Cathepsin B2 measurement by sensitive fluorometric ammonia analysis

A procedure has been developed for the measurement of cathepsin B2 activity that is based upon highly sensitive fluorometric ammonia analysis. The fluorochrome results from the reaction of phthaldehyde and mercaptoethanol with ammonium salts at pH 7.4. The method is sensitive in the range of 5–400 nmoles ammonium salt/ml. The assay is highly specific for ammonia since amino acids, peptides, amines, and amides do not interfere. Likewise, other components of the cathepsin B2 reaction system do not interfere. The most distinct advantage of the method is that the awkward diffusion step of most routine ammonia analyses can be eliminated.     

Fluorometric analysis of amino sugars and derivatized neutral sugars

A rapid and sensitive procedure for the analysis of neutral and amino sugars is presented. Neutral sugars are separated after conversion to the corresponding glycamines, while the amino sugars are analyzed without modification, using an automatic amino acid analyzer and fluorometric detection. The method has been applied for the analysis of glycoproteins and oligosaccharides of the complex and high-mannose types.     

A fluorometric procedure for measuring the neuraminidase activity: its application to the determination of this activity in influenza and parainfluenza viruses

A fluorometric procedure for quantitating the amount of N-acetylneuraminic acid enzymatically released by the neuraminidase activity from N-acetylneuraminyl-lactose (sialyl-lactose) has been developed. The liberated lactose is hydrolyzed with beta-galactosidase, and the released galactose is oxidized with galactose dehydrogenase and NAD+; finally, the NADH produced is measured by fluorometry (excitation at 340 nm and analysis of emitted light at 465 nm). The fluorometric assay is about 10-fold more sensitive than the spectrophotometric procedure that measures NADH at 340 nm. It readily measures amounts as little as 2 nmol of sialic acid, and does not require the use of radioactive isotopes. Interferences due to sucrose or other substances, which cause errors in some cases with the use of the periodate-thiobarbiturate method for neuraminidase activity determination, are avoided. The procedure reported here provides a sensitive, rapid, and relatively simple method (feasible with commercialized reagents) for measuring the neuraminidase activity not only in purified samples from different sources but also directly in biological materials such as viruses. The technique has been tested with some viruses recently isolated belonging to Orthomyxoviridae or Paramyxoviridae families, known to be rich in neuraminidase. Reciprocally, this method can also be employed for determining the sialic acid concentration in acylneuraminyl-lactose-containing compounds when using purified neuraminidase for hydrolysis.     

A micromethod for the assay of aldose reductase, its application to pancreatic islets

A micromethod for the assay of aldose reductase is described. The method, which is based on the fluorometric measurement of the NADP+ formed when an aldose is converted to its corresponding polyol, was applied to lens and pancreatic islet crude homogenates, as well as semipurified lens aldose reductase. The fluorometric method has proved to be reproducible, more rapid, and more sensitive than the classical spectrophotometric procedure, and should find ready application in the screening of potential aldose reductase inhibitors.     

Molecular cloning and expression of the spsB gene encoding an essential type I signal peptidase from Staphylococcus aureus.

The gene, spsB, encoding a type I signal peptidase has been cloned from the gram-positive eubacterium Staphylococcus aureus. The gene encodes a protein of 191 amino acid residues with a calculated molecular mass of 21,692 Da. Comparison of the protein sequence with those of known type I signal peptidases indicates conservation of amino acid residues known to be important or essential for catalytic activity. The enzyme has been expressed to high levels in Escherichia coli and has been demonstrated to possess enzymatic activity against E. coli preproteins in vivo. Experiments whereby the spsB gene was transferred to a plasmid that is temperature sensitive for replication indicate that spsB is an essential gene. We identified an open reading frame immediately upstream of the spsB gene which encodes a type I signal peptidase homolog of 174 amino acid residues with a calculated molecular mass of 20,146 Da that is predicted to be devoid of catalytic activity.     

Peptide Utilization by Amino Acid Auxotrophs of Neurospora crassa

The ability of auxotrophs of Neurospora crassa to grow on certain tripeptides, despite the presence of excess competing amino acids, suggests it has an oligopeptide transport system. In general, dipeptides did not support growth except in those instances where extracellular hydrolysis occurred, or where the dipeptide appeared to be accumulated by an uptake system which is sensitive to inhibition by free amino acids. Considerable intracellular peptidase activity toward a large number of peptides was demonstrated, including a number of peptides which could not be utilized for growth. The intracellular peptidase activity was shown to be selective for amino acid composition and sequence (N-terminal or C-terminal) within the peptide; glycine-containing peptides were particularly poor substrates for peptidase activity. Only a small amount of extracellular peptidase activity could be detected.     

Assay for aliphatic amino acid decarboxylases by high-performance liquid chromatography

A sensitive and rapid assay for aliphatic amino acid decarboxylases based on separation of the product from the substrate by ion-pairing reversed-phase high-performance liquid chromatography and subsequent fluorometric detection has been developed. The resolution of substrates and products of seven amino acid decarboxylases, namely, arginine, aspartate, 2,6-diaminopimelate, histidine, glutamate, lysine, and ornithine decarboxylase, is complete within 15 to 35 min of isocratic elution. The limit of detection for the product is 40 pmol. The applicability of the procedure was assessed with glutamate decarboxylase. The formation of the product 4-aminobutyrate proved to be linear with time and protein concentration. The method allows the time course of the reaction to be followed in a single assay and works well with crude extracts of bacteria or tissues.     

A kinetic fluorometric assay of dipeptidyl peptidase IV in viable human blood mononuclear cells

A continuous-rate fluorometric assay of dipeptidyl peptidase IV (DP-IV) in viable human blood mononuclear cells using 7-(L-glycyl-L-prolylamido)-4-methylcoumarin as the substrate is described. The assay method is accurate, rapid, and highly sensitive for measuring the level of cell-surface bound DP-IV activity in suspension of blood mononuclear cells, as well as of other viable cells bearing this enzyme. We believe that the kinetic assay is suitable for studying the regulation of expression and the role of plasma membrane-bound DP-IV on the cellular level.     

A two-step purification of ATP-citrate lyase from rat liver and its use in a fluorometric assay for N-acetylglutamate synthetase

ATP-citrate lyase (EC 4.1.3.8) was purified to homogeneity from the liver of rats maintained on a diet containing no fat and high carbohydrate. The procedure involves two steps: dye-ligand chromatography on yellow MX-6G Sepharose CL-4B and ion-exchange chromatography on DEAE-Trisacryl. The specific activity of the enzyme was 10 mumol X min-1 X mg-1 at 25 degrees C, which is equal to the highest specific activity reported to date. The yield was also the highest reported to date, being in excess of 50%, and the enzyme isolated by this procedure has little proteolytic nicking. The pure enzyme was used to establish a coupled fluorometric assay for N-acetylglutamate synthetase (amino-acid acetyltransferase, EC 2.3.1.1) based on coupling coenzyme A production to the oxidation of NADH via ATP-citrate lyase and malate dehydrogenase. The method is easy to perform compared with existing methods and enables the measurement of 100 pmol X min-1 of N-acetylglutamate synthetase activity. The method is generally applicable for measurement of enzymes which produce coenzyme A. The fluorometric method was used to measure the Km for glutamate and acetyl coenzyme A at pH 7.0 and 25 degrees C, which were 8.2 and 0.4 mM, respectively. Arginine at 1 microM gave half-maximal activation of N-acetylglutamate synthetase.     

Inhibition of cathepsin B activity in human breast cancer tissue by cysteine peptidase inhibitor isolated from human placenta: immunohistochemical and biochemical studies

Cysteine peptidases and their endogenous inhibitors (CPI) have been shown to be involved in tumor progression and metastasis. Since their activity has been found to be changed in tumor tissue and/or body fluids of cancer patients, the determination of the peptidase/inhibitor levels is considered as a procedure of diagnostic value. Determination of cathepsin B, its precursor and inhibitor activity in homogenates of tumors and control breast tissue samples of patients with invasive ductal and lobular breast carcinoma and with benign breast disease (BBD) was performed using fluorometric assay. Immunohistochemical staining of the breast tissue samples was carried out using polyclonal antibody against cysteine peptidase inhibitor isolated from human placenta. Procathepsin B and cathepsin B were found to be significantly increased and their endogenous inhibitors decreased in homogenates of tumors from patients with breast cancer. A correlation between procathepsin B or cathepsin B activities as well as cysteine peptidase inhibitor activity and the histopathological grading of the tumor was observed. All samples of the tumor tissue showed positive immunostaining with antibody raised against cysteine peptidase inhibitor, while in the control tissue samples the immunostaining was much weaker. Significant difference observed between the activities of cathepsin B and/or its precursor in malignant and benign tumors might serve as a useful clinical indicator in discrimination between benign and invasive tumors.     

A sensitive high-performance liquid chromatographic-fluorometric assay for dihydrofolate reductase in adult rat brain, using 7,8-dihydrobiopterin as substrate

A liquid chromatographic-fluorometric assay has been developed to study the role of dihydrofolate reductase in adult rat brain since low levels of the enzyme preclude measurement by current spectrophotometric procedures. This method involves in vitro incubation of desalted, cell-free brain extracts with 7,8-dihydrobiopterin, NADPH, and an NADPH-regenerating system. The tetrahydrobiopterin formed is quantitatively converted to pterin using alkaline iodine oxidation, and the pterin formed is separated by liquid chromatography and detected fluorometrically. The method is linear from 100 fmol to greater than or equal to 1 nmol of product, and the sensitivity is at least 100 times greater than that of existing spectrophotometric assays. Enzyme activity of desalted brain extracts is linear with both time (to 100 min) and protein (from 50 to 620 micrograms). The enzyme shows an absolute requirement for NADPH, does not use NADH, and is completely inhibited by 10 nM methotrexate. The Km of the enzyme for NADPH was found to be 7.5 microM, while the Km for 7,8-dihydrobiopterin was 88 microM. Since brain dihydrobiopterin reductase has the same properties as dihydrofolate reductase, this fluorometric procedure can serve as a sensitive assay for dihydrofolate reductase.     

Determination of δ-aminolevulinate dehydratase activity by a specific fluorometric coupled-enzyme assay

A coupled-enzyme assay for the specific and sensitive determination of δ-aminolevulinate dehydratase activity has been developed. The assay specifically measured picomole quantities of the product, porphobilinogen, by its enzymatic conversion to uroporphyrinogen I and the fluorometric detection of oxidized uroporphyrin I. The coupled-enzyme assay was linear with time and protein concentration and required less than 3 h for 20 individual determinations. Under the standard assay conditions, 10 to 100 pmol of uroporphyrin I was reliably measured, representing 0.085 to 0.850 nmol/h of δ-aminolevulinate dehydratase activity per assay. In addition, the fluorometric assay was more sensitive than either the standard or the semimicro colorimetric methods. The specificity, rapidity, and sensitivity of this new fluorometric method facilitates the reliable determination of low levels of aminolevulinate dehydratase activity in small amounts of crude tissue homogenates or in cultured cells.     

Fluorometric assay for alcohol sulfotransferase

A sensitive fluorometric assay was developed for alcohol sulfotransferase (AST). This was the first continuous fluorometric assay reported for AST. It used 3'-phosphoadenosine 5'-phosphosulfate regenerated from 3-phosphoadenosine 5'-phosphate by a recombinant phenol sulfotransferase (PST) using 4-methylumbelliferyl sulfate as the sulfuryl group donor. The recombinant PST did not use the alcohol substrate under the designed condition, and the sensitivity for AST activity was found to be comparable to that of radioactive assay as reported in the literature. The change of fluorescence intensity of 4-methylumbelliferone corresponded directly to the amount of active AST and was sensitive enough to measure nanogram or picomole amounts of the enzyme activity. This fluorometric assay was used to determine the activities of AST as purified form and in crude extracts of pig liver, rat liver, and Escherichia coli. Some properties of human dehydroepiandrosterone sulfotransferase were determined by this method and were found to be comparable to published data. Under similar assay conditions, the contaminated activities of arylsulfatase in crude extracts were also determined. This method not only is useful for the routine and detailed kinetic study of this important class of enzymes but also has the potential for the development of a high-throughput procedure using microplate reader.     

Rapid assay to detect peptidases in column effluent fractions using -amino acid oxidase

A rapid, sensitive method to detect peptidase activity which utilizes an amino acid oxidase-coupled reaction adapted for microassay in wells of disposotrays is described. Susceptible amino acids in the presence of oxidase produce hydrogen peroxide, which combines with dianisidine to give a colored product. Immediately following column chromatography effluent fractions can be scanned simultaneously for peptidase activity toward several substrates. Color production enables direct visualization of relative rates of peptide cleavage as hydrolysis proceeds. This microassay enables one to simultaneously localize peptidases in effluent fractions following chromatography, gain information concerning substrate specificity of each peptidase eluted, and estimate the relative rates of hydrolysis of a given peptide by several enzymes.     

Rapid assay to detect peptidases in column effluent fractions using L-amino acid oxidase.

A rapid, sensitive method to detect peptidase activity which utilizes an amino acid oxidase-coupled reaction adapted for microassay in wells of disposotrays is described. Susceptible amino acids in the presence of oxidase produce hydrogen peroxide, which combines with dianisidine to give a colored product. Immediately following column chromatography effluent fractions can be scanned simultaneously for peptidase activity toward several substrates. Color production enables direct visualization of relative rates of peptide cleavage as hydrolysis proceeds. This microassay enables one to simultaneously localize peptidases in effluent fractions following chromatography, gain information concerning substrate specificity of each peptidase eluted, and estimate the relative rates of hydrolysis of a given peptide by several enzymes.     

Neuronal ceroid lipofuscinoses caused by defects in soluble lysosomal enzymes (CLN1 and CLN2)

Infantile and classical late infantile neuronal ceroid lipofuscinoses (NCL) are two recent additions to the expanding spectrum of lysosomal storage disorders caused by deficiencies in lysosomal hydrolases. They are latecomers to the lysosomal storage disorders, probably because of the heterogeneous nature of the storage material, which precluded meaningful biochemical analysis. Infantile NCL is caused by deficiency in palmitoyl-protein thioesterase, an enzyme that hydrolyzes fatty acids from cysteine residues in lipid-modified proteins. Classical late-infantile NCL is caused by a deficiency in tripeptidyl amino peptidase-I, a lysosomal peptidase that removes three amino acids from the free amino terminus of peptides or small proteins. Late-onset forms of these disorders have been described. The clinical, biochemical, and molecular genetic aspects of these two latest lysosomal storage disorders are discussed in this review. In addition, approaches to treatment and future directions for research are examined.     

Fluorometric method for the enzymatic determination of cholesterol

A fluorometric method for the enzymatic determination of cholesterol content has been developed using a novel fluorogenic H2O2 probe, Amplex Red. This assay is performed in a 96-well microplate, and it is a one-step method amenable to automated procedures. Using commercially available cholesterol, our assay allows detection of 5 pmol (2 ng) cholesterol per well, which is 100-fold more sensitive than published fluorometric and colorimetric methods. When applied to the measurement of cholesterol levels in serum and food samples, the Amplex Red-based method has been found more attractive since the oxidation product of the Amplex Red method has superior long wavelength spectra which are less susceptible to interference from the biological compounds.     

A Fluorometric Assay for Detection of Lysyl Oxidase Enzyme Activity in Biological Samples

Lysyl oxidase catalyzes the final known enzymatic step required for collagen and elastin cross-linking in the biosynthesis of normal mature functional insoluble extracellular matrices. In addition, lysyl oxidase has been identified as a possible tumor suppressor. Lysyl oxidase activity in biological samples is traditionally and most reliably assessed by tritium release end-point assays using radiolabeled collagen or elastin substrates involving laborious vacuum distillation of the released tritiated water. In addition, a less sensitive fluorometric method exists that employs nonpeptidyl amine lysyl oxidase substrates and measures hydrogen peroxide production with horseradish peroxidase coupled to homovanillate oxidation. The present study describes a more sensitive fluorescent assay for lysyl oxidase activity that utilizes 1,5-diaminopentane as substrate, and released hydrogen peroxide is detected using Amplex red in horseradish peroxidase-coupled reactions. This method allows the detection of 40 ng of enzyme per 2 ml assay at 37 degrees C and is 7.5 times more sensitive than the currently available fluorometric assay for enzyme activity. This method eliminates the interference that occurs in some biological samples and can be successfully used to detect lysyl oxidase activity in cell culture experiments.     

A fluorometric assay for peptidyl alpha-amidation activity using high-performance liquid chromatography

A rapid and sensitive method for the determination of peptidyl alpha-amidation activity has been developed and is based on reverse-phase high-performance liquid chromatographic separation and fluorometric detection. A dansylated tripeptide, N-dansyl-Tyr-Val-Gly-OH, is used as the substrate in the assay and the amount of alpha-amidation activity is determined by quantitating the extent of its conversion to product, N-dansyl-Tyr-Val-NH2. Both product and substrate can be detected in a single assay in quantities as low as 5 fmol by isocratic elution using C-18 reverse-phase columns. The method yields highly reproducible results and requires less than 3 min per sample for separation and quantitation. The assay procedure is applicable to the screening of a large number of samples under different pH conditions and is readily adaptable for use in a variety of studies. For example, the procedure is ideal for detecting alpha-amidation activity in various tissues, monitoring activity at the different stages during purification of a particular alpha-amidation enzyme, determining kinetic parameters of the purified enzyme, and identifying both competitive and noncompetitive inhibitors.     

Use of fluorescamine in the chromatographic analysis of peptides from proteins

A routine procedure for the fluorometric analyses of peptides in the column chromatographic fraction has been described. Sensitivities of detection are 3–5 times higher in the direct fluorescamine method and 6–50 times higher in the method with alkaline hydrolysis than the conventional ninhydrin color method with hydrolysis (11).Reactivity of peptides with fluorescamine appears to depend mainly on the nature of amino acids occupying the amino termini; ?-amino groups of lysine residues in the peptides tested have been found not to contribute significantly in yielding fluorescence in the reaction.