Haloalcohol dehalogenases are bacterial enzymes that catalyze the cofactor‐independent dehalogenation of vicinal haloalcohols such as the genotoxic environmental pollutant 1,3‐dichloro‐2‐propanol, ...thereby producing an epoxide, a chloride ion and a proton. Here we present X‐ray structures of the haloalcohol dehalogenase HheC from Agrobacterium radiobacter AD1, and complexes of the enzyme with an epoxide product and chloride ion, and with a bound haloalcohol substrate mimic. These structures support a catalytic mechanism in which Tyr145 of a Ser‐Tyr‐Arg catalytic triad deprotonates the haloalcohol hydroxyl function to generate an intramolecular nucleophile that substitutes the vicinal halogen. Haloalcohol dehalogenases are related to the widespread family of NAD(P)H‐dependent short‐chain dehydrogenases/reductases (SDR family), which use a similar Ser‐Tyr‐Lys/Arg catalytic triad to catalyze reductive or oxidative conversions of various secondary alcohols and ketones. Our results reveal the first structural details of an SDR‐related enzyme that catalyzes a substitutive dehalogenation reaction rather than a redox reaction, in which a halide‐binding site is found at the location of the NAD(P)H binding site. Structure‐based sequence analysis reveals that the various haloalcohol dehalogenases have likely originated from at least two different NAD‐binding SDR precursors.
Legal wrangles continue after a US judge demanded videos showing forced nasogastric feeding in Guantanamo be made public. Force feeding should play no part in the care of mentally competent patients, ...says W John Kalk, who treated hunger striking prisoners in South Africa during the apartheid era
Coronary heart disease (CHD) is rare in diabetic Africans in South Africa, unlike diabetic African-Americans, despite moderate levels of conventional risk factors, with absence of the usual male ...predominance. Because the metabolic syndrome and insulin resistance (IR) are associated with CHD, we have analyzed the prevalence and severity of the metabolic syndrome, and IR, in African and white subjects with type 2 diabetes.
A total of 500 African and 254 white diabetic patients were evaluated for features of the metabolic syndrome (International Diabetes Federation IDF definition); insulin resistance (homeostasis model assessment-insulin resistance HOMA-IR) was calculated in subgroups.
In men, Africans had a lower body mass index (BMI) and smaller waists than white subjects (p < 0.0001); the metabolic syndrome was present in 46.5% and 74.1% of African and white patients respectively (p < 0.0001). In women, frequencies of the metabolic syndrome were similar, but severe metabolic syndrome (4 or 5 criteria) was more frequent in the white group (73.1%) than in the Africans (52.9%) (p = 0.0003). The prevalence of hypertriglyceridemia was lower in African men and women (p < 0.0001) and contributed to their lower prevalence of the metabolic syndrome/severe metabolic syndrome. Compared with the white patients, in African subjects HOMA-IR was 40% lower (p < 0.0001), and correlated with the triglyceride:high-density lipoprotein cholesterol ratio (TG:HDL-C) (r = 0.409, p < 0.0001).
In diabetic Africans, in comparison with white patients, the lower prevalence of the metabolic syndrome in men and severe metabolic syndrome in women, and lesser insulin resistance, might contribute to their lower risk of CHD; the higher prevalence in women might contribute to the reversal of the male:female ratio. The TG:HDL-C ratio appears to be a valid estimate of insulin resistance in diabetic Africans.
The three-dimensional structure of glycosomal glyceraldehyde-3-phosphate dehydrogenase D-glyceraldehyde-3-phosphate: NAD+ oxidoreductase (phosphorylating), EC 1.12.1.12 from the sleeping-sickness ...parasite Trypanosoma brucei was solved by molecular replacement at 3.2-angstrom resolution with an X-ray data set collected by the Laue method. For data collection, three crystals were exposed to the polychromatic synchrotron X-ray beam for a total of 20.5 sec. The structure was solved by using the Bacillus stearothermophilus enzyme model Skarzynski, T., Moody, P. C. E. and Wonacott, A. J. (1987) J. Mol. Biol. 193, 171-187 with a partial data set which was 37% complete. The crystals contain six subunits per asymmetric unit, which allowed us to overcome the absence of 60% of the reflections by 6-fold density averaging. After molecular dynamics refinement, the current molecular model has an R factor of 17.6%. Comparing the structure of the trypanosome enzyme with that of the homologous human muscle enzyme, which was determined at 2.4-angstrom resolution, reveals important structural differences in the NAD binding region. These are of great interest for the design of specific inhibitors of the parasite enzyme
Global climate and the concentration of atmospheric carbon dioxide (CO2) are correlated over recent glacial cycles. The combination of processes responsible for a rise in atmospheric CO2 at the last ...glacial termination (23,000 to 9,000 years ago), however, remains uncertain. Establishing the timing and rate of CO2 changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context. Here we present CO2 and methane (CH4) records of the last deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology. We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO2 occurred in three sudden steps, each of 10 to 15 parts per million. Every step took place in less than two centuries and was followed by no notable change in atmospheric CO2 for about 1,000 to 1,500 years. Slow, millennial-scale ventilation of Southern Ocean CO2-rich, deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO2 associated with the glacial termination, given the strong covariance of CO2 levels and Antarctic temperatures. Our data establish a contribution from an abrupt, centennial-scale mode of CO2 variability that is not directly related to Antarctic temperature. We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.
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Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Haloalkane dehalogenase (DhlA) catalyzes the hydrolysis of haloalkanes via an alkyl−enzyme intermediate. Trp175 forms a halogen/halide-binding site in the active-site cavity together with Trp125. To ...get more insight in the role of Trp175 in DhlA, we mutated residue 175 and explored the kinetics and X-ray structure of the Trp175Tyr enzyme. The mutagenesis study indicated that an aromatic residue at position 175 is important for the catalytic performance of DhlA. Pre-steady-state kinetic analysis of Trp175Tyr-DhlA showed that the observed 6-fold increase of the K m for 1,2-dibromoethane (DBE) results from reduced rates of both DBE binding and cleavage of the carbon−bromine bond. Furthermore, the enzyme isomerization preceding bromide release became 4-fold faster in the mutant enzyme. As a result, the rate of hydrolysis of the alkyl−enzyme intermediate became the main determinant of the k cat for DBE, which was 2-fold higher than the wild-type k cat. The X-ray structure of the mutant enzyme at pH 6 showed that the backbone structure of the enzyme remains intact and that the tyrosine side chain lies in the same plane as Trp175 in the wild-type enzyme. The Clα-stabilizing aromatic rings of Tyr175 and Trp125 are 0.7 Å further apart and due to the smaller size of the mutated residue, the volume of the cavity has increased by one-fifth. X-ray structures of mutant and wild-type enzyme at pH 5 demonstrated that the Tyr175 side chain rotated away upon binding of an acetic acid molecule, leaving one of its oxygen atoms hydrogen bonded to the indole nitrogen of Trp125 only. These structural changes indicate a weakened interaction between residue 175 and the halogen atom or halide ion in the active site and help to explain the kinetic changes induced by the Trp175Tyr mutation.
To assess whether moderate dietary protein restriction can delay the progression of overt diabetic nephropathy, 22 subjects with insulin-dependent diabetes mellitus were randomly assigned to an ...unrestricted protein diet (> 1.6 g.kg body wt-1.d-1) or a moderately protein-restricted diet (0.8 g.kg body wt-1.d-1) and followed prospectively for six mo. Direct isotope methods were used to assess renal function. Protein intake was assessed by measurement of urinary urea nitrogen. The two groups were well-matched for age, sex, duration of diabetes, glycemic control, blood pressure, and degree of renal insufficiency. Patients consuming the unrestricted protein diet (n = 11) showed a progressive decline in glomerular filtration rate of 1.3 mL.min-1.mo-1 with no change in proteinuria. Patients consuming the moderately protein-restricted diet showed a marked decrease in the degree of proteinuria (2.15-1.13 g/d, P = 0.036) and a stabilization of glomerular filtration rate. This occurred independently of changes in blood pressure or glycemic control. Moderate dietary protein restriction can ameliorate progression of overt diabetic nephropathy.
SUMMARY
Aims This study investigated the association between glutamic acid decarb‐ oxylase antibodies (GAD‐AB) and Type 1, Type 2, pancreatic and lipoatrophic diabetes mellitus (DM) in South African ...patients.
Methods Four groups were selected: group A, 100 Black Type 1 DM patients (age at onset < 35 years, body mass index (BMI) < 27 kg/m2 and insulin dependent within 1 year of presentation); group B, 80 Black Type 2 DM patients (age at onset > 35 years, BMI > 27 kg/m2 and controlled on oral hypoglycaemic agents for at least 1 year after presentation); group C, 10 patients of varying ethnicity with DM or impaired glucose tolerance secondary to chronic pancreatitis; group D, five patients of varying ethnicity with DM associated with total lipodystrophy. Fifty healthy Black control subjects were also studied (group E). Serum GAD‐AB and random C‐peptide levels were measured by radioimmunoassay.
Results Mean C‐peptide concentration was significantly lower in Type 1 DM patients than Type 2 DM patients (P < 0.00001). Forty‐four patients with Type 1 DM were GAD‐AB‐positive compared to two patients with Type 2 DM. Two control subjects were also GAD‐AB‐positive. No patient in the other groups had a titre > 1 U/ml. Type 1 DM patients who were GAD‐AB‐positive did not differ from those who were GAD‐AB‐negative for age at onset, duration of DM or C‐peptide concentrations.
Conclusions Auto‐immune beta‐cell destruction has an important role in the pathogenesis of Type 1 DM amongst African patients. However, Type 2 African DM patients and other diabetes subtypes are largely GAD‐AB‐negative.
The effects of regular voluntary (habitual) exercise on left ventricular (LV) diastolic performance, as well as on those hemodynamic, LV geometric and myocardial interstitial changes that influence ...myocardial diastolic function, were examined in streptozocin (50 mg/kg)-induced diabetes mellitus (DM) in male rats. After 16 wk of regular exercise on voluntary running wheels, cardiac performance was measured in anesthetized open-chest ventilated rats. Rats with DM developed a decrease in LV end-diastolic (LVED) chamber and myocardial wall compliance associated with an increase in myocardial collagen fluorescence (a measure of collagen advanced glycosylation end product concentrations), an increase in systemic blood pressure, and a dilated LV. However, LV end-systolic elastance and total myocardial hydroxyproline concentration were unchanged. Habitual exercise prevented the augmented LVED chamber stiffness (slope of linearized LVED pressure-strain relation, DM vs. exercise DM, P < 0.01) and myocardial wall stiffness (slope of linearized LVED stress-strain relation, DM vs. exercise DM, P < 0.001) produced by DM. However, neither markers of blood glucose control, blood pressure, LV geometry, myocardial hydroxyproline concentration, nor collagen fluorescence were altered by the exercise program. A reduced LVED chamber and myocardial wall stiffness, as noted in euglycemic control rats in response to regular exercise, was also not associated with hemodynamic or myocardial interstitial alterations. Therefore, regular voluntary exercise opposes the decrement in myocardial diastolic performance produced by DM in male rats without influencing the accumulation of myocardial advanced glycosylation end products thought to be partly responsible for the stiff myocardium after chronic hyperglycemia. The beneficial effects of regular exercise on myocardial compliance are likely to be a consequence of changes in active as opposed to passive properties of the myocardial wall.
The aim of this review was to identify systematically, criteria for trismus in head and neck cancer, the evidence for risk factors for trismus and the interventions to treat trismus. Three databases ...were searched (time period 1966 to June 2003) for the text “trismus” or “restricted mouth opening”. Included in the review were clinical studies (⩾10 patients). Two observers independently assessed the papers identified. In 12 studies nine different criteria for trismus were found without justifying these criteria. Radiotherapy (follow-up: 6–12 months) involving the structures of the temporomandibular joint and or pterygoid muscles reduces mouth opening with 18% (sd: 17%). Exercises using a therabite device or tongue blades increase mouth opening significantly (no follow-up), effect sizes (ES) 2.6 and 1.5 respectively. Microcurrent electrotherapy (follow-up 3 months) and pentoxifylline (no follow-up) increases mouth opening significantly (ES for both: 0.3).
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