The possible role of hydrogen sulfide as a modulator of hemostatic parameters of plasma.

Hydrogen sulfide (H2S) is a well known toxic gas at high levels. However, at physiological levels, H2S may play a role in the pathogenesis of various cardiovascular diseases. The objective was to study the effects of exogenous H2S on the hemostatic parameters (coagulation and fibrinolytic activity) of human plasma. Human plasma was incubated (5, 15 and 30 min) with NaHS as a H2S donor at the final concentration of 0.01-100 µM. Hemostatic factors, such as maximum velocity of clot formation, fibrin lysis half-time, the activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT) were estimated. Moreover, the aim of our study was to establish the influence of NaHS (10 µM; 5, 15 and 30 min) on the clot formation using the purified fibrinogen. We demonstrated that coagulation/fibrinolytic properties of human plasma incubated with NaHS were changed. APPT, PT and TT of plasma treated with NaHS at tested concentrations--0.01-100 µM were prolonged. We observed that NaHS (0.01-100 µM) reduced fibrin polymerization in whole plasma and 10 µM NaHS also reduced polymerization of purified fibrinogen. In the presence of NaHS (at the low tested concentration--1 µM) the decrease was about 18% (in plasma, p<0.05). Our experiments also showed that NaHS (0.01-100 µM) stimulated the fibrin lysis in whole plasma. However, the time-dependent (5, 15 and 30 min) reduction of fibrin/fibrinogen polymerization and stimulation of fibrin lysis by NaHS (10 µM) was not observed. In conclusion, the present study demonstrates the anticoagulant properties of exogenous H2S in vitro.

Structural basis for UTP specificity of RNA editing TUTases from Trypanosoma brucei.

Trypanosomatids are pathogenic protozoa that undergo a unique form of post-transcriptional RNA editing that inserts or deletes uridine nucleotides in many mitochondrial pre-mRNAs. Editing is catalyzed by a large multiprotein complex, the editosome. A key editosome enzyme, RNA editing terminal uridylyl transferase 2 (TUTase 2; RET2) catalyzes the uridylate addition reaction. Here, we report the 1.8 A crystal structure of the Trypanosoma brucei RET2 apoenzyme and its complexes with uridine nucleotides. This structure reveals that the specificity of the TUTase for UTP is determined by a crucial water molecule that is exquisitely positioned by the conserved carboxylates D421 and E424 to sense a hydrogen atom on the N3 position of the uridine base. The three-domain structure also unveils a unique domain arrangement not seen before in the nucleotidyltansferase superfamily, with a large domain insertion between the catalytic aspartates. This insertion is present in all trypanosomatid TUTases. We also show that TbRET2 is essential for survival of the bloodstream form of the parasite and therefore is a potential target for drug therapy.

[Aspartate aminotransferase (glutamic oxalacetic transaminase) and alanine aminotransferase (glutamic pyruvic transaminase)].

With regard to adding Pyridoxal Phosphate (PALP), which combines with the active sites of AST and ALT, JSCC recommends measuring holoenzymes without adding PALP, reflecting the biological reaction. On the other hand, IFCC recommends the measurement of both holoenzymes and apoenzymes when PALP is added, reflecting the total diverted from the internal organs. It is important which recommendation to follow from a clinical point of view and from the viewpoint of reducing gaps in clinical facilities. Further, it is necessary to consider each isozyme as well as the time difference between apoenzyme and holoenzyme diversion from blood to accurately grasp the pathology and understand the measurement.

Denaturation of human Cu/Zn superoxide dismutase by guanidine hydrochloride: a dynamic fluorescence study.

The unfolding of holo and apo forms of human Cu/Zn superoxide dismutase by guanidine hydrochloride has been investigated by steady-state and dynamic fluorescence. In agreement with previous observations, a stabilizing effect of the metal ions on the protein tertiary structure was apparent from comparison of apo- and holoproteins, which both showed a sharp sigmoidal transition though at different denaturant concentrations. The transition was also followed by circular dichroism to check the extent of secondary structure present at each denaturant concentration. The results are incompatible with a simple two-state mechanism for denaturation. The occurrence of a more complicated process is supported by the emission decay properties of the single tryptophanyl residue at different denaturant concentrations. A complex decay function, namely, two discrete exponentials or a continuous distribution of lifetimes, was always required to fit the data. In particular, the width of the lifetime distribution, which is maximum at the transition midpoint, reflects heterogeneity of the tryptophan microenvironment and thus the presence of different species along the denaturation pathway. In the unfolded state, the width of the lifetime distribution is broader than in the folded state probably because the tryptophan residue is affected by a larger number of local conformations. The dissociation of the dimer was also studied by varying the protein concentration at different denaturant concentrations. This process affects primarly the surface of the protein rather than its secondary structure as shown by a comparison between the tryptophan emission decay and circular dichroism data under the same conditions. Another consequence of dissociation is a greater instability in the structure of the monomers, which are more easily unfolded.(ABSTRACT TRUNCATED AT 250 WORDS)

In thiamine deficiency, activation of erythrocyte transketolase by thiamine in vivo exceeds activation by cofactor in vitro.

In 60 thiamine deficient patients, the mean erythrocyte transketolase activity after activation by thiamine diphosphate cofactor in vitro, representing the apparent sum of holoenzyme and apoenzyme activities, was 0.609 (SD 0.166) U/g Hb before thiamine therapy and rose to 0.772 (SD 0.152) U/g Hb immediately after the administration of thiamine to the patients. The difference between these values, 0.163 (SD 0.130) U/g, is the mean activity of transketolase protein which can be activated by thiamine in vivo but not by thiamine diphosphate in vitro. This difference correlated with low initial erythrocyte transketolase activity in these patients, but not with their alcohol intake, liver function or diagnoses.

Leukotriene A4 hydrolase: a zinc metalloenzyme.

Purified human leukotriene A4 hydrolase is shown to contain 1 mol of zinc per mol of enzyme, as determined by atomic absorption spectrometry. The enzyme is inhibited dose-dependently by the chelating agents 8-hydroxy-quinoline-5-sulfonic acid, and 1,10-phenanthroline with KI values of about 2 and 8 x 10(-4) M, respectively, whereas dipicolinic acid and EDTA are ineffective in this respect. The inhibition by 1,10-phenanthroline is time-dependent, and at a concentration of 5 mM, 50% inhibition of enzyme (3 x 10(-7) M) occurs after about 15 min. The zinc atom of leukotriene A4 hydrolase can be removed by dialysis against 1,10-phenanthroline which results in loss of enzyme activity. The catalytic activity is almost completely restored by the addition of stoichiometric amounts of Zn2+ or Co2+.

Clinical chemical methods for the routine assessment of the vitamin status in human populations. Part III: The apoenzyme stimulation tests for vitamin B1, B2 and B6 adapted to the Cobas-Bio analyzer.

The programming of the Cobas-Bio centrifugal analyzer for kinetic tests of transketolase, glutathione reductase and aspartate amino-transferase is described. The results obtained in a population of 200 healthy people of both sexes are reported.

Studies on the active site of pig plasma amine oxidase.

Amine oxidase from pig plasma (PPAO) has two bound Cu2+ ions and at least one pyrroloquinoline quinone (PQQ) moiety as cofactors. It is shown that recovery of activity by copper-depleted PPAO is linear with respect to added Cu2+ ions. Recovery of e.s.r. and optical spectral characteristics of active-site copper parallel the recovery of catalytic activity. These results are consistent with both Cu2+ ions contributing to catalysis. Further e.s.r. studies indicate that the two copper sites in PPAO, unlike those in amine oxidases from other sources, are chemically distinct. These comparative studies establish that non-identity of the Cu2+ ions in PPAO is not a requirement for amine oxidase activity. It is shown through the use of a new assay procedure that there are two molecules of PQQ bound per molecule of protein in PPAO; only the more reactive of these PQQ moieties is required for activity.

UV spectroscopic studies of human erythrocyte superoxide dismutase.

Using UV absorption spectroscopy, first derivative spectroscopy, and UV difference spectroscopy, the active site of human superoxide dismutase is probed. First derivative spectra (dA/d lambda versus lambda) show the HESOD spectrum to be a composite of Phe and Trp absorbance. The 278 and 288 nm Trp absorbance peaks are sensitive to solvent polarity. A 5-10% decrease in these peaks accompanies copper removal from the active site indicating greater solvent access to Trp in the apoenzyme than the holoenzyme. A Trp UV difference peak at 305-310 nm documents the presence or absence of copper at the active site, and documents also the movement of a nonbridging copper-binding His (His 46 or 120) when HESOD is inhibited by azide or when the copper moiety is reduced. Trp absorbances indicate that neither cyanide nor KCl inhibition affects the Cu(II)-His bonds. Phe UV absorbance is increased by the presence of copper at the active site and increased further by the addition of cyanide or azide. Neither Trp nor Phe responds to the presence of zinc in the active site. A molecular graphics program, FRODO, shows Trp and the four Phe residues lying in an approximate ring around the active site of HESOD and thus excellently placed to report on active site perturbations.

Vitamin B6 status in cirrhotic patients in relation to apoenzyme of serum alanine aminotransferase.

Plasma levels of pyridoxal-5'-phosphate (PLP) in cirrhotic patients were significantly lower than in control subjects. However, the plasma total pyridoxal level and urinary 4-pyridoxic acid excretion were not decreased in non-alcoholic patients but in alcoholic patients. In the latter, the percentage of apo alanine aminotransferase was not related to the plasma PLP level, but was significantly correlated with plasma total pyridoxal level and urinary 4-pyridoxic acid excretion. We conclude that alcoholic cirrhotic patients have vitamin B6 deficiency, which is at least responsible for low serum alanine aminotransferase activity.

Apoenzyme of aspartate aminotransferase isoenzymes in maternal plasma during labor and following delivery.

In eight normal mothers the effects of pyridoxal 5'-phosphate (PLP) addition on the plasma activities of aspartate aminotransferase isoenzymes (AST-s and AST-m) during labor and following delivery were investigated. The AST-s activities with and without reactivation by PLP appeared to increase immediately after delivery and they were even higher on the 4th day postpartum. On the other hand, there were significant elevations in both the AST-m activities immediately and at 2 h after delivery, but not on the 4th day postpartum. Of AST isoenzymes measured in the nonstress test, only the relative activation rate of AST-m by PLP added was significantly higher than the control value. The present study may come to the following conclusions: 1) The relative activation rate of plasma AST-m activity by PLP may be a reliable index of vitamin B6 nutritional status during pregnancy. 2) The increases in AST-m activity with and without PLP added during labor suggest a minimal damage of mitochondria in skeletal, cardiac and uterine muscle cells. 3) The AST-s isoenzyme determinations with and without PLP may be especially useful as sensitive indication of erythrocyte and/or liver damage after delivery.

Reactions of bovine serum amine oxidase with NN-diethyldithiocarbamate. Selective removal of one copper ion.

NN-Diethyldithiocarbamate (DDC) was able to bind, at 1.0 mM concentration, only about 50% the Cu(II) ions of bovine plasma amine oxidase. Under reducing conditions, this Cu(II) was removed with inactivation of the enzyme. Up to 90% activity could be recovered by treatment with excess Cu(II). The organic cofactor, sensitive to carbonyl reagents, was reduced in the half-Cu-depleted protein and no longer bound phenylhydrazine. The fully reacted protein, in the presence of 10 mM-DDC, lost 50% Cu(II) upon storage at -20 degrees C, but in this case the residual Cu(II) was in the DDC-bound form and the cofactor was in the oxidized state, as it could still bind phenylhydrazine. In the presence of DDC, the rate of reaction with phenylhydrazine was always low, even at 50% DDC saturation, and all derivatives showed identical modifications of the optical and e.p.r. spectra with respect to the phenylhydrazone of the native protein. It is concluded that the two Cu(II) ions are not equivalent, that removal of a single Cu(II) is sufficient to inhibit the re-oxidation of the organic cofactor, and that both Cu(II) ions are in some way involved in the reaction with phenylhydrazine. After reaction with DDC, the optical and e.p.r. spectra of 63Cu(II)-amine oxidase and of 63Cu(II)-carbonic anhydrase [Morpurgo, Desideri, Rigo, Viglino & Rotilio (1983) Biochim. Biophys. Acta 746, 168-175] are very similar and show distorted equatorial co-ordination to Cu(II) of two sulphur atoms and two magnetically equivalent nitrogen atoms.

Apoenzyme content of serum aminotransferases in patients with a renal allograft treated with cyclosporine A and azathioprine.

In 16 patients with a renal allograft the activity concentrations of aspartate aminotransferase and alanine aminotransferase and the percentage stimulation of both enzymes were investigated. After the transplantation the patients received prednisone and cyclosporine A as immunosuppressive therapy, while exactly 3 months after the date of transplantation prednisone and azathioprine were given as immunosuppressives. In the first period, the percentage increase of the activity concentration of aspartate aminotransferase and alanine aminotransferase upon supplementation of pyridoxal-5'-phosphate in vitro were similar to that of healthy individuals. In the second period, however, the percentage increase of the activity concentration of alanine aminotransferase was much higher than that of aspartate aminotransferase. Cyclosporine A given during a period of about 400 days did not influence the percentage increase of both enzymes. It is concluded that the high stimulation of alanine aminotransferase in the second period depends on the presence of azathioprine or its metabolites in serum.

Plasma pyridoxal 5'-phosphate concentrations in relation to apo-aminotransferase levels in normal, uraemic, and post-myocardial infarct sera.

The concentrations of pyridoxal 5'-phosphate, and the holoenzyme activities and apoenzyme contents of alanine aminotransferase and aspartate aminotransferase in plasma were determined simultaneously in healthy individuals, patients with renal insufficiency with and without chronic haemodialysis and in patients with acute myocardial infarction. Plasma pyridoxal 5'-phosphate is significantly diminished in uraemic patients and in post-myocardial infarct sera, healthy females have lower pyridoxal 5'-phosphate levels (26.2 +/- 9.0 nmol/l) than healthy males (41.0 +/- 15.1 nmol/l). The stimulation in vitro of the activities of aspartate aminotransferase and alanine aminotransferase by addition of pyridoxal 5'-phosphate (0.1 mmol/l) was found to be independent of the endogenous coenzyme level. In sera of uraemic patients without chronic haemodialysis an inverse statistic correlation between pyridoxal 5'-phosphate-induced stimulation of aspartate aminotransferase activity and the concentrations of urea (r = -0.696) and creatinine (r = -0.715) was found. The respective correlations are much weaker for alanine aminotransferase. The apoenzyme fraction was highest in post-myocardial infarct sera. Follow up of these patients did not reveal any relationship between the fluctuations of pyridoxal 5'-phosphate levels and apoenzyme contents of both alanine aminotransferase and aspartate aminotransferase. The results permit the conclusion that the degree of in vitro stimulation of aminotransferases by pyridoxal 5'-phosphate can not be predicted from the endogenous coenzyme level.

Investigation of the effect of metal ions on the reactivity of thiol groups in human 5-aminolaevulinate dehydratase.

The reaction of human 5-aminolaevulinate dehydratase with 5,5'-dithiobis-(2-nitrobenzoic acid) (Nbs2) results in the release of 4 molar equivalents of 5-mercapto-2-nitrobenzoic acid (Nbs) per subunit. Two of the thiol groups reacted very rapidly (groups I and II), and their rate constants were determined by stopped-flow spectrophotometry; the other two thiol groups (groups III and IV) were observed by conventional spectroscopy. Titration of the enzyme with a 1 molar equivalent concentration of Nbs2 resulted in the release of 2 molar equivalents of Nbs and the concomitant formation of an intramolecular disulphide bond between groups I and II. Removal of zinc from the holoenzyme increased the reactivity of groups I and II without significantly affecting the rate of reaction of the other groups. The reactions of the thiol groups in both the holoenzyme and apoenzyme were little affected by the presence of Pb2+ ions at concentrations that strongly inhibit the enzyme, suggesting that Zn2+ and Pb2+ ions may have independent binding sites. Protein fluorescence studies with Pb2+ and Zn2+ have shown that the binding of both metal ions results in perturbation of the protein fluorescence.

Relationship between plasma pyridoxal-5'-phosphate concentration and the apoenzyme content of serum aminotransferases in patients with a renal allograft.

In 76 patients with a renal allograft the plasma concentration of pyridoxal-5'-phosphate, the activity concentrations of aspartate aminotransferase and alanine aminotransferase and the percentage stimulation of both enzymes have been investigated. Generally, the concentration of the coenzyme was decreased in the patient group compared to normal individuals. The percentage increase of aspartate aminotransferase is the same for the patients as for the normal group. However, the stimulation of alanine aminotransferase is greatly increased for the patient group except for those patients who received cyclosporine A instead of azathioprine. The highly significant inverse correlation between the plasma pyridoxal-5'-phosphate concentration and the percentage stimulation of the enzymatic activity of aspartate aminotransferase and alanine aminotransferase observed before for a normal group, is not present in our patient group. The percentage increase is independent on the activity concentration of the enzymes. It is concluded that the high stimulation of alanine aminotransferase depends on the administration of azathioprine.

Selective binding behavior of zinc(II) and copper(II) ions to their native sites of apo-bovine superoxide dismutase.

The four binding constants of zinc(II) ions to apo-bovine superoxide dismutase were measured by the method of equilibrium dialysis. The binding constants (10(11.1)-10(10.9) M-1) of zinc ions to the native zinc sites were much larger than those to the native copper sites (10(7.8)-10(6.5) M-1) at pH 6.25. The competitive reaction between copper(II) and zinc(II) ions for the native copper sites of copper free bovine superoxide dismutase was also investigated. The native copper sites of bovine superoxide dismutase selectively react with copper ions, because the binding constants of copper ions for the native copper sites were much larger (10(6) times) than those of zinc ions.