[ANSA analysis. III. Synthesis of aminonaphthalinesulfonamide chromogenic substrates for protease analysis]

A review of synthetic methods of peptide substrates containing aminonaphthalenesulphonamide (ANSA) as the detected leaving group is presented. Variations of aminoacylic and peptide ANSA derivatives using ANSA as the C-protect group at all stages of the peptide synthesis, condensations of the ANSA with the N-protected peptide fragment obtained preliminary, the application of aminoacyl-ANSA as syntones are discussed. The synthesis scheme used while determining optimal ANSA substrates that involves reactions of aminoacyl derivatives of aminonaphthalenesulfonylchlorides with amines is shown. The application of di-tert-butylpyrocarbonate, DCC, chlorodimethylformiminium chloride, alkylchloroformate as condensing agents is described. The protection of amino groups was carried out by using Boc- and Cbz- groups.

New reagent for colorimetric assay of calcium in serum

We report a new single-reagent colorimetric assay for the determination of calcium in serum. The assay is based on a novel chromogenic tetracarboxylic acid chelating agent. The method has several advantages over the o-cresolphthalein complexone (CPC) method, including improved linearity, better accuracy, increased stability, and lower working pH (9.0). The calibration curve for the assay is linear up to 4 mmol/L. The results for 47 patients' samples correlated well with results obtained with an Instrumentation Laboratory atomic absorption spectrophotometer. The mean (+/- SD) calcium values for the new method were 2.27 +/- 0.06 mmol/L and 2.26 +/- 0.05 mmol/L for the comparison method. The on-system stability of the reagents is 1 week vs 8 h for the CPC method.

X-Neu5Ac: a novel substrate for chromogenic assay of neuraminidase activity in bacterial expression systems

A chromogenic substrate 1, 5-bromo-4-chloroindol-3-yl 5-acetamido-3,5-dideoxy-alpha-D-glycero-D-galacto-2-nonulopyranosidon ic acid (X-Neu5Ac), has been synthesized to facilitate the screening of bacterial colonies or plaques for the detection of either natural or mutant neuraminidase activity. Substrate 1 was hydrolyzed by neuraminidase isolated from Clostridium perfringens to release a halogenated indol-3-ol 2 that undergoes rapid aerobic oxidation to form the dark blue pigment, 5,5'-dibromo-4,-4'-dichloroindigo 3. Preliminary kinetic studies indicate that this compound is a good substrate (Km 0.89 x 10(-3) M) for neuraminidase and is quite stable under identical conditions in the absence of enzyme. These results suggest that X-Neu5Ac 1 can be useful to screen for bacterially-encoded enzyme production directly on agar plates.

Syntheses of modified 2-chloro-4-nitrophenyl beta-maltopentaosides as useful substrates for assay of human alpha amylase

Twenty-three novel 2-chloro-4-nitrophenyl beta-D-maltopentaosides modified at the 6(5) and/or 4(5) position were synthesized as substrates for human alpha amylase. Two human alpha amylases hydrolyzed 6(5)-deoxy-6(5)-, 6(5)-O-, and 4(5),6(5)-di-O-substituted derivatives at essentially a single D-glucosidic linkage, but 4(5),6(5)-O-bridged and 4(5)-O-substituted derivatives were hydrolyzed at two or more linkages. The amylases displayed smaller Km values for the compounds having hydrophobic modifications. In these derivatives, 2-chloro-4-nitrophenyl O-(6-bromo-6-deoxy-alpha-D-glucopyranosyl)-(1-->4)-tris[O-alpha-D- glucopyranosyl-(1-->4)]-beta-D-glucopyranoside (10), 2-chloro-4-nitrophenyl O-(6-azido-6-deoxy-alpha-D-glucopyranosyl)-(1-->4)- tris[O-alpha-D-glucopyranosyl-(1-->4)]-beta-D-glucopyranoside (19), and 2-chloro-4-nitrophenyl O-[6-O-(N-isopropyl)carbamoyl-alpha-D-glucopyranosyl]-(1-->4)- tris[O-alpha-D-glucopyranosyl-(1-->4)]-beta-D-glucopyranoside (30), which were rapidly hydrolyzed by the two amylases at a limited position at an approximately equal rate, were shown to be very useful blocked-type substrates for assay of human alpha amylase.

Mechanistic investigation of medium-chain fatty acyl-CoA dehydrogenase utilizing 3-indolepropionyl/acryloyl-CoA as chromophoric substrate analogues

The CoA derivative 3-indolepropionyl-CoA (IPCoA) serves as a competent pseudosubstrate for the medium-chain fatty acyl-CoA dehydrogenase (MCAD)-catalyzed reaction. The reaction product trans-3-indoleacryloyl-CoA (IACoA) exhibits a characteristic UV-vis absorption spectrum with lambda max = 367 nm and epsilon 367 = 26,500 M-1 cm-1. The chromophoric nature of IACoA allows us to measure the direct conversion of substrate to product (at 367 nm) without recourse to absorption signals for either the enzyme-bound flavin or the coupling electron acceptors, as well as probe the enzyme site environment. The interaction of IACoA with medium chain fatty acyl-CoA dehydrogenase (MCAD)-FAD is characterized by resultant (spectra of the mixture minus the individual components) absorption peaks at 490, 417, and 355 nm. These absorption peaks increase in magnitude as the pH of the buffer media decreases. Transient kinetic analysis for the interaction of MCAD-FAD with IACoA suggests that the formation of the enzyme-IACoA complex proceeds in two steps. The first (fast) step involves the formation of an E-IACoA collision complex, which [formula: see text] is isomerized (concomitant with changes in the protein structure) to an E*-IACoA complex in the second (slow) step. We have studied the effect of pH on Kc, k2, and k-2. While Kc shows practically no dependence on pH (within a 2-fold variation between pH 6.0 and 9.5), k2 and k-2 show a strong dependence on pH. Both k2 and k-2 exhibit a sigmoidal dependence on the pH of the buffer media, with pKa's of 7.53 and 8.30, respectively. In accordance with the model presented herein, the pKa of 7.53 represents an enzyme site group which is involved in the interaction with IACoA within the E-IACoA collision complex. This pKa is perturbed to 8.30 upon isomerization of the collision complex. The pH-dependent changes in k2 and k-2 are such that the equilibrium distribution between E-IACoA and E*-IACoA is favored to the latter complex (by about 20-fold) at lower pH than at higher pH. A cumulative account of the spectral, kinetic, and thermodynamic properties of the enzyme-IACoA complexes has allowed us delineate the microscopic pathway by which the E-IACoA isomerization (presumably via protein conformational changes) is coupled to the proton equilibration steps.

A chromogenic substrate for phosphatidylinositol-specific phospholipase C: 4-nitrophenyl myo-inositol-1-phosphate

A chromogenic water-soluble substrate for phosphatidylinositol-specific phospholipase C was synthesized starting from myo-inositol employing isopropylidene and 4-methoxytetrahydropyranyl protecting groups. In this analogue of phosphatidylinositol, 4-nitrophenol replaces the diacylglycerol moiety, resulting in synthetic, racemic 4-nitrophenyl myo-inositol-1-phosphate. Using this synthetic substrate a rapid, convenient and sensitive spectrophotometric assay for the phosphatidylinositol-specific phospholipase C from Bacillus cereus was developed. Initial rates of the cleavage of the nitrophenol substrate were linear with time and the amount of enzyme used. At pH 7.0, specific activities for the B. cereus enzyme were 77 and 150 mumol substrate cleaved min-1 (mg protein)-1 at substrate concentrations of 1 and 2 mM, respectively. Under these conditions, less than 50 ng quantities of enzyme were easily detected. The chromogenic substrate was stable during long term storage (6 months) as a solid at -20 degrees C.

Sensitive, soluble chromogenic substrates for HIV-1 proteinase

By replacement of the P1' residue in a capsid/nucleocapsid cleavage site mimic with 4-NO2-phenylalanine (Nph), an excellent chromogenic substrate, Lys-Ala-Arg-Val-Leu*Nph-Glu-Ala-Met, for HIV-1 proteinase (kappa cat = 20 s-1, Km = 22 microM) has been prepared. Substitution of the Leu residue in P1 with norleucine, Met, Phe, or Tyr had minimal effects on the kinetic parameters (kappa cat and kappa cat/Km) determined at different pH values, whereas peptides containing Ile or Val in P1 were hydrolyzed extremely slowly. The spectrophotometric assay has been used to characterize the proteinase further with respect to pH dependence, ionic strength dependence, and the effect of competitive inhibitors of various types.

The chemical synthesis of the chromogenic substrates, H-D-Val-L-Leu-L-Lys-p-nitroanilide (S2251) and H-D-Ile-L-Pro-L-ARG-p-nitroanilide (S2288)

We describe detailed procedures for the chemical synthesis of two costly chromogenic substrates, H-D-Ile-L-Pro-L-Arg-p-nitroanilide (S2288) and H-D-Val-L-Leu-L-Lys-p-nitroanilide (S2251), which are widely employed for assay of tissue plasminogen activator and plasmin, respectively, as well as in inhibitor assays for these enzymes. Quantities of 5 grams or more of these reagents can be synthesized on a bench-top scale with routine equipment in a laboratory or facility with minimal experience in peptide chemistry. While some of the chemical reactions have been employed previously, improvements have been made therein in this manuscript, and these detailed descriptions are mainly provided to be of service to investigators who employ large quantities of these substrates in their work. The main strategic difference between our methodology and that employed previously is the coupling of the L-Lys- and L-Arg-p-nitroanilides to the previously synthesized, and otherwise completed peptides, which gives superior yields of final product and provides flexibility the chemical synthesis of substrates with other amino acids present.

Chromophoric and fluorophoric peptide substrates cleaved through the dipeptidyl carboxypeptidase activity of cathepsin B

The action of bovine spleen cathepsin B as a dipeptidyl carboxypeptidase on newly synthesized substrates of the type peptidyl-X-p-nitrophenylalanyl (Phe(NO2))-Y (X,Y = amino acid residue) or 5-dimethylaminonaphthalene-1-sulfonyl (Dns)-peptidyl-X-Phe(NO2)-Y was investigated. The kinetic parameters of hydrolysis of the X-Phe(NO2) bond were determined by difference spectrophotometry (delta epsilon 310 = 1600 M-1 cm-1) or by spectrofluorometry by following the five- to eightfold increase of Dns-group fluorescence with excitation at 350 nm and emission at 535 nm. The substrates were moderately sensitive to cathepsin B; kcat varied from 0.7 to 4 s-1 at pH 5 and 25 degrees C; Km varied from 6 to 240 microM. The very acidic optima of pH 4-5 are characteristic for dipeptidyl carboxypeptidase activity of cathepsin B. Bovine spleen cathepsins S and H had little and no activity, respectively, when assayed with Pro-Glu-Ala-Phe(NO2)-Gly. These peptides should be a valuable tool for routine assays and for mechanistic studies on cathepsin B.

10-Acetyl-10-hydroxyxantho[2,3-f]tetralin 8-glycosides as angular chromophore analogues of anthracyclines: synthesis, redox properties, microsomal oxygen consumption, and antileukemic evaluation

10-Acetyl-7,8-dihydroxyxantho[2,3-f]tetralin is obtained by photo-Fries rearrangement of an acylated and double ketal protected tetralin followed by sodium thiocresylate catalyzed rearrangement of the resulting benzoyltetralin. Introduction of the 10-hydroxy function with base, triethyl phosphite, and molecular oxygen affords six products. These include the desired epimeric 10-acetyl-7,8,10-trihydroxyxantho[2,3-f]tetralins in addition to products resulting from novel valence tautomerism and cycloreversion reactions in the oxidation reaction. Glycosidic coupling to the fully functionalized cis-8,10-dihydroxy epimer of the aglycon to protected chlorodaunosamine by a modified Koenigs-Knorr method proceeded satisfactorily. By contrast the epimeric trans-8,10-dihydroxy compound failed to undergo coupling under these conditions. This is attributed to facile competing intramolecular hemiketal formation in the latter case. The new angular glycosides are very resistant to electrochemical reduction and display very low (3-10%) augmentation of hepatic microsomal oxygen consumption relative to doxorubicin. The observed, albeit low, cytotoxicity against leukemia L1210 in cell culture provides an additional example where the presence of the quinone moiety in the parent anthracyclines, which is implicated in the clinical cardiotoxicity, may not be necessary for the expression of anticancer properties.

Determination of leucine aminopeptidase using phenylalanyl-3-thia-phenylalanine as substrate

The peptide mimetic L-phenylalanyl-L-3-thiaphenylalanine has been shown to facilitate a sensitive and simple determination of leucine aminopeptidase. A colorimetric assay, employing Ellman's reagent to detect the thiophenol released upon hydrolysis of the dipeptide, has been developed. Under the experimental conditions employed the substrate has a Km of 0.054 mM and a kcat of 5800 min-1 and can distinguish sharply between leucine aminopeptidase and aminopeptidase M.

Sphingomyelinases and Niemann-Pick disease

In the first part the properties of normal mammalian sphingomyelinases are reviewed: The lysosomal acid sphingomyelinase is a polymeric glycoprotein (subunit Mr between 28 000 and 70 000) which hydrolyses natural sphingomyelin, coloured and fluorescent semi-synthetic analogues (trinitrophenyl-aminolauryl-sphingomyelin and pyrenedecanoyl-sphingomyelin) and the synthetic analogue 2-N-hexadecanoylamido-nitrophenyl-phosphorylcholine. The suitability of these substrates and of synthetic fluorescent derivatives of methylumbelliferone is discussed. The effect of lipids, detergents and other effectors on the enzyme activity is also described. The neutral sphingomyelinase from brain tissue, localized in cell membranes, has a high Mr (160 000 and 600 000), is heat labile, hydrolyses sphingomyelin and its coloured and fluorescent analogues, but not 2-N-hexadecanoylamido-nitrophenyl-phosphorylcholine. A new method is available for determining enzyme activity in the intact cell through the utilization of endogenous or exogenous sphingomyelin as substrate. In the second part of the review, the classification of Niemann-Pick disease, the characteristic features of each type and the biological tools used for the diagnosis are reported. Experimental models (animal models and cellular models in culture) are reviewed with a particular attention to a new model system, Epstein-Barr virus-transformed lymphoid cell lines.

[A new fluorogenic substrate for human galactocerebroside-beta-D-galactosidase]

A new fluorogenic compound--6-hexadecanoylamino-4-methyl-umbelliferyl-beta-D-gala cto pyranoside (HMGal), a substrate for human galactocerebroside beta-D-galactosidase (HG), has been synthesized. A method for determining the HG activity based on the use of HMGal as a fluorogenic substrate has been developed. The specificity of HMGal hydrolysis by HG has been demonstrated in experiments with enzyme preparations from human skin fibroblasts and leukocytes in normally and in hereditary glycolipidosis (GM1-gangliosidosis and Krabbe's disease). The use of HMGal permits to markedly increase the sensitivity of the method used for determining the HG activity.

Soluble chromogenic substrates for the assay of endo-1,4-beta-xylanases and endo-1,4-beta-glucanases

New soluble chromogenic substrates were prepared for specific and rapid assays of endo-1,4-beta-xylanases and endo-1,4-beta-glucanases. A soluble beechwood 4-O-methyl-D-glucurono-D-xylan was dyed with Remazol brilliant blue R, and hydroxyethylcellulose was coupled to Ostazin brilliant red H-3B. The assays are based on photometric measurements of the enzyme-released dyed fragments soluble in the presence of organic solvents which precipitate the original substrates and their high-molecular-weight fractions. The assays are advantageous for rapid analyses of large amount of samples and also permit evaluation of the activities of both enzymes in the presence of exo-beta-glycanases and beta-glycosidases, at a high level of reducing compounds and viable cells, on the cell surface and on cell membranes and organelles.

The synthesis, purification, and evaluation of a chromophoric substrate for pepsin and other aspartyl proteases: design of a substrate based on subsite preferences

A convenient chromophoric assay for porcine pepsin has been developed using a new synthetic substrate. The sequence of this substrate was chosen based on the known subsite preferences for this enzyme. The peptide contains a phenylalanyl-p-nitrophenylalanine sequence at the reactive site. Cleavage of this bond yields a change in absorbance at 310 nm of between 1700 and 2000 per mole. This allows kinetic data to be obtained readily and accurately. The products of cleavage have been identified by isolation of a peptide fragment by high-performance liquid chromatography. Values of kcat, Km, and kcat/Km of 94 +/- 6 s-1, 0.13 +/- .04 mM, and 815 +/- 210 s-1/mM-1 were obtained at pH 3.0 and 37 degrees C. The peptide is soluble over the pH range from 2 to 7, thus facilitating determination of the pH dependence of the kinetic parameters. The substrate is also valuable in studying the inhibition of pepsin.

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 (delta epsilon = 860 M-1 cm-1) and by ninhydrin colorimetry (substrate I, epsilon 570 = 2.31 X 10(4) M-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.

Fluorogenic substrates for bacterial aminopeptidase P and its analogs detected in human serum and calf lung

A sensitive fluorimetric assay was developed for bacterial aminopeptidase P, based on intramolecularly quenched fluorogenic substrates. Two substrates were synthesized. Phe(NO2)-Pro-HN-CH2-CH2-NH-ABz (substrate I) and Phe(NO2)-Pro-Pro-HN-CH2-CH2-NH-ABz (substrate II), in which the Phe(NO2) group (rho-nitro-L-phenylalanyl) quenches the fluorescence of the ABz group (omicron-aminobenzoyl). Both substrates were readily cleaved by aminopeptidase P from Escherichia coli, releasing rho-nitro-L-phenylalanine and causing a proportional increase in fluorescence. Complete hydrolysis of the two substrates resulted in a 7.5-fold and 3.4-fold fluorescence increase, respectively. Applying this fluorogenic assay, we were able to detect and measure quantitatively amino-peptidase P-like activity in the human serum and calf-lung extracts. Substrate II was shown to be specifically cleaved by aminopeptidase P in these preparations, while substrate I was apparently cleaved by other enzymes as well. In both preparations, the enzyme activity was independent of Co2+ ions, and Pro-HN-CH2-CH2-NH-ABz (Cbz) was inhibitory. The kinetic constant Km was determined as 0.35 mM and 0.28 mM for the human serum and the calf-lung enzymes respectively. The enzyme activity was only slightly dependent on pH in the range 7.0-8.4.

A new chromogenic substrate for angiotensin-converting enzyme

The compound para-nitrobenzyloxycarbonylglycyl-(S-4-nitrobenzo-2-oxa- 1,3-diazole)-L-cysteinylglycine [NO2ZGly(S-NBD)CysGly] with an absorption maximum at 423 nm is readily hydrolyzed by angiotensin-converting enzyme (EC 3.4.15.1. peptidlyldipeptide hydrolase) to yield the S-benzfurazan derivative of cysteinylglycine. An internal S-->N shift occurs immediately to yield the N-benzfurazan derivative which in turn reacts with the sulfhydryl reagent 4,4'-dithiodipyridine to produce the mixed disulfide with an intense absorption at 461 nm. The maximum difference in molar absorptivity of 13,000 M-1 cm-1 occurs at 470 nm.