Inhibition of ribonucleotide reductase by antitumor agents related to levodopa and dopamine

Using partially purified enzyme from L1210 cells, dihydroxybenzene derivatives related structurally to dopamine were shown to reversibly inactivate ribonucleotide reductase. A structure-activity analysis revealed that derivatives with side-chains, which contain a negatively-charged group, had significantly reduced inhibitory activity. The ability of these compounds to inhibit ribonucleotide reductase was dependent on the hydroxyl groups being in the ortho position and did not correlate with free radical inhibitory activity. A kinetic analysis by the method of Lineweaver-Burk indicated that the inhibition of ribonucleotide reductase by the derivative 3,4-dihydroxybenzylamine was competitive with the reducing substrate dithioerythritol. This analog, in combination with hydroxyurea, gave synergistic inhibition or ribonucleotide reductase, suggesting different sites of action. Using Tween 80-treated L1210 cells, it was found that these drugs had an immediate inhibitory effect on ribonucleotide reductase activity in intact, reversibly permeabilized cells. Furthermore, although these drugs had no immediate effect on DNA polymerase, in permeabilized L1210 cells (when the cells were preincubated with the dihydroxybenzene derivatives for 1 hr prior to permeabilization), there was significant inhibition of DNA polymerase activity. The two key enzymes for DNA synthesis appear to be sequentially inhibited by these analogs, with the reduced form (quinol) inhibiting ribonucleotide reductase and the oxidized form (quinone) inhibiting DNA polymerase.

Isolation and characterization of a 115,000-dalton matrix-associated glycoprotein from chick aorta

Chick aortas were extracted sequentially with phosphate-buffered saline, 6 M guanidine HCl, and 6 M guanidine HCl containing dithioerythritol. The proteins present in the guanidine HCl + dithioerythritol extract were separated by DEAE-cellulose chromatography, and the fractions recovered were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Five major glycoprotein components with apparent Mr = 205,000, 195,000, 150,000, 135,000, and 115,000 (gp 115) were identified. gp 115 was further studied since it was the only noncollagenous protein based on amino acid analysis. The protein was purified to homogeneity by preparative electrophoresis. Its amino acid composition was characterized by a high content of glutamic acid and arginine and a relatively high content of leucine, glycine, and alanine. The concentration of gp 115 in the guanidine HCl + dithioerythritol extract was about 15-fold that in the guanidine and saline extracts. Overall, about 80% of the protein was solubilized with guanidine HCl + dithioerythritol, suggesting that most of it formed large aggregates stabilized by disulfide bonds in vivo. Immunofluorescence studies with specific antibodies showed that gp 115 formed an extracellular fibrillar network in the aorta wall. One-dimensional finger printing with Staphylococcus aureus V8 protease and immunological studies indicated that the protein was unrelated to fibronectin and laminin. The data led us to conclude that gp 115 is a novel extracellular component of chick aorta.

Analyses of human tracheobronchial mucus from healthy subjects

Tracheobronchial mucus was obtained from four healthy subjects by fibreoptic bronchoscopy. The material was fractionated by gel exclusion chromatography on a Sepharose CL2B column. One peak of optical density 280 nm was found in the excluded volume and another in the included volume suggesting that these contained the majority of the aromatic amino acids. Alcian Blue was used to precipitate acidic glycoproteins in each fraction. When the dye had been redissolved two peaks of optical density at 620 nm were detected, in the excluded and included volumes respectively, and these peaks corresponded with the absorbance at 280 nm. The elution profiles were similar to those given by mucins from other systems. Treatment with urea and dithiothreitol caused no change in the elution profile so there is no evidence that disulphide bonds link glycoprotein subunits in airway mucus from healthy subjects.

Kinetic correlations between the disulfide bond reduction and the induced conformational change of proteins

Kinetic correlations between the disulfide bond reduction in excess dithioerythritol and the induced conformational change were studied on two proteins, bovine alpha-lactalbumin and soybean trypsin inhibitor, at 25 degrees C and pH 8.0-8.5 by measuring the absorbance of oxidized dithioerythritol at 310 nm and the ellipticity at 270 nm, respectively. With alpha-lactalbumin, in the absence of guanidine hydrochloride (Gdn x HCl) or in dilute Gdn x HCl, the kinetics for the bond reduction and the conformational change were both of a biphasic type. The fast phase was complete within a few seconds and was associated with the reduction of some of the disulfide bonds and with almost complete loss of the tertiary structure. The slow phase was associated with the reduction of other disulfide bonds. In concentrated Gdn x HCl, the kinetics of both processes were observed as a single phase, the rate of which was similar to that of the slow phase in the absence of Gdn x HCl or in dilute Gdn x HCl. In all cases studied, the rate of the bond reduction was similar to that of the conformational change induced. By correcting the change in absorbance at 310 nm to a contribution from the protein due to the conformational change, the number of bonds which are reduced in the fast phase in the absence of Gdn x HCl was determined to be 1.0-1.1. It was shown, taking observations of others and theoretical results into account, that the bond reduced in the fast phase might be the one between Cys 6 and Cys 120. On the other hand, on of two bonds of soybean trypsin inhibitor in the native form was reduced in the fast phase without any loss of the tertiary structure, and the other was reduced in the slow phase. Considering the results of other researchers, it was concluded that the bond reduced in the fast phase of the inhibitor is a 136-145 bond.

The effect of thiol compounds on the autolysis of papain

Incubation of papain with 3--17.5 mM dithiothreitol and dithioerythritol at pH 8.5 causes inactivation owing to autolysis. Such inactivation is not observed on incubation with equivalent concentrations of mercaptoethanol, cysteine or 2,3-dimercaptopropanol. The inactivation rate is independent of papain concentration within the range of 0.5--2% and is proportional to dithiothreitol concentration. This is in agreement with a sequence of two reactions: (Formula: see text) the first reaction being rate-limiting. S-Carboxymethyl-papain (I) and S-carboxamidomethyl-papain (II) were incubated with 18 mM dithiothreitol at pH 8.5 and, after stopping the reaction with iodoacetic acid, were subjected to gel electrophoresis. Electrophoretograms of both I and II exhibited a small new band attributable to a species with one disulphide bond reduced and carboxymethylated. The new band on II was more pronounced than that of I. It is argued that (Formula: see text) is a papain species with one reduced disulphide bond, sensitive to proteolytic attack by native papain.

[Disintegration of human spermatozoa in flow cytometry of semen]

In some cases, the pretreatment of human spermatozoa produced desintegration of various degrees, while in others a reduced staining was observed. For the evaluation of these phenomena the following techniques were applied: papain/DTE solution at pH 5.5 and 6.4, pepsin solution and a staining procedure without any preceeding decondensation of the spermatozoa nuclei. Pathological spermatozoa from patients with severe disorders of spermatogenesis showed an extended resistance to the pretreatment procedures, the spermatozoa being stained after papain/DTE pretreatment at pH 5.5 only. Contrary to this finding, normal spermatozoa and spermatozoa with slight morphological aberrations desintegrated when papain/DTE solutions were used. In this group the abortion rate was high.

Antioxidants in purification, stabilization, and formulation of the antineoplastic agent 6-selenoguanosine

6-Selenoguanosine (NSC 137679) was stablized and formulated as a lyophilized parenteral paroduct using ascorbic acid as an antioxidant. In addition to preventing the oxidation of 6-selenoguanosine to the corresponding diselenide in aqueous solution, ascorbic acid reduced the diselenide already in the bulk drug. Dithioerythritol and sodium bisulfite also were evaluated as antioxidants. Dithioerythritol had effects similar to ascorbic acid, while sodium bisulfite reacted rapidly with 6-selenoguanosine.

Creatine kinase measurement in the 1977 CAP Enzymology Survey: anomalies explained

In the recently published results of the 1977 College of American Pathologists Enzymology Survey, Some anomalous results were obtained in measuring the creatine kinase (EC 2.7.3.2) activity of the samples. The cause of these anomalies was discovered to be an arginine kinase (EC 2.7.3.3) contaminant in one of the enzyme pools used to make the samples. The contaminant shows cross reactivity with creatine phosphate and is activated by dithioerythritol but not the other commonly used thiol activators.

Dithiols simulate endotoxin in the Limulus reaction

Dithiothreitol, dithioerythritol and bacterial lipopolysaccharides increase optical absorbance and clot Limulus lysate. Purification of dithiothreitol from possible endotoxin contamination by vacuum sublimation or chromatography does not abolish the reaction with lysate. The dithiols reported active here represent the smallest molecules capable of simulating endotoxin in the Limulus test.

The presence of two (Na+ + K+)-ATPase inhibitors in equine muscle ATP: vanadate nad a dithioerythritol-dependent inhibitor

A potent inhibitor of (Na+ + K+)-ATPase activity was purified from Sigma equine muscle ATP by cation- and anion-exchange chromatography. The isolated inhibitor was identified by atomic absorption spectroscopy and proton resonance spectroscopy to be an inorganic vanadate. The isolated vanadate and a solution of V2O5 inhibit sarcolemma (Na+ + K+)-ATPase with an I50 of 1 micrometer in the presence of 1 mM ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA), 145 mM NaCl, 6mM MgCl2, 15 mM KCl and 2 mM synthetic ATP. The potency of the isolated vanadate is increased by free Mg2+. The inhibition is half maximally reversed by 250 micrometer epinephrine. Equine muscle ATP was also found to contain a second (Na+ + K+)-ATPase inhibitor which depends on the sulfhydryl-reducing agent dithioerythritol for inhibition. This unknown inhibitor does not depend on free Mg2+ and is half maximally reversed by 2 micrometer epinephrine. Prolonged storage or freeze-thawing of enzyme preparations decreases the susceptibility of the (Na+ + K+)-ATPase to this inhibitor. The adrenergic blocking agents, propranolol and phentolamine, do not block the catecholamine reactivation. The inhibitors in equine muscle ATP also inhibit highly purified (Na+ + K+)-ATPase from shark rectal gland and eel electroplax. The inhibitors in equine muscle ATP have no effect on the other sarcolemmal ATPases, Mg2+-ATPase, Ca2+-ATPase and (Ca2+ + Mg2+)-ATPase.

Studies on the structure and immunological activity of carcinoembryonic antigen - the role of disulphide bonds

Carcinoembryonic antigen (CEA) has been shown to contain no free cysteine thiol groups but 6 cystine disulphide bonds. 5'5-Dithiobis-(2-nitrobenzoic acid) (DTNB) will react with CEA only after reduction of the disulphide bonds with dithioerythritol. Reduction-alkylation of CEA using dithioerythritol and bromo-[1-14C] acetic acid confirmed the presence of 6 disulphide bonds, as did oxidation of the glycoprotein with performic acid. The products from the DTNB and reduction-alkylation treatments of CEA had less capacity to inhibit the binding of [125I]-CEA to anti-CEA in a radioimmunoassay than the original CEA but could, in sufficient quantities, totally inhibit the binding. Removal, using mercaptoethanol, of the thiol blocking groups from the DTNB-treated CEA resulted in a 55% recovery of antigenic activity. The product from the performic acid oxidation could only inhibit approximately 50% of the binding. Treatment of CEA with 0.533M sodium periodate (NaIO4) greatly reduced its antigenic activity, presumably a result of the oxidative cleavage of the disulphide bonds. No loss in activity, however, was observed when 5.33mM NaIO4 was used, and one Smith degradation (i.e. treatment in sequence with periodate, borohydride and mild acid) of CEA removed approximately 50% of the carbohydrate, including all of the fucose, sialic acid and 2-acetamido-2-deoxygalactose but did not change the antigenic activity.

Lability of human creatine kinase isoenzymes at 37 degrees C: a complication of electrophoretic separation

The activity of the brain specific isoenzyme of creatine kinase is shown to fall off rapidly at 37 degrees C, particularly in the presence of albumin. Dithiothreitol cannot reverse this lability. The implications of this finding suggest that electrophoretic techniques which use incubation methods to detect the brain specific isoenzyme of creatine kinase may underestimate the true activity.

A gas chromatographic method for measuring 6-mercaptopurine in serum

A method is presented for the measurement of 6-mercaptopurine (6-MP) in serum. Serum samples containing the drug were treated with dithioerythritol and saturated with ammonium carbonate. 6-MP was then extracted from the serum with a mixture of isopropanol-ethyl acetate (1:1, v/v) containing 0.01% ethanethiol. The solvent was evaporated, the residue dissolved in dilute hydrocholoric acid, washed with chloroform, and extracted with ethyl acetate. 6-MP was derivatized with trimethylanilinium hydroxide and measured gas chromatographically. The sulfhydryl-protecting reagents, dithioerythritol and ethanethiol, were added to prevent the decomposition of 6-MP. The extraction and clean-up method recovered 78 +/- 2% (S.E.) of the 6-MP present. Tracer amounts of [8-14C]6-MP served as the internal standard during the extraction part of the method. Theophyline was used as the internal standard during the gas chromatographic analysis. The standard curve obtained from the gas chromatograph was linear between 0.5 and 20 mug/ml of 6-MP. Serum samples were stored in the freezer for two weeks without significant loss of drug. No interference was encountered from normal serum constituents or xanthines, such as caffeine or theophylline added to serum.

Solubilization of human spermatozoa and antigen isolation responsable for agglutination

Spermatozoa were solubilized by cleaving the disulphide bonds with dithioerythrol and protecting the weak antigen responsable for spermagglutination with Na-dodecylsulphate. The fact that spermagglutinating activity could still be absorbed from female sera by solubilized spermatozoa indicates that the antigen has not been destroyed by the applied procedure. By gelelectrophoresis four fractions could be separated. Antibody fraction from four sera and three cervical mucus samples of women with humoral spermagglutinating antibody--activity were used as indicator antbodies in crossed immunoelectrophoresis of solubilized spermatozoa. As negative controls served four sera and two cervical mucus samples. A precipitation line could only be detected in positive cases. The second spermfraction of gel-electrophoresis was found to contain the antigen reacting with the known antibodies from the applied FD-positive sera and cervical mucus samples.

The isolation and characterization of the V-H domain from rabbit heavy chains of different a locus allotype

The Fd fragment of rabbit gamma-chains was split by papain to yield a smaller fragment with a molecular weight of approximately 14,000 and dialyzable small peptides and amino acids. The domain size fragment was identified as intact variable region from its amino acid content, its blocked amino-terminus, and two characteristic cysteine-containing peptides, while the small peptides and amino acids were accounted for by the degradation of the C-H1 region. The variable regions isolated from Aa1 and Aa3 Fd fragments not only reacted quantitatively with immunoadsorbents conjugated with the homologous anti-a allotype antibody, but also completely inhibited the binding of the parent Fd fragment to the homologous antibody as measured by radioimmune assay. These data provide direct evidence that the group a allotypic determinants are contained entirely in the variable portion and are independent of the constant portion of rabbit heavy chains.

Metabolic function and properties of 4-hydroxyphenylacetic acid 1-hydroxylase from Pseudomonas acidovorans

The enzyme 4-hydroxyphenylacetate, NAD(P)H:oxygen oxidoreductase (1-hydroxylating) (EC 1.14.13 ...; 4-hydroxyphenylacetate 1-monooxygenase; referred to here as 4-HPA 1-hydroxylase) was induced in Pseudomonas acidovorans when 4-hydroxyphenylacetate (4-PHA) was utilized as carbon source for growth; homogentisate and maleylacetoacetate were intermediates in the degradation of 4-HPA. A preparation of the hydroxylase that was free from homogentisate dioxygenase and could be stored at 4 C in the presence of dithioerythritol with little loss of activity was obtained by ultracentrifuging cell extracts; but when purified 18-fold by affinity chromatography the enzyme became unstable. Flavin adenine dinucleotide and Mg2+ ions were required for full activity. 4-HPA 1-hydrocylase was inhibited by KCl, which was uncompetitive with 4-HPA. Values of Ki determined for inhibitors competitive with 4-HPA were 17 muM dl-4-hydroxymandelic acid, 43 muM 3,4-dihydroxyphenylacetic acid, 87 muM 4-hydroxy-3-methylphenylacetic acid, and 440 muM 4-hydroxyphenylpropionic acid. Apparent Km values for substrates of 4-HPA 1-hydroxylase were 31 muM 4-HPA, 67 muM oxygen, 95 muM reduced nicotinamide adenine dinucleotide (NADH); AND 250 muM reduced nicotinamide adenine dinucleotide phosphate (NADPH). The same maximum velocity was given by NADH and NADPH. A chemical synthesis is described for 2-deutero-4-hydroxyphenylacetic acid. This compound was enzymatically hydroxylated with retention of half the deuterium in the homogentisic acid formed. Activity as substrate or inhibitor of 4-HPA 1-hydroxylase was shown only by those analogues of 4-HPA that possessed a hydroxyl group substituent at C-4 of the benze nucleus. A mechanism is suggested that accounts for this structural requirement and also for the observation that when 4-hydroxyphenoxyacetic acid was attacked by the enzyme, hydroquinone was formed by release of the side chain, probably as glycolic acid. Only one enantiometer of racemic 4-hydroxyhydratropic acid was attacked by 4-HPA 1-hydroxylase; the product, alpha-methylhomogentisic acid (2-(2,5-dihydroxyphenyl)-propionic acid), exhibited optical activity. This observation suggests that, during its shift from C-1 to C-2 of the nucleus, the side chain of the substrate remains bound to a site on the enzyme while a conformational change of the protein permits the necessary movement of the benzene ring.