BACKGROUND: Brooklyn Chest Hospital (BCH) is a specialised TB hospital in Cape Town, South Africa. We describe reasons for admission, patient profiles and hospital-discharge outcomes in children ...admitted to BCH. This was compared to a previous study (2000-2001).METHODS:
This retrospective, descriptive study included all children (0-14 years) admitted to BCH from January 2016 to December 2017. Data collected from patient folders and a laboratory database included demographic data, reasons for admission, clinical data and hospital outcomes.RESULTS:
Of 263 children admitted, 133 (50.6%) were male. The median age was 32 months (IQR 15-75); 48 (18.3%) were HIV-positive and 150 (57.0%) had bacteriologically confirmed TB. Reasons for admission included social/caregiver-related (n = 119, 45.2%), drug-resistant TB (n = 114,
43.3%), TB meningitis (n = 86, 32.7%) and other severe types of TB (n = 63, 24.0%); 110 (41.8%) children had >1 reason for admission. TB meningitis admissions decreased (P = 0.014) and those for drug-resistant TB increased (P < 0.001) compared to 2000-2001.
Pulmonary TB was diagnosed in 234 (89.0%), extrapulmonary TB in 149 (56.7%) and 126 (47.9%) had both. At discharge, 73 (27.8%) had completed treatment, 182 (69.2%) were transferred out to complete treatment at community clinics, and 6 (2.3%) died.CONCLUSIONS: Although most children
were admitted for clinical reasons, social/caregiver-related reasons were also important.
To establish the contribution of eight founder alleles in three DNA damage repair genes (BRCA1, CHEK2 and NBS1) to prostate cancer in Poland, and to measure the impact of these variants on survival ...among patients.
Three thousand seven hundred fifty men with prostate cancer and 3956 cancer-free controls were genotyped for three founder alleles in BRCA1 (5382insC, 4153delA, C61G), four alleles in CHEK2 (1100delC, IVS2+1G>A, del5395, I157T), and one allele in NBS1 (657del5).
The NBS1 mutation was detected in 53 of 3750 unselected cases compared with 23 of 3956 (0.6%) controls (odds ratio (OR)=2.5; P=0.0003). A CHEK2 mutation was seen in 383 (10.2%) unselected cases and in 228 (5.8%) controls (OR=1.9; P<0.0001). Mutation of BRCA1 (three mutations combined) was not associated with the risk of prostate cancer (OR=0.9; P=0.8). In a subgroup analysis, the 4153delA mutation was associated with early-onset (age ≤ 60 years) prostate cancer (OR=20.3, P=0.004). The mean follow-up was 54 months. Mortality was significantly worse for carriers of a NBS1 mutation than for non-carriers (HR=1.85; P=0.008). The 5-year survival for men with an NBS1 mutation was 49%, compared with 72% for mutation-negative cases.
A mutation in NBS1 predisposes to aggressive prostate cancer. These data are relevant to the prospect of adapting personalised medicine to prostate cancer prevention and treatment.
Nutrient limitation is a critical signal in Salmonella virulence gene regulation. The katF (rpoS) gene mediates the expression of the Salmonella spv plasmid virulence genes during bacterial ...starvation. A katF Salmonella mutant has increased susceptibility to nutrient deprivation, oxidative stress, acid stress, and DNA damage, conditions which are relevant to the intraphagosomal environment of host macrophages. Moreover, the katF mutant has significantly reduced virulence in mice. katF encodes an alternative σ factor of RNA polymerase which coordinately regulates Salmonella virulence.
Diversity of properties among catalases Switala, Jacek; Loewen, Peter C
Archives of biochemistry and biophysics,
05/2002, Volume:
401, Issue:
2
Journal Article
Peer reviewed
Catalases from 16 different organisms including representatives from all three phylogenetic clades were purified and characterized to provide a comparative picture of their respective properties. ...Collectively the enzymes presented a diverse range of activities and properties. Specific activities ranged from 20,700 to 273,800 units per milligram of protein and maximal turnover rates ranged from 54,000 to 833,000 per second. The effective concentrations of common catalase inhibitors, cyanide, azide, hydroxylamine, aminotriazole, and mercaptoethanol, varied over a 100- to 1000-fold concentration range, and a broad range of sensitivities to heat inactivation was observed. Michaelis–Menten kinetics were approximately followed only at the low substrate concentrations. At high H
2O
2 concentrations, inactivation of small-subunit enzymes resulted in lower velocities than what were predicted, whereas large-subunit enzymes had velocities higher than predicted. Kinetic constants such as
K
m and
V
max for catalases must be labeled as “apparent.”
Pathogenic microorganisms possess antioxidant defense mechanisms for protection from reactive oxygen metabolites such as hydrogen peroxide (H2O2), which are generated during the respiratory burst of ...phagocytic cells. These defense mechanisms include enzymes such as catalase, which detoxify reactive oxygen species, and DNA repair systems which repair damage resulting from oxidative stress. To determine the relative importance of these two potentially protective defense mechanisms against oxidative stress encountered by Salmonella during infection of the host, a Salmonella typhimurium double mutant unable to produce either the HPI or HPII catalase was constructed, and compared with an isogenic recA mutant deficient in DNA repair. The recA mutant was hypersusceptible to H2O2 at low cell densities in vitro, while the catalase mutant was more susceptible to high H2O2 concentrations at high cell densities. The catalase mutant was found to be resistant to macrophages and retained full murine virulence, in contrast to the recA mutant which previously was shown to be macrophage-sensitive and attenuated in mice. These observations suggest that Salmonella is subjected to low concentrations of H2O2 while at relatively low cell density during infection, conditions requiring an intact DNA repair system but not functional catalase activity.
Catalase-peroxidases are bifunctional peroxidases exhibiting an overwhelming catalase activity and a substantial peroxidase activity. Here we present a kinetic study of the formation and reduction of ...the key intermediate compound I by probing the role of the conserved tryptophan at the distal haem cavity site. Two wild-type proteins and three mutants of Synechocystis catalase-peroxidase (W122A and W122F) and Escherichia coli catalase-peroxidase (W105F) have been investigated by steady-state and stopped-flow spectroscopy. W122F and W122A completely lost their catalase activity whereas in W105F the catalase activity was reduced by a factor of about 5000. However, the mutations did not influence both formation of compound I and its reduction by peroxidase substrates. It was demonstrated unequivocally that the rate of compound I reduction by pyrogallol or o-dianisidine sometimes even exceeded that of the wild-type enzyme. This study demonstrates that the indole ring of distal Trp in catalase-peroxidases is essential for the two-electron reduction of compound I by hydrogen peroxide but not for compound I formation or for peroxidase reactivity (i.e. the one-electron reduction of compound I).
The catalase-peroxidase encoded by
katG of
Burkholderia pseudomallei (BpKatG) is 65% identical with KatG of
Mycobacterium tuberculosis, the enzyme responsible for the activation of isoniazid as an ...antibiotic. The structure of a complex of BpKatG with an unidentified ligand, has been solved and refined at 1.7
Å resolution using X-ray synchrotron data collected from crystals flash-cooled with liquid nitrogen. The crystallographic agreement factors
R and
R
free are 15.3% and 18.6%, respectively. The crystallized enzyme is a dimer with one modified heme group and one metal ion, likely sodium, per subunit. The modification on the heme group involves the covalent addition of two or three atoms, likely a perhydroxy group, to the secondary carbon atom of the vinyl group on ring I. The added group can form hydrogen bonds with two water molecules that are also in contact with the active-site residues Trp111 and His112, suggesting that the modification may have a catalytic role. The heme modification is in close proximity to an unusual covalent adduct among the side-chains of Trp111, Tyr238 and Met264. In addition, Trp111 appears to be oxidized on C
δ1 of the indole ring. The main channel, providing access of substrate hydrogen peroxide to the heme, contains a region of unassigned electron density consistent with the binding of a pyridine nucleotide-like molecule. An interior cavity, containing the sodium ion and an additional region of unassigned density, is evident adjacent to the adduct and is accessible to the outside through a second funnel-shaped channel. A large cleft in the side of the subunit is evident and may be a potential substrate-binding site with a clear pathway for electron transfer to the active-site heme group through the adduct.
A bond between the Nδ of the imidazole ring of His 392 and the Cβ of the essential Tyr 415 has been found in the refined crystal structure at 1.9 Å resolution of catalase HPII of Escherichia coli. ...This novel type of covalent linkage is clearly defined in the electron density map of HPII and is confirmed by matrix‐assisted laser desorption/ionization mass spectrometry analysis of tryptic digest mixtures. The geometry of the bond is compatible with both the sp3 hybridization of the Cβ atom and the planarity of the imidazole ring. Two mutated variants of HPII active site residues, H128N and N201H, do not contain the His 392‐Tyr 415 bond, and their crystal structures show that the imidazole ring of His 392 was rotated, in both cases, by 80° relative to its position in HPII. These mutant forms of HPII are catalytically inactive and do not convert heme b to heme d, suggesting a relationship between the self‐catalyzed heme conversion reaction and the formation of the His‐Tyr linkage. A model coupling the two processes and involving the reaction of one molecule of H2O2 on the proximal side of the heme with compound I is proposed.
1. NADPH binds to bovine catalase and to yeast catalases A and T, but not to Escherichia coli catalase HPII. The association was demonstrated using chromatography and fluorimetry. Bound NADPH ...fluoresces in a similar way to NADPH in solution. 2. Bound NADPH protects bovine and yeast catalases against forming inactive peroxide compound II either via endogenous reductant action or by ferrocyanide reduction during catalytic activity in the presence of slowly generated peroxide. 3. Bound NADPH reduces neither compound I nor compound II of catalase. It apparently reacts with an intermediate formed during the decay of compound I to compound II; this postulated intermediate is an immediate precursor of stable compound II either when the latter is formed by endogenous reductants or when ferrocyanide is used. It represents therefore a new type of hydrogen donor that is not included in the original classification of Keilin and Nicholls Keilin, D. and Nicholls, P. (1958) Biochim. Biophys. Acta 29, 302-307 4. A model for NADPH action is presented in which concerted reduction of the ferryl iron and of a neighbouring protein free radical is responsible for the observed NADPH effects. The roles of migrant radical species in mammalian and yeast catalases are compared with similar events in metmyoglobin and cytochrome c peroxidase reactions with peroxides.
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