peripheral neuropathy. In conclusion, high doses of MEKO can produce transient and reversible changes in neurobehavioral function consistent with central nervous system (CNS) depression. No evidence of cumulative neurotoxicity was detected. The hematopoietic system was effected at doses which did not produce detectable changes in CNS function.

Animals↗

Fluorescence studies of normal and sickle beta apohemoglobin self-association.

The acrylamide quenching of the intrinsic tryptophanyl fluorescence of normal and sickle beta apohemoglobins has been studied in 0.05 M potassium phosphate buffer, pH 7.5, at 5 degrees C over a protein concentration range from 1 to 50 microM. Analysis of quenching dynamics revealed a strong dependence on acrylamide concentration for the intrinsic fluorescence of both normal and sickle beta apohemoglobins, suggesting that one tryptophanyl residue [presumably that at position 37(C3)], was more accessible to collisional quencher than the other beta tryptophanyl residue [15(A12)]. Additional studies, which altered viscosity and subunit assembly experimental parameters, supported the assignment of residue 37 as the more dynamically accessible residue. Finally, the quenching data were also found to be dependent on protein concentration, implying that this difference in the mobility between the two residues is a sensitive probe of self-aggregation. Extrapolated dynamic quenching constants at low concentration of acrylamide were used to estimate the dimer-monomer equilibrium dissociation constants of normal and sickle beta apohemoglobins, and were found to be 5.6 and 2.4 microM, respectively, thus demonstrating distinct self-association properties of beta A and beta S apohemoglobins.

Apoproteins↗

A ligand-dependent conformational change of the Na+/galactose cotransporter of Vibrio parahaemolyticus, monitored by tryptophan fluorescence.

Purification and reconstitution of the active Vibrio parahaemolyticus Na+/galactose transporter (vSGLT) enables us to do protein chemistry studies on a representative member of this class of membrane transporters. By measuring intrinsic tryptophan (Trp) fluorescence, conformational changes on the binding of substrates could be investigated. Trp fluorescence increased by 6% on the addition of saturating levels of both Na+ and D-galactose, with a K0.5 for D-galactose of 0.6 mM. No change was seen on the addition of Na+ alone or by adding D-galactose in the presence of K+. The Trp fluorescence could be quenched by acrylamide, but not by Cs+or I?. In the presence of Na+ or K+ alone, of Na+ or K+ and D-galactose, of Na+ and L-glucose, or in the absence of ligands, the fluorescence quenches by acrylamide were similar. This indicated that the tryptophan exposure to acrylamide was unchanged in the presence or absence of ligands. No shifts in lem maximum were observed. To find the Trp responsible for the change in fluorescence, Trp 448 in transmembrane helix 11 in the putative sugar-binding pocket was mutated. It was found that W448F showed a similar change in Trp fluorescence upon the addition of D-galactose in the presence of Na+. We conclude that the Trp fluorescence properties of the purified and reconstituted Na+/galactose cotransporter are selectively changed by the transported substrates Na+ and D-galactose, but it is not the Trp (W448) in the sugar translocation pathway that is involved.

Calcium-Binding Proteins↗

Synchronous delivery systems composed of Au nanoparticles and stimuli-sensitive diblock terpolymer.

A method to construct synchronous delivery systems via direct self-assembly of Au nanoparticles on the poly[(N-isopropylacrylamide-r-acrylamide)-b-L-lactic acid] (PNAL) nanospheres has been presented in this paper. To achieve amphiphilic diblock terpolymer, hydrophobic poly (L-lactic acid) (PLLA) block was added to poly(N-isopropylacrylamide- r-acrylamide) (PNA) block via Michel-type addition reaction. Lower critical solubility temperature (LCST) was modulated at 35.6 degrees C which is close to the body temperature, but higher than poly(N-isopropylacrylamide) (PNIPAAm) homopolymer by controlling the ratio between isopropylacrylamide (IPAAm) monomers and acrylamide (AAm) monomers. Using this amphiphilic diblock terpolymer, PNAL nanospheres were fabricated by emulsion/evaporation technique followed by direct self-assembly of Au nanoparticles on the PNAL nanospheres due to the high affinity of amino groups donated from PNA block. The 'core' site of Au@PNAL nanospheres can load various lyphophilic drugs. Moreover, Au nanoparticles in the 'shell' domain of PNAL nanospheres give optimal environment to conjugate various biomolecules. Therefore, it is expected that Au@PNAL hybrid nanospheres can be utilized in synchronous delivery of both biomolecules in the 'shell' domain and various therapeutic drugs in the 'core' domain.

Acrylic Resins↗

Polyacrylamide gels which contain a novel mixed disulfide compound can be used to detect enzymes that catalyze thiol-producing reactions.

The synthesis of N-[5-(hydroxyethyl)dithio-2-nitrobenzoylaminoethyl] acrylamide (I) is described. If the disulfide bond in this compound is reduced with thiol reagents, an intense yellow color develops (epsilon 412 V 13,600 at pH 7.4) due to essentially the same chromophore as 5-thio-2-nitrobenzoic acid, the reduced form of 5,5'-dithiobis(2-nitrobenzoic acid)(Ellman's reagent). Polyacrylamide gels were prepared that were crosslinked with N,N'-methylenebisacrylamide and which contained I as an integral part of the polymerized acrylamide chain. Acetylcholinesterase (from electric eel and human brain tissue slices) and alkaline phosphatase (from Escherichia coli and calf intestine) were subjected to electrophoresis and then the gels were immersed in an appropriate thiol-substrate buffer (acetylthiocholine and cysteamine-S-phosphate, respectively). A yellow band developed rapidly in the acrylamide gel at the site of enzyme activity. Electrophoresis on the mixed disulfide-polyacrylamide gel proved to be a rapid and sensitive technique to detect very small amounts of enzyme (approximately 0.02 fmol acetylcholinesterase) and should have wide application for detecting other enzymes that hydrolyze thiol substrates.

Acetylcholinesterase↗

L-type pyruvate kinase from human liver. Purification by double affinity elution, electrofocusing and immunological studies.

L-type pyruvate kinase (ATP:pyruvate 2-O-phosphotransferase, EC 2.7.1.40) was highly purified from adult human liver. This purification included ammonium sulphate fractionation, DEAE-Sephadex batchwise absorption and two CM-Sephadex chromatographies with selective elution by ligands; in the former chromatography pyruvate kinase was eluted by ATP, in the latter one by phosphoenolpyruvate and fructose 1,6-diphosphate. The last step of the purification procedure involved a hydroxyapatite column chromatography. This purification procedure allowed us to obtain 3.6 mg of protein with a specific activity 190 I.U./mg, i.e. a 1200-fold purification with an overall yield of about 8%. This preparation was homogenous as judged by immunodiffusion, acrylamide and sodium dodecyl sulphate acrylamide gel electrophoresis. Anti L-type pyruvate kinase antibodies were obtained from rabbits and the antigenic properties of L-type pyruvate kinase were studied. The enzyme appeared to be a tetramer (molecular weight 220 000-240 000) with subunits of similar molecular weight about 60 000). Two interconvertible major forms were found by isoelectrofocusing in a sucrose gradient and in an acrylamide slab gel: one had an isoelectric point of 5.85 +/- 0.09 and was the major enzymatic form after incubation with fructose 1,6-diphosphate or high concentrations or SH reagents. The other form (isoelectric point 6.28 +/- 0.03) was the major form of L-type pyruvate kinase in liver crude extract, and after incubation of purified enzyme with a proteic fraction isolated from liver extract by ammonium sulphate precipitation.

Chromatography, Affinity↗

The process in which nucleotide is buried into the active site of heavy meromyosin.

The process in which nucleotide is buried into the active site of heavy meromyosin was studied with stopped-flow apparatus by monitoring the time-course of the large fluorescence increase of 1,N6-ethenoadenosine triphosphate (epsilon-ATP) when it binds from acrylamide-containing solutions. We have recently reported that free epsilon-ATP fluorescence is effectively quenched by acrylamide while bound epsilon-ATP is resistant to quenching by acrylamide. In the present study it was found that in the first step the phosphate moiety binds at a high rate, while the adenine moiety is still on the rim of the active site; the adenine moiety is then pulled into a crevice, and finally epsilon-ATP hydrolysis occurs.

Adenosine Triphosphatases↗

Human placental oxytocinase and its relationship to pregnancy plasma oxytocinase.

Plasma "oxytocinase of pregnancy" and three placental "oxytocinase" fractions from human placental extracts were compared. On the basis of acrylamide-agarose chromatography, polyacrylamide gel electrophoresis, substrate specificity, heat liability and relative insensitiveness to L-methionine, it is concluded that placental enzyme activities, present in the second acrylamide-agarose peak, are identical with the plasma "pregnancy oxytocinase" and are to be regarded as its source. The hypothesis of a transplacental passage of placental peak II oxytocinase in the blood compartment of the mother seems well supported. Heat treatment of the placental extracts uncovered a minor activity behaving like Oya's microsomal oxytocinase, which is totally unlike the plasma oxytocinase and plays no part in the increased oxytocinase activity of human pregnancy plasma. A hitherto undescribed enzyme activity shares with the pregnancy oxytocinase its specificity towards L-leucyl-beta-naphthylamide and di-S-S-L-cysteinyl-beta-naphthylamide, its heat lability and realtive insensitiveness to L-methionine. However, this activity is carried by a protein of much lower molecular weight as judged by acrylamide-agarose chromatography, which shows only a single activity band on polyacrylamide gel electrophoresis.

Acid Phosphatase↗

Imidazole-SDS-Zn reverse staining of proteins in gels containing or not SDS and microsequence of individual unmodified electroblotted proteins.

A reverse staining procedure is described for the detection of proteins in acrylamide and agarose gels with and without SDS. Protein detection occurs a few minutes after electrophoresis. The sensitivity on acrylamide gels is higher than that of Coomassie blue staining either on acrylamide gels or on electrotransferred membranes. Sequencing of protein bands only detected by reverse staining on the gel and not by Coomassie blue is demonstrated.

Electrophoresis, Agar Gel↗