Urease-aided calcium carbonate mineralization for engineering applications: A review.

Inducing calcium carbonate precipitation is another important function of urease in nature. The process takes advantage of the supply of carbonate ions derived from urea hydrolysis and of an increase in pH generated by the reaction, effects that in the presence of Ca ions lead to the precipitation of CaCO. Further to its importance in nature, if performed in a biomimetic manner, the urease-aided CaCO mineralization offers enormous potential in innovative engineering applications as an eco-friendly technique operative under mild conditions, to be used for remediation and cementation/deposition in field applications .

Temperature- and pressure-dependent stopped-flow kinetic studies of jack bean urease. Implications for the catalytic mechanism.

Urease, a Ni-containing metalloenzyme, features an activity that has profound medical and agricultural implications. The mechanism of this activity, however, has not been as yet thoroughly established. Accordingly, to improve its understanding, in this study we analyzed the steady-state kinetic parameters of the enzyme (jack bean), K (M) and k (cat), measured at different temperatures and pressures.

Probing the modes of antibacterial activity of chitosan. Effects of pH and molecular weight on chitosan interactions with membrane lipids in Langmuir films.

Chitosan, a cationic biopolymer derived from chitin, has been described as having antibacterial activity. The modes of this activity, however, have not been established. One mode proposed is that chitosan perturbs bacterial cell membranes.

Urease activity and L-ascorbic acid.

In this work, we studied the behaviours of urease in the presence of l-ascorbic acid (AA) and dehydroascorbic acid (DHA) in different conditions. The inactivations of urease were carried out in an unbuffered and buffered system. We show that in the unbuffered system AA inactivated urease in a biphasic manner by denaturation brought about by AA-lowered pH.

The estimation of oxidative stress markers and apoptosis in right atrium auricles cardiomyocytes of patients undergoing surgical heart revascularisation with the use of warm blood cardioplegia.

Oxidative stress markers and apoptosis were estimated during elective surgical heart revascularization. Eight patients with good ejection fraction underwent coronary artery bypass grafting (CABG) with the use of warm blood cardioplegia. Two right atrium auricle biopsy specimens were collected before and after the operation.

DNA-poly(diallyldimethylammonium chloride) complexation and transfection efficiency.

The present work assesses the influence of the cationic charge density (CD) and the cationic valence of poly(diallyldimethylammonium chloride) (pDADMAC) on the DNA compaction and subsequent transfection. Four homopolymers (CD = 1, with different valences) and one copolymer, poly(acrylamide-co-diallyldimethylammonium chloride) (coDADMAC) (CD < 1, equivalent in valence to one of the homopolymers), were studied. The characterization of the DNA-pDADMAC complexes (polyplexes) as a function of the polycation nitrogen to DNA phosphate molar ratios, N/P, was done by means of conductometry, electrophoretic mobility (zeta-potential), dynamic light scattering (DLS), isothermal titration calorimetry (ITC), atomic force microscopy (AFM), and beta-galactosidase (ONPG) and luciferase expression assays at 25 degrees C and physiological pH.

Mono- (Ag, Hg) and di- (Cu, Hg) valent metal ions effects on the activity of jack bean urease. Probing the modes of metal binding to the enzyme.

The inhibition of urease by heavy metal ions has been habitually ascribed to the reaction of the ions with enzyme thiol groups, resulting in the formation of mercaptides. To probe the modes of metal binding to the enzyme, in this work the reaction of mono- (Ag, Hg) and di- (Cu, Hg) valent metal ions with jack bean urease was studied. The enzyme was reacted with different concentrations of the metal ions for different periods of times, when its residual activity was assayed and thiol content titrated.

Behavior of silica particles introduced into an isolated rat heart as potential drug carriers.

Silica powders consisting of small spherical particles (50-200 nm) have been obtained by the sol-gel method. A suspension of such particles in the Krebs-Hanseleit solution has been introduced into the coronary circulation of a beating perfused rat heart. The influence of the suspension on the heart muscle and the coronary vessels in the rat body has been histopathologically examined.

Chitosan as a lipid binder: a langmuir monolayer study of chitosan-lipid interactions.

Owing to its distinct chemico-biological properties, chitosan, a cationic biopolymer, offers a great potential in multifarious bioapplications. One such application is as a dietary antilipidemic supplement to be used to reduce obesity/overweight and to lower cholesterol. The lipid-binding efficiency of chitosan, however, remains debatable.

Jack bean urease: the effect of active-site binding inhibitors on the reactivity of enzyme thiol groups.

In view of the complexity of the role of the active site flap cysteine in the urease catalysis, in this work we studied how the presence of typical active-site binding inhibitors of urease, phenylphosphorodiamidate (PPD), acetohydroxamic acid (AHA), boric acid and fluoride, affects the reactivity of enzyme thiol groups, the active site flap thiol in particular. For that the inhibitor-urease complexes were prepared with excess inhibitors and had their thiol groups titrated with DTNB. The effects observed were analyzed in terms of the structures of the inhibitor-urease complexes reported in the literature.

Double mode of inhibition-inducing interactions of 1,4-naphthoquinone with urease: arylation versus oxidation of enzyme thiols.

In their inhibition-inducing interactions with enzymes, quinones primarily utilize two mechanisms, arylation and oxidation of enzyme thiol groups. In this work, we investigated the interactions of 1,4-naphthoquinone with urease in an effort to estimate the contribution of the two mechanisms in the enzyme inhibition. Jack bean urease, a homohexamer, contains 15 thiols per enzyme subunit, six accessible under non-denaturing conditions, of which Cys592 proximal to the active site indirectly participates in the enzyme catalysis.

Quinone-induced inhibition of urease: elucidation of its mechanisms by probing thiol groups of the enzyme.

In this work we studied the reaction of four quinones, 1,4-benzoquinone (1,4-BQ), 2,5-dimethyl-1,4-benzoquinone (2,5-DM-1,4-BQ), tetrachloro-1,4-benzoquinone (TC-1,4-BQ) and 1,4-naphthoquinone (1,4-NQ) with jack bean urease in phosphate buffer, pH 7.8. The enzyme was allowed to react with different concentrations of the quinones during different incubation times in aerobic conditions.

Jack bean (Canavalia ensiformis) urease. Probing acid-base groups of the active site by pH variation.

A pH-variation study of jack bean (Canavalia ensiformis) urease steady-state kinetic parameters and of the inhibition constant of boric acid, a urease competitive inhibitor, was performed using both noninhibitory organic (MES, HEPES and CHES) and inhibitory inorganic (phosphate) buffers, in an effort to elucidate the functions exercised in the catalysis by the ionizable groups of the enzyme active site. The results obtained are consistent with the requirement for three groups utilized by urease with pK(a)s equal to 5.3+/-0.

Exercise-induced apoptosis in renal tubular cells of the rat.

A number of studies have shown that acute physical exercise is associated with the induction of apoptosis not only in skeletal muscle but also in many distant organs. One of the pathogenic agents responsible for exercise-induced damage in many tissues is the generation of oxygen free radicals. The aim of the present study was to examine the influence of exercise-induced oxidative stress on the rat kidney.

Heavy metal ions inhibition of jack bean urease: potential for rapid contaminant probing.

The kinetics of heavy metal ions inhibition of jack bean urease was studied by progress curve analysis in a reaction system without enzyme-inhibitor preincubation. The inhibition was found to be biphasic with an initial, small inhibitory phase changing over the time course of 5-10 min into a final linear steady state with a lower velocity. This time-dependent pattern was best described by mechanism B of slow-binding inhibition, involving the rapid formation of an EI complex that subsequently undergoes slow conversion to a more stable EI* complex.

Multi-step analysis of Hg2+ ion inhibition of jack bean urease.

We performed a multi-step analysis of the inhibition of jack bean urease by Hg(2+) ions that included residual activity measurements after incubation of the enzyme with the metal ion, reactivation of Hg(2+)-inhibited urease, protection of urease with thiol reagents prior to incubation with Hg(2+), progress curve analysis, and spectroscopic assay of thiol groups in urease-Hg(2+) complexes with a cysteine selective agent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). Hg(2+) ions were found to form stable complexes with urease that could rapidly be reversed only by the treatment with dithiotreitol, and not by dilution or dialysis. The residual activity data interpreted in terms of the Hill equation revealed the multisite Hg(2+) inhibition of urease, and along with the DTNB thiol-assay they demonstrated the involvement in the reaction with Hg(2+) of six cysteine residues per enzyme subunit, including the active-site flap cysteine.

Histological and electron microscopic investigation of Reinke's edema.

Reinke's edema is a benign lesion of vocal fold affecting subepithelial space. This paper describes the histological features of Reinke's edema on the basis of an extensive number of cases (203 women and 58 men). In 10 cases the electron microscopic examination was performed.

[Renovascular hypertension with high serum zinc in serum of a patient with ceroid-lipofuscinosis and genome 46,XY,9qh+].

A case of a 38-year-old patient with severe renovascular hypertension high serum zinc concentration and ceroidlipofuscinosis was presented. The diagnosis of ceroidlipofuscinosis was based on electron microscope picture of mucosus tissue of rectum where the secondary lisosoms, so characteristic of this disease, were found in cells of connective tissue.

Determination of blood serum oncoprotein NEU and antioncoprotein p-53--molecular biomarkers in various types of occupational exposure.

Application of various diagnostic tests for occupational cancer risk monitoring is associated with the fact that gene mutations and changes in gene expression correspond to the earliest stages of carcinogenesis, namely early stages of the promotion process. The changes in protooncogenes and suppressor genes can be detected either at the genome level, at the level of transferring the genetic information from DNA to protein, or at the level of protein synthesis controlled by genes (oncogenes or antioncogenes). In the latter instance, as the concentrations of these proteins are considerably increased, their quantities in blood serum can be determined by the immunochemical methods.

[Urinary cotinine as a biomarker of exposure to tobacco smoke].

Several markers are used to monitor active or passive exposure to tobacco smoke. They include measurements of carboxyhaemoglobin in the blood, carbon dioxide in the expired air, thiocyanates and nicotine in the saliva, plasma (serum) or urine. The determination of cotinine, the main nicotine metabolite, in biological fluids is a biomarker which finds still wider application.

Determination of tissue polypeptide antigens (TPA) and carcinoembryonic antigen (CEA) in serum: its value in the preliminary cancer risk assessment in asbestos exposed workers.

Seeking the changes at the cellular level or at the level of cellular metabolism products, present in the biological fluids, in order to detect early stages of the carcinogenic process is an essential step in preventing cancer development among asbestos exposed workers. Carcinogenic biomarkers such as tissue polypeptide antigens (TPA) and carcinoembryonic antigen (CEA) were found very useful in this attempt. The objective of this work was to identify individuals at critical cancer risk in the population of workers exposed to asbestos and to evaluate the value of TPA and CEA determinations for this particular purpose.