Inhibitory properties of endogenous subunit epsilon in the Escherichia coli F1 ATPase.

Homogeneous ? bound tightly to the purified Escherichia coli ATPase (ECF₁ from which ? had been removed and strongly inhibited its ATPase activity. ECF₁ containing ? had a lower specific activity than ECF₁ missing ?, provided that the ATPase assay was carried out at relatively high concentrations of enzyme. Antiserum specific for the ? subunit stimulated the ATPase, as did diluting the enzyme, apparently by dissociating ?. When the ATPase reaction was started by the addition of enzyme, the rate of ATP hydrolysis increased progressively during the first 3 min until a linear steady-state rate was reached. A prior incubation with ATP abolished the lag period and ADP prevented the ATP effect. ECF₁ missing ? gave a linear rate of ATP hydrolysis without a lag, unless ? was rebound to it before the assay. These results suggest that ECF₁ as purified is in an inhibited state due to the presence of the ? subunit, whose interaction with ECF₁ is governed by an equilibrium binding. ATP appears to convert ECF₁ to a form which more readily binds and releases ?.     

A fluorescence assay for 4'-(9-acridinylamino)methanesulfon-m-anisidide, a new antitumor agent.

A sensitive fluorescent method is described for the detection of 4′-(9-acridinylamino)-methanesulfon-m-anisidide (AMSA) in serum. The assay is based on the alkaline hydrolysis of AMSA into 9(10H)-acridone. While AMSA has negligible fluorescence, 9(10H)-acridone fluoresces brilliantly (excitation 266 nm, emission 470 nm). The assay is shown to be linear from 0.01 to 1.0 μm. In addition, the assay is shown to be useful, in conjunction with an ethyl acetate extraction, in distinguishing serum levels of parent AMSA from metabolized or protein-bound AMSA.     

Collagenase induced changes in the circular dichroism spectrum of collagen

The maximum at 220 nm in the circular dichroism spectrum of native collagen solution changed to a negative value after heat denaturation or collagenase hydrolysis. The enzyme induced rate of CD change at 220 nm was shown to be first order in collagen concentration. The specific rate constant k is actually a combined rate constant k_fast and k_slow in which the ratio k_f/k_s is 4.1. The initial rates were linear with respect to enzyme concentration, and the K_m was found to be 5.5 × 10^?7 M. The rate of ultraviolet hyperchromicity at 220 nm on collagen hydrolysis was determined. The k_fast was the same as that obtained by CD. The k_f/k_s ratio was 4.6. Both methods may be readily used to assay for collagenase activity.     

Bull semen nicotinamide adenine dinucleotide nucleosidase. VI. Fluorescence studies of the enzyme with reduced nicotinamide adenine dinucleotide

The binding of NADH to bull semen NAD nucleosidase was observed to be accompanied by a considerable enhancement of the fluorescence of NADH. The fluorescence enhancement observed in the binding of NADH to the enzyme was utilized to study the stoichiometry of binding of this compound to the enzyme. Results obtained from the fluorescence titration of the enzyme with NADH indicated the binding of one mole of NADH per mole of enzyme (36,000 g). The dissociation constant for the enzyme-NADH complex was determined to be 2.52 × 10^?6m. NADH was also found to be a very effective competitive inhibitor of the NADase-catalyzed hydrolysis of NAD, and the inhibitor dissociation constant (K_I) for the enzyme-NADH complex was determined to be 2.99 × 10^?6m which was in good agreement with the value obtained from the fluorescence titration experiments.     

Specific spectrophotometric assays for cathepsin B1.

Cathepsin B₁ from bovine spleen was partially purified by acetone fractionation and by chromatography on Sephadex G-150 and DEAE Sephadex A-50. The enzyme was shown to catalyze the hydrolysis of p-nitrophenyl benzyloxycarbonylglycinate and p-nitrophenyl α-N-benzyloxycarbonyl-l-lysinate. Under the assay conditions, cathepsin B₁ is the major enzyme present in bovine spleen homogenates hydrolyzing these substrates. The kinetic parameters for the hydrolysis of p-nitrophenyl benzyloxycarbonylglycinate and p-nitrophenyl α-N-benzyloxycarbonyl-l-lysinate were measured and compared with those obtained for other cathepsin B₁ substrates. These results form the basis of an improved spectrophotometric assay for this enzyme in which the liberation of p-nitrophenol from either the N-benzyloxycarbonyl glycine or lysine p-nitrophenyl ester is monitored continuously at 326 nm.     

Mutations of Trp275 and Trp397 altered the binding selectivity of Vibrio carchariae chitinase A

Point mutations of the active-site residues Trp168, Tyr171, Trp275, Trp397, Trp570 and Asp392 were introduced to Vibrio carchariae chitinase A. The modeled 3D structure of the enzyme illustrated that these residues fully occupied the substrate binding cleft and it was found that their mutation greatly reduced the hydrolyzing activity against pNP-[GlcNAc]₂ and colloidal chitin. Mutant W397F was the only exception, as it instead enhanced the hydrolysis of the pNP substrate to 142% and gave no activity loss towards colloidal chitin. The kinetic study with the pNP substrate demonstrated that the mutations caused impaired K_m and k_cat values of the enzyme. A chitin binding assay showed that mutations of the aromatic residues did not change the binding equilibrium. Product analysis by thin layer chromatography showed higher efficiency of W275G and W397F in G4–G6 hydrolysis over the wild type enzyme. Though the time course of colloidal chitin hydrolysis displayed no difference in the cleavage behavior of the chitinase variants, the time course of G6 hydrolysis exhibited distinct hydrolytic patterns between wild-type and mutants W275G and W397F. Wild type initially hydrolyzed G6 to G4 and G2, and finally G2 was formed as the major end product. W275G primarily created G2–G5 intermediates, and later G2 and G3 were formed as stable products. In contrast, W397F initially produced G1–G5, and then the high-M_r intermediates (G3–G5) were broken down to G1 and G2 end products. This modification of the cleavage patterns of chitooligomers suggested that residues Trp275 and Trp397 are involved in defining the binding selectivity of the enzyme to soluble substrates.     

The hydrolysis of 3-(2-furylacryloyl)-glycyl-l-leucine amide by thermolysin

The kinetics of the hydrolysis of 3-(2-furylacryloyl)-glycycl-l-leucine amide by thermolysin has been reinvestigated. It was found that the K_m for the enzyme substrate interaction is 2.5 × 10^?3m at pH 7.2. This K_m is an order of magnitude less than what has been previously assumed to be the K_m for the enzyme-substrate interaction. The normally recommended assay has 1–3 × 10^?3m substrate and is based on the assumption that the substrate concentration is much less than the K_m. Our data indicate that this assumption appears to be invalid. The hydrolysis of 3-(2-furylacryloyl)-glycyl-l-leucine amide results in a maximum decrease in absorbance at 322 nm. The change in absorbance is nearly 10-fold greater at 322 nm than the change in absorbance at 345 nm where the hydrolysis has been customarily followed. By following the hydrolysis of the substrate at 10^?4m at 322 nm it is possible to work under conditions where the substrate concentration is much less than the K_m.     

Observation of two quenchers of chlorophyll fluorescence in chloroplasts at −196°C

Fluorescence induction at ?196°C has been monitored in chloroplasts rapidly frozen after poising at different redox potentials at room temperature. It was found that, as at room temperature, the initial level of fluorescence observed upon shutter opening (F_o), relative to the final level observed after 10 seconds of illumination (F_m) increased as the redox potential of the chloroplasts was lowered. Redox titration revealed the presence of two quenching components with E_m,7.8 at ?70 mV and ?275 mV accounting for approx. 75% and 25% of the variable fluorescence (F_v). Parallel observation of fluorescence yield at room temperature similarly gave two components, with E_m,7.8 at ?95 mV and ?290 mV, also accounting for approx. 75% and 25%. Simultaneous measurement of fluorescence emission at ?196°C at 695 nm and 735 nm indicated that both emissions are quenched by the same redox components.     

Assay of the enzymatic hydrolysis of pantetheine

Four rapid, independent assays of enzymatic pantetheine hydrolysis are described and compared using an enzyme partially purified from pig kidney. Two assays detect specifically the hydrolysis products: cysteamine (2-aminoethanethiol) is measured by the absorbance of its fluoropyruvate adduct at 300 nm and pantothenate is measured by radioimmunoassay. Methods of [¹⁴C]pantethine synthesis are discussed and the labeled substrate employed in a third enzymatic assay. A fourth assay continuously monitors the absorbance of mercaptide ion at 240 nm. The mercaptide ion concentration increases proportionally with hydrolysis at a buffered pH because of a difference in pK(-SH) between pantetheine (9.9) and cysteamine (8.1) at 37°C. The enzyme shows a pH optimum of ca. 9 and an apparent K_m of 20 μm.     

A continuous spectrophotometric assay for the determination of cellulase solubilizing activity

A cellulase assay was developed for the continuous measurement of colored cellulose oligosaccharides (total carbohydrates) released during enzymatic hydrolysis of dyed crystal-line cellulose. Several cellulosic substrates were uniformly dyed by Remalzol brilliant blue R salt without altering their physical properties. Dyed Avicel (6.5%, w/w) was selected as the most representative substrate for the assay procedure. The assay was performed continuously in a simple, thermally controlled apparatus designed for filtration of the reaction mixture via a 5-μm-pore-size nylon filter to retain the crystalline dyed cellulose while spectrophotometrically monitoring the absorbance at 595 nm of the reaction filtrate. Crude supernatant cellulase of Trichoderma viride QM9414 was used to test the assay procedure. The activity of cellulase on dyed Avicel as measured by ΔA_595nm correlated directly with the total carbohydrates formed. The initial reaction rate of cellulase solubilizing activity was readily determined with high sensitivity. The continuous assay has utility for the study of cellulase kinetics and for the comparison of activities from different microorganisms.     

Determination of rifabutin in human plasma by high-performance liquid chromatography with ultraviolet detection

A simple, specific and sensitive high-performance liquid chromatographic (HPLC) method was developed for the determination of rifabutin in human plasma. Rifabutin and sulindac (internal standard) are extracted from human plasma using a C₈ Bond Elut extraction column. Methanol (1 ml) is used to elute the compounds. The methanol is dried down under nitrogen and reconstituted in 250 μl of mobile phase. Separation is achieved by HPLC on a Zorbax Rx C₈ column with a mobile phase composed of 0.05 M potassium dihydrogen phosphate and 0.05 M sodium acetate at pH 4.0-acetonitrile (53:47, v/v). Detection is by ultraviolet absorbance at 275 nm. The retention times of rifabutin and internal standard were approximately 10.8 and 6.9 min, respectively. The assay is linear over the concentration range of 5–600 ng/ml. The quantitation limit was 5 ng/ml. Both intra-day and inter-day accuracy and precision data showed good reproducibility.     

Structure-based engineering of glucose specificity in a family 10 xylanase from Streptomyces olivaceoviridis E-86

Substrate specificity is one of the most important functional property of enzymes. We use family 10 xylanase from Streptomyces olivaceoviridis as a model for substrate specificity of glycoside hydrolases. Seven variants were initially designed to change the preference from xylose to glucose at substrate binding subsites ?2 and ?1. The known mobility of Trp at the ?1 subsite and the influence of its environment, which is different in subset 1 and subset 2 family 10 enzymes, were taken into account in variant design. Q88A/R275A had the best ratio of p-nitrophenyl cellobioside vs p-nitrophenyl xylobioside hydrolyzing activity in the first series of variants. The crystal structure shows a movement of Trp274 compared to the native, as a result of loss of interaction with the long side chain of Arg275. The movement creates extra space for the hydroxymethyl of glucose, resulting in improved K_m on glucose derived substrates, while the negative effect on k_cat is compensated by the Q88A mutation, which also contributes to a further reduction of K_m. Further mutagenesis based on the Q88A/R275A variant resulted in 5.2 times improvement compared to the wild-type p-nitrophenyl cellobioside hydrolyzing activity, which is the best improvement obtained so far for an engineered xylanase.     

Determination of methylputrescine oxidase by high performance liquid chromatography

N-Methyl-Δ¹-pyrrolinium chloride, the product of the title enzyme, was synthesized by methylation of aminobutyraldehyde diethylacetal followed by acidic cleavage. After purification to homogeneity, it was characterized by NMR and UV spectroscopy. The compound had an absorption maximum at 210 nm; previous data indicating a maximum at 267 nm were shown to arise from an impurity. An HPLC method for the assay of N-methylputrescine oxidase from plant material was developed based on the separation of N-methyl-Δ¹-pyrrolinium chloride on a cation exchange column and direct detection at 210 nm. The enzyme activity was measured in the protein fraction extracted from plant roots and treated by gel filtration on disposable PD 10 columns. A K_m value of 1.9 mM was determined for methylputrescine and the enzyme from tobacco roots. The enzyme activities from N. tabacum and Datura stramonium were compared.     

Exploring the Energy Profile of Human IgG/Rat Anti-human IgG Interactions by Dynamic Force Spectroscopy

Interactions between antibody and antigen molecules play essential roles in biological recognition processes as well as medical diagnosis. Therefore, an understanding of the underlying mechanism of antibody?Cantigen interactions at the single molecular level would be beneficial. In the present study, human immunoglobulin (IgG) tethered cantilevers and rat anti-human IgG functionalized gold surfaces were fabricated by using self-assembled monolayers method. Dynamic force spectroscopy was employed to characterize the interactions between human (IgG) and rat anti-human IgG at the single-molecule level. The unbinding forces were determined to be 44.6?±?0.8, 65.8?±?3.0, 108.1?±?4.1, 131.1?±?11.2, 149.5?±?4.7, 239.5?±?3.1 and 294.7?±?7.7?pN with ramping loading rates of 514, 1,127, 3,058, 7,215, 15,286, 31,974 and 50,468?pN?s^-1, respectively. In addition, the unbinding forces were found to be increasing with the logarithm of apparent loading rates in a linear way. Fitting data group resulted in two distinct linear parts, suggesting there are two energy barriers. The corresponding distances in the bound and transition states (x _?? ) and the dissociation rates (K _off ) were calculated to be 0.129?±?0.006?nm, 3.986?±?0.162?s^?1 for the outer barrier and 0.034?±?0.001?nm, 36.754?±?0.084?s^?1 for the inner barrier. Such findings hold promise of screening novel drugs and discerning different unbinding modes of biological molecules.     

Effect of conformation and configuration of arabinose residues on the circular dichroism of C-glycosylflavones

Examination of a variety of arabinose containing C-glycosylflavones has shown that the sign and intensity of the CD band at 250–275 nm (charge-transfer band) reflect not only the point of attachment of the sugar to the flavone but also depend upon the absolute and anomeric configuration, ring-size and ring-conformation in addition to the preferred rotameric conformation of the sugar about the C-aryl, C-l″ bond. A change in stereochemistry of arabinose from the α to β anomer resulted in sign inversion of the 250–275 nm CD band for 6-C-l-arabinosylflavones. Furthermore, a 6-C-arabinosylflavone containing α-l-arabinose exhibited an oppositely signed charge-transfer CD band in comparison to one which contained α-d-arabinose. 6,8-Di-C-glycosylflavones containing arabinose and glucose exhibited CD bands resulting from contributions due to both sugars, if the arabinose was not present as the β-pyranose form (¹C₄, conformation).     

Polarographic assay for phospholipase A2

A rapid, specific, and quantitative assay for phospholipase A₂ from Naja naja venom has been devised, in which phospholipid hydrolysis is measured as soybean lipoxidase-catalyzed oxygen incorporation into the ensuing unsaturated fatty acids. Under conditions where phospholipid was limiting, a linear relationship developed between the extent of oxygen uptake and the amount of egg lecithin metabolized. When phospholipase was rate limiting, the initial rate of oxygen consumption was a linear function of phospholipase concentration over a 14-fold range from 30 to 420 ng/ml. This linear relationship did not exist at higher phospholipase levels, probably due to the micellar nature of the phospholipid. Since this assay can readily detect as little as 17 ng/ml of phospholipase A₂ (Naja naja venom) and is insensitive to most potential interfering materials, it should be useful in a variety of applications.     

A sensitive fluorometric assay for plasminogen, plasmin, and streptokinase

A rapid, convenient, and highly sensitive fluorometric assay for plasmin (P), plasminogen (Pg), and streptokinase (SK) as the activator complex (SK·P) is described. These assays are based on the measurement of the fluorescence of β-naphthol (βN) released from α-N-methyl α-N-tosyl-l-lysine β-naphthol ester (MTLNE) by the P present or generated during the assay. The rate of βN release may be followed by direct recording or determined subsequently, following termination of the enzyme reaction at a fixed digestion time, by the addition of p-nitrophenyl-p′-guanidinobenzoate. The latter method may be readily automated. The K_m and V values for the hydrolysis of MTLNE by P or SK·P are equivalent. The Pg activator activity of P was shown to be very small (less than 0.2% of that of SK·P).     

Screening for flavonol 3-glycoside specific β-glycosidases in plants using a spectrophotometric enzymatic assay

A simple and rapid spectrophotometric assay for following the hydrolysis of flavonol 3-glycosides has been developed. The assay profits from the fact that peroxidase converts flavonol aglycones to their corresponding 2,3-dihydroxyflavanones, producing a large shift in UV absorption, whereas flavonol 3-glycosides are not attacked. The amount of liberated aglycone can therefore be calculated from the decrease of flavonol absorption at 350–380 nm. A horseradish peroxidase-H₂O₂ test system can be used to investigate the hydrolysis of most flavonol 3-glycosides, whereas quercetin 3-glycosides can be tested using a peroxidase preparation from Mentha sp. which uses O₂ as cofactor rather than H₂O₂. Flavonol 3-glycoside synthesis, e.g. with UDP-sugars as cofactors, may also be tested by this particular system. Various plants and plant cell cultures were screened for kaempferol and quercetin 3-glycoside specific β-glycosidases. However, in no case could any specific activity be detected.     

Chromophoric peptide substrates for activity determination of animal aspartic proteinases in the presence of their zymogens: A novel assay

Solid-phase synthesis was used for the preparation of pyroglutamyl-histidyl-p-nitrophenylalanyl-phenylalanyl-alanyl-leucine amide (I) and glycyl-glycyl-histidyl-p-nitrophenylalanyl-phenylalanyl-alanyl-leucine amide (II), two water-soluble and sensitive chromophoric substrates of chicken pepsin, hog pepsin A, and bovine spleen cathepsin D. The kinetic constants of hydrolysis of the p-nitrophenylalanyl-phenylalanyl bond of the substrates were measured by difference spectrophotometry at 308 nm (Δ? = 860 m^?1 cm^?1) and by ninhydrin colorimetry (substrate I, ?₅₇₀ = 2.31 × 10⁴m^?1 cm^?1). The pH optimum of cleavage is 5 for the pepsins and 3.7 for cathepsin D. Since all three proteinases still have a significant activity at pH 5.5–6 a new, simple assay was designed for submicrogram quantities of pepsins in the presence of pepsinogens without interference of the latter. The method is particularly suitable for the analyses of the zymogen activation mixtures.     

Free-Labeled Nanogold Catalytic Detection of Trace UO 2 2+ Based on the Aptamer Reaction and Gold Particle Resonance Scattering Effect

In pH?5.5 2-(N-morpholino)-ethanosulfonic acid buffer solution containing 0.0125?M NaCl at 80?°C, the single-stranded substrate DNA hybrid with enzyme DNA to form double-stranded DNA (dDNA). The substrate chain of dDNA could be cracked catalytically by UO ₂ ²⁺ to produce a short single-stranded DNA (ssDNA) that adsorbed on the nanogold (NG) surface to form stable NGssDNA conjugate, and the unadsorbed NG take place aggregation to produce the NG aggregations in blue color. Both NG and NGssDNA exhibited strong catalytic activity on the gold particle reaction between HAuCl₄ and ascorbic acid that can be monitored by resonance scattering (RS) spectral technique at 620?nm. However, the catalytic effect of NG aggregation was very weak and it cannot be separated from the cracked reaction solution. When the UO ₂ ²⁺ concentration increased, the ssDNA increased, the NGssDNA increased, the formed gold particles increased, and the RS intensity at 620?nm increased. The increased RS intensity ??I _620?nm was linear to UO ₂ ²⁺ concentration in the range of 3.35?C23.45?pM, with a regression equation of ??I _620?nm?=?27.6C?+?29.1, and detection limit of 0.1?pM. This new RS assay was applied to analysis of UO ₂ ²⁺ in water sample with satisfactory results.