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Class C (class + c)

Distribution by Scientific Domains
Chemistry63%
Medical Sciences36%

Selected Abstracts

Re-examining the role of Lys67 in class C ,-lactamase catalysis

PROTEIN SCIENCE, Issue 3 2009
Yu Chen
Abstract Lys67 is essential for the hydrolysis reaction mediated by class C ,-lactamases. Its exact catalytic role lies at the center of several different proposed reaction mechanisms, particularly for the deacylation step, and has been intensely debated. Whereas a conjugate base hypothesis postulates that a neutral Lys67 and Tyr150 act together to deprotonate the deacylating water, previous experiments on the K67R mutants of class C ,-lactamases suggested that the role of Lys67 in deacylation is mainly electrostatic, with only a 2- to 3-fold decrease in the rate of the mutant vs the wild type enzyme. Using the Class C ,-lactamase AmpC, we have reinvestigated the activity of this K67R mutant enzyme, using biochemical and structural studies. Both the rates of acylation and deacylation were affected in the AmpC K67R mutant, with a 61-fold decrease in kcat, the deacylation rate. We have determined the structure of the K67R mutant by X-ray crystallography both in apo and transition state-analog complexed forms, and observed only minimal conformational changes in the catalytic residues relative to the wild type. These results suggest that the arginine side chain is unable to play the same catalytic role as Lys67 in either the acylation or deacylation reactions catalyzed by AmpC. Therefore, the activity of this mutant can not be used to discredit the conjugate base hypothesis as previously concluded, although the reaction catalyzed by the K67R mutant itself likely proceeds by an alternative mechanism. Indeed, a manifold of mechanisms may contribute to hydrolysis in class C ,-lactamases, depending on the enzyme (wt or mutant) and the substrate, explaining why different mutants and substrates seem to support different pathways. For the WT enzyme itself, the conjugate base mechanism may be well favored. [source]

Small Vestibular Schwannomas With No Hearing: Comparison of Functional Outcomes in Stereotactic Radiosurgery and Microsurgery

THE LARYNGOSCOPE, Issue 11 2008
Daniel H. Coelho MD
Abstract Objectives: To date, numerous studies have compared functional outcomes between stereotactic radiosurgery (SRS) and microsurgery (MS) in the treatment of vestibular schwannomas (VS). However, most of them involve tumors of difference sizes, radiation dosages, and surgical approaches. Few have systematically compared issues of dysequilibrium. By studying only patients with small tumors and no hearing, we sought to minimize confounding variables. Study Design: A retrospective chart review and telephone questionnaire. Methods: From 1998,2006, 31 patients with small (<1.5 cm) VS and nonserviceable hearing (American Academy of Otolaryngology,Head and Neck Surgery [AAO-HNS] Class C or D) were treated at our institution. Twenty-two were available for follow-up and telephone questionnaire, including the University of California Los Angeles Dizziness Questionnaire (UCLA-DQ). Twelve underwent SRS and 10 underwent MS. All MS patients underwent the translabyrinthine approach to their tumors. Outcomes measurements included tumor control, facial nerve function, tinnitus, trigeminal function, and imbalance. Results: Patients undergoing SRS had comparable rates of tumor control, facial nerve function, tinnitus, and trigeminal function to MS patients. However, SRS did result in statistically significantly worse long-term imbalance when compared with MS patients. Detailed comparisons of the two modalities are made. Conclusions: In our study population, patients with small tumors and no serviceable hearing, these data suggest that MS results in comparable minimal morbidity with SRS, though posttreatment dysequilibrium is significantly decreased. While the authors recommend translabyrinthine resection of small VS with no hearing in patients able to tolerate surgery, the need for further prospective investigation is clear. [source]

Functional significance of hepatic arterial flow reserve in patients with cirrhosis

HEPATOLOGY, Issue 2 2003
Alexander Zipprich
In cirrhosis, hepatic arterial vasodilatation occurs in response to reduced portal venous blood flow. However, although the hepatic arterial flow reserve is high in patients with cirrhosis, its impact on hepatic function is unknown. This study investigated the effect of adenosine-induced hepatic arterial vasodilatation on different markers of liver function. In 20 patients with cirrhosis (Child-Pugh class A/B/C: n = 2/7/11) adenosine (2-30 ,g · min,1 · kg body wt,1) was infused into the hepatic artery and hepatic arterial average peak flow velocities (APV), pulsatility indices (PI), and blood flow volumes (HABF) were measured using digital angiography and intravascular Doppler sonography. Indocyanine green (ICG), lidocaine, and galactose were administered intravenously in doses of 0.5, 1.0, and 500 mg/kg body weight in the presence of adenosine-induced hepatic arterial vasodilatation and, on a separate study day, without adenosine. ICG disappearance, galactose elimination capacity (GEC), and formation of the lidocaine metabolite monoethylglycinxylidide (MEGX) were assessed. Adenosine markedly increased APV and HABF and markedly decreased PI. Serum MEGX concentrations were 63.7 ± 18.2 (median, 62; range, 36-107) and 99.0 ± 46.3 (82.5; 49-198) ng/mL in the absence and presence of adenosine infusion, respectively (P = .001). Adenosine-induced changes in MEGX concentrations were correlated inversely to changes in APV (r = ,0.5, P = .02) and PI (r = ,0.55, P = .01) and were more marked in Child-Pugh class C compared with Child-Pugh class A patients (57.4 ± 49.9 [44; ,14 to 140] vs. 8.4 ± 16.5 [13; ,11 to 35] ng/mL, P < .01). In conclusion, hepatic arterial vasodilatation provides substantial functional benefit in patients with cirrhosis. The effect does not depend directly on hepatic arterial macroperfusion and is observed preferentially in patients with decompensated disease. [source]

Hepatic arterial buffer response in patients with advanced cirrhosis

HEPATOLOGY, Issue 3 2002
Veit Gülberg
Hepatic arterial buffer response (HABR) is considered an important compensatory mechanism to maintain perfusion of the liver by hepatic arterial vasodilation on reduction of portal venous perfusion. HABR has been suggested to be impaired in patients with advanced cirrhosis. In patients with hepatopetal portal flow, placement of a transjugular intrahepatic portosystemic shunt (TIPS) reduces portal venous liver perfusion. Accordingly, patients with severe cirrhosis should have impaired HABR after TIPS implantation. Therefore, the aim of this study was to investigate the effect of TIPS on HABR as reflected by changes in resistance index (RI) of the hepatic artery. A total of 366 patients with cirrhosis (Child-Pugh class A, 106; class B, 168; class C, 92) underwent duplex Doppler ultrasonographic examination with determination of RI and maximal flow velocity in the portal vein before and 1 month after TIPS placement. Portosystemic pressure gradient was determined before and after TIPS placement. In 29 patients with hepatofugal portal blood flow, RI was significantly lower than in 337 patients with hepatopetal flow (0.63 ± 0.02 vs. 0.69 ± 0.01; P < .001). TIPS induced a significant decrease of the RI in patients with hepatopetal flow (RI, 0.69 ± 0.01 before vs. 0.64 ± 0.01 after TIPS; P = .001) but not in patients with hepatofugal flow (RI, 0.63 ± 0.02 before vs. 0.63 ± 0.02 after TIPS; NS). This response was not dependent on the Child-Pugh class. In conclusion, our results suggest that some degree of HABR is preserved even in patients with advanced cirrhosis with significant portal hypertension. [source]

Long-term follow-up of nevirapine-treated patients in a single-centre cohort

HIV MEDICINE, Issue 8 2009
M Colafigli
Objectives We reviewed the safety and efficacy of nevirapine (NVP)-based therapy in all patients initiating NVP-containing combined antiretroviral therapy [cART (,3 drugs)] in our clinic since 1994. Methods Patient characteristics and laboratory values from the start of the NVP-based cART regimen to the last available follow-up or to NVP discontinuation were retrieved from an observational database. Results Five hundred and seventy-three patients were treated with NVP-based cART for a median of 18.4 (range 0.1,128.8) months. The 1-year cumulative estimated probability of discontinuing NVP-containing regimens for toxicity was 0.203. Only 1.9% developed a grade 3 alanine aminotransferase (ALT) elevation. Significant increases in high-density lipoprotein cholesterol were observed up to month 12 except in treatment-naïve patients, where the increase was limited to 3 months. Discontinuation because of cutaneous reaction was predicted independently by female gender [Hazard Ratio (HR) 3.21, P<0.001] and Centers for Disease Control class C (HR 0.50, P=0.012). Discontinuation because of liver toxicity was predicted independently by anti-hepatitis C virus positivity (HR 3.84, P<0.001). In patients starting NVP-containing cART with undetectable viral loads, the 5-year estimated probability of viral load >400 HIV-1 RNA copies/mL was 0.34. Conclusions Long-term follow-up with an NVP-containing cART showed a low rate of discontinuation caused by liver toxicity and the maintenance of virological suppression in patients switched with undetectable viral loads. [source]

Evaluation of hernia repair operation in Child,Turcotte,Pugh class C cirrhosis and refractory ascites

JOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 3 2007
Joo Kyung Park
Abstract Background and Aim:, Abdominal wall hernia is a common feature of decompensated liver cirrhosis and frequently causes life-threatening complications or severe pain. However, there have been no data reported on postoperative mortality, hepatic functional deterioration and recurrence rate according to Child,Turcotte,Pugh (CTP) class and to the presence of refractory ascites. Methods:, The study population comprised 53 liver cirrhosis patients who underwent hernia repair operation. Comparisons were made of 30-day mortality among the different CTP classes, and between those with or without refractory ascites. Liver function was also analyzed just before the operation, in the immediate postoperative period, and in the remote postoperative period. Results:, Seventeen patients were in CTP class A, 27 patients in class B, and 9 patients in class C. The median follow-up duration was 24 months. There was single 30-day postoperative mortality in class C, and no CTP class deterioration after 30 days of operation. There was no mortality or recurrences in 17 patients with medically refractory ascites. The difference in 30-day mortality according to CTP class and the presence of refractory ascites did not show statistical significance (P = 0.17 and 0.97, respectively). Conclusion:, Hernia operation could be done safely in CTP class A and B with low rate of recurrences, and there was no definitive increase in the operative risk in class C. In addition, refractory ascites did not increase operative risk and recurrence rate. Therefore, surgical repair might be recommended even in patients with refractory ascites and poor hepatic function to prevent life-threatening complications or severe pain. [source]

Increasing frequency of Gram-positive bacteria in spontaneous bacterial peritonitis

LIVER INTERNATIONAL, Issue 1 2005
Evangelos Cholongitas
Abstract: Aim: To evaluate the characteristics and possible recent changes of the microbial causes of spontaneous bacterial peritonitis (SBP) in cirrhotic patients. Methods: We retrospectively evaluated 42 cirrhotic patients with positive ascitic fluid culture and without evidence of secondary peritonitis who were admitted consecutively to our Department between 1998 and 2002. Results: Twenty (48%) of 42 patients with positive ascitic fluid culture were diagnosed during 1998,1999 (period A) and the remaining 22 (52%) patients during 2000,2002 (period B). Gram-negative bacteria were the cause of SBP in 15 (75%) of the 20 patients during period A and in only nine (41%) of the 22 patients during period B (P=0.026). SBP patients with Gram-positive bacteria compared with those with Gram-negative bacteria were less frequently in Child class C (P=0.058) and had significantly higher ascitic fluid protein (P=0.014) and albumin concentrations (P=0.009) and lower ascitic fluid neutrophil count (P=0.008). Resistance to quinolones was detected significantly more frequently in the isolated Gram-positive than Gram-negative bacteria (P<0.001). Conclusion: Culture-positive SBP in cirrhotic patients are caused more frequently by Gram-positive bacteria during the recent years, which are, in their vast majority, resistant to quinolones. [source]

Clinical improvement in patients with decompensated liver disease caused by hepatitis B after treatment with lamivudine

LIVER TRANSPLANTATION, Issue 6 2000
Craig A. Sponseller
Lamivudine is effective in inhibiting hepatitis B virus (HBV) replication, and its clinical use in patients with chronic hepatitis B is associated with improvements in serum aminotransferase levels and liver histopathologic characteristics. Few data are available on its use in patients with advanced liver disease. We report on the outcomes of 5 patients with hepatic decompensation caused by chronic hepatitis B treated long term with lamivudine. All patients were adult white men seropositive for hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) before therapy. All 5 patients had biopsy-proven cirrhosis with clinical and biochemical evidence of hepatic decompensation. Two patients had Child's class C cirrhosis; 2 patients, class B; and 1 patient, class A (although this patient had persistent portasystemic encephalopathy and developed variceal bleeding). HBV DNA became undetectable in all patients and remained so throughout the study. Both patients with Child's class C and 1 patient with class B cirrhosis had significant clinical improvement. Child-Pugh scores improved from 12 to 7 and 11 to 7 in the 2 patients with Child's class C cirrhosis, and the patient with class B cirrhosis had complete resolution of troublesome encephalopathy. Serum aminotransferase, albumin, and total bilirubin levels improved significantly in 3 of 5 patients. One patient with Child's class B cirrhosis underwent orthotopic liver transplantation at week 13 after dramatic increases in liver tests and clinical worsening. The patient subsequently cleared HBeAg and HBsAg from serum posttransplantation. In conclusion, prolonged therapy with lamivudine resulted in improved serum biochemical values and loss of HBV DNA in patients with decompensated cirrhosis. Clinical improvements, reflected in Child-Pugh classification and functional status, may also occur, particularly among those with Child's class C disease initially. [source]

Re-examining the role of Lys67 in class C ,-lactamase catalysis

PROTEIN SCIENCE, Issue 3 2009
Yu Chen
Abstract Lys67 is essential for the hydrolysis reaction mediated by class C ,-lactamases. Its exact catalytic role lies at the center of several different proposed reaction mechanisms, particularly for the deacylation step, and has been intensely debated. Whereas a conjugate base hypothesis postulates that a neutral Lys67 and Tyr150 act together to deprotonate the deacylating water, previous experiments on the K67R mutants of class C ,-lactamases suggested that the role of Lys67 in deacylation is mainly electrostatic, with only a 2- to 3-fold decrease in the rate of the mutant vs the wild type enzyme. Using the Class C ,-lactamase AmpC, we have reinvestigated the activity of this K67R mutant enzyme, using biochemical and structural studies. Both the rates of acylation and deacylation were affected in the AmpC K67R mutant, with a 61-fold decrease in kcat, the deacylation rate. We have determined the structure of the K67R mutant by X-ray crystallography both in apo and transition state-analog complexed forms, and observed only minimal conformational changes in the catalytic residues relative to the wild type. These results suggest that the arginine side chain is unable to play the same catalytic role as Lys67 in either the acylation or deacylation reactions catalyzed by AmpC. Therefore, the activity of this mutant can not be used to discredit the conjugate base hypothesis as previously concluded, although the reaction catalyzed by the K67R mutant itself likely proceeds by an alternative mechanism. Indeed, a manifold of mechanisms may contribute to hydrolysis in class C ,-lactamases, depending on the enzyme (wt or mutant) and the substrate, explaining why different mutants and substrates seem to support different pathways. For the WT enzyme itself, the conjugate base mechanism may be well favored. [source]

Crystallization and preliminary X-ray crystallographic analyses of CMY-1 and CMY-10, plasmidic class C ,-lactamases with extended substrate spectrum

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 2 2004
Sun-Joo Lee
Plasmid-encoded class C ,-lactamases, including CMY-1 and CMY-­10, hydrolyze the lactam bonds of ,-lactam antibiotics, inducing therapeutic failure and a lack of eradication of clinical isolates by third-generation cephalosporins or cephamycins. Therefore, the enzymes are potential targets for developing agents against pathogens isolated from patients suffering from wound infection, urinary tract infection or pneumonia. CMY-1 and CMY-10 were purified and crystallized at 298,K. X-ray diffraction data from CMY-1 and CMY-­10 crystals have been collected to 2.5 and 1.5,Å resolution, respectively, using synchrotron radiation. The crystals of the two proteins are isomorphous and belong to the primitive monoclinic space group P21. [source]

Expression, purification, crystallization and preliminary X-ray analysis of the native class C ,-­lactamase from Enterobacter cloacae 908R and two mutants

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2001
J. Wouters
Crystals have been obtained of the Enterobacter cloacae 908R ,-­lactamase and two point mutants by the vapour-diffusion method using similar conditions [pH 9.0, polyethylene glycol (Mr = 6000) as precipitant]. The three crystal forms belong to the orthorhombic space group P21212, with roughly the same unit-cell parameters; i.e. for the wild-type crystals a = 46.46, b = 82.96, c = 95.31,Å. In the best cases, the crystals diffract to about 2.1,Å resolution on a rotating-anode X-ray source at room temperature. Co-crystallization experiments of poor substrates with the wild-type protein and the active-site serine mutant (S64C) are planned and should lead to a better understanding of the catalytic mechanism of class C ,-lactamases. [source]

Purification, crystallization and preliminary crystallographic analysis of Est-Y29: a novel oligomeric ,-lactamase

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2009
SeungBum Kim
,-Lactam antibiotics such as penicillins and cephalosporins have a four-atom ring as a common element in their structure. The ,-lactamases, which catalyze the inactivation of these antibiotics, are of great interest because of their high incidence in pathogenic bacteria. A novel oligomeric class C ,-lactamase (Est-Y29) from a metagenomic library was expressed, purified and crystallized. The recombinant protein was expressed in Escherichia coli with an N-terminal 6×His tag and purified to homogeneity. EstY-29 was crystallized and X-ray intensity data were collected to 1.49,Å resolution using synchrotron radiation. [source]

Structure of the plasmid-mediated class C ,-lactamase ACT-1

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2008
Akiko Shimizu-Ibuka
The crystallographic structure of ACT-1, which is the first plasmid-mediated AmpC-type ,-lactamase to have been completely analyzed in terms of nucleotide sequence and which has a high degree of sequence similarity to the chromosomal AmpC enzymes of Enterobacter cloacae and the plasmid-encoded MIR-1, has been solved at 2.4,Å resolution. The overall structure of ACT-1 is similar to those of other class C ,-lactamases, such as the AmpC enzymes from E. cloacae P99 and Escherichia coli. [source]

Volatile Methyl Esters of Medium Chain Length from the Bacterium Chitinophaga Fx7914

CHEMISTRY & BIODIVERSITY, Issue 9 2010
Thorben Nawrath
Abstract The analysis of the volatiles released by the novel bacterial isolate Chitinophaga Fx7914 revealed the presence of ca. 200 compounds including different methyl esters. These esters comprise monomethyl- and dimethyl-branched, saturated, and unsaturated fatty acid methyl esters that have not been described as bacterial volatiles before. More than 30 esters of medium C-chain length were identified, which belong to five main classes, methyl (S)-2-methylalkanoates (class A), methyl (S)-2,(,,1)-dimethylalkanoates (class B), methyl 2,(,,2)-dimethylalkanoates (class C), methyl (E)-2-methylalk-2-enoates (class D), and methyl (E)-2,(,,1)-dimethylalk-2-enoates (class E). The structures of the compounds were verified by GC/MS analysis and synthesis of the target compounds as methyl (S)-2-methyloctanoate (28), methyl (S)-2,7-dimethyloctanoate ((S)- 43), methyl 2,6-dimethyloctanoate (49), methyl (E)-2-methylnon-2-enoate (20a), and methyl (E)-2,7-dimethyloct-2-enoate (41a). Furthermore, the natural saturated 2-methyl-branched methyl esters showed (S)-configuration as confirmed by GC/MS experiments using chiral phases. Additionally, the biosynthetic pathway leading to the methyl esters was investigated by feeding experiments with labeled precursors. The Me group at C(2) is introduced by propanoate incorporation, while the methyl ester is formed from the respective carboxylic acid by a methyltransferase using S -adenosylmethionine (SAM). [source]