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71.
72.
Cholinephosphotransferase (EC 2.7.8.2) catalyzes the formation of a phosphoester bond via the transfer of a phosphocholine moiety from CDP-choline to diacylglycerol forming phosphatidylcholine and releasing CMP. A motif, Asp113-Gly114-(X)2-Ala117-Arg118-(X)8-Gly127+ ++-(X)3-Asp131-(X)3-Asp135, located within the CDP-choline binding region of Saccharomyces cerevisiae cholinephosphotransferase (CPT1 ?/Author: Please confirm that a gene is meant here.) is also found in several other phospholipid synthesizing enzymes that catalyze the formation of a phosphoester bond utilizing a CDP-alcohol and a second alcohol as substrates. To determine if this motif is diagnostic of the above reaction type scanning alanine mutagenesis of the conserved residues within S. cerevisiae cholinephosphotransferase was performed. Enzyme activity was assessed in vitro using a mixed micelle enzyme assay and in vivo by determining the ability of the mutant enzymes to restore phosphatidylcholine synthesis from radiolabeled choline in an S. cerevisiae strain devoid of endogenous cholinephosphotransferase activity. Alanine mutants of Gly114, Gly127, Asp131, and Asp135 were inactive; mutants, Ala117 and Arg118 displayed reduced enzyme activity, and Asp113 displayed wild type activity. The analysis described is the first molecular characterization of a CDP-alcohol phosphotransferase motif and results predict a catalytic role utilizing a general base reaction proceeding through Asp131 or Asp135 via a direct nucleophilic attack of the hydroxyl of diacylglyerol on the phosphoester bond of CDP-choline that does not proceed via an enzyme bound intermediate. Residues Ala117 and Arg118 do not participate directly in catalysis but are likely involved in substrate binding or positioning with Arg118 predicted to associate with a phosphate moiety of CDP-choline. 相似文献
73.
Domenico Ferrari 《Multimedia Systems》1998,6(3):179-185
The research done by the Tenet Group in multimedia networking has reached a point where it may be useful to reflect on the
significance of its results for the current debate on how integrated-services internetworks should be designed. Such reflections
constitute the main subject of this paper. The principles of the work and the conclusions reached so far by the Tenet researchers
are discussed in the light of the conflict between the two major technologies being proposed to build future information infrastructures:
namely, the Internet and the ATM technologies. The Tenet approach suggests one feasible way for resolving the conflict to
the advantage of all the users of those infrastructures. This paper discusses various fundamental aspects of integrated-services
network design: the choice of the service model, the type of charging policy to be adopted, and the selection of a suitable
architecture. 相似文献
74.
P Eiselt BS Kim B Chacko B Isenberg MC Peters KG Greene WD Roland AB Loebsack KJ Burg C Culberson CR Halberstadt WD Holder DJ Mooney 《Canadian Metallurgical Quarterly》1998,14(1):134-140
Apoptosis associated oligonucleosomal fragmentation of DNA can result from the activation of endonucleases that exhibit different pH optima and are either sensitive or insensitive to divalent cations. DNA fragmentation due to activation of cation sensitive endonucleases occurs in the absence of a change in intracellular pH whereas intracellular acidification is a feature of apoptosis characterized by activation of cation insensitive acidic endonuclease. We have reported earlier that somatostatin (SST) induced DNA fragmentation and apoptosis is signaled in a receptor subtype selective manner uniquely via human somatostatin receptor subtype 3 (hSSTR3). In the present study we investigated the pH dependence and cation sensitivity of endonuclease induced in hSSTR3 expressing CHO-K1 cells by the SST agonist octreotide (OCT) and its effect on intracellular pH. We show that OCT induced apoptosis is associated with selective stimulation of a divalent cation insensitive acidic endonuclease. The intracellular pH of of cells undergoing OCT induced apoptosis was 0.9 pH units lower than that of control cells. The effect of OCT on endonuclease and pH was inhibited by orthovanadate as well as by pretreatment with pertussis toxin, suggesting that hSSTR3 initiated cytotoxic signaling is protein tyrosine phosphatase mediated and is G protein dependent. These findings suggest that intracellular acidification and activation of acidic endonuclease mediate wild type p53 associated apoptosis signaled by hormones acting via G protein coupled receptors. 相似文献
75.
76.
CR Dudley B Keavney IM Stratton RC Turner PJ Ratcliffe 《Canadian Metallurgical Quarterly》1995,48(6):1907-1911
We performed a case-control study to determine whether molecular variants of genes of the renin-angiotensin system were associated with the presence of albuminuria in non-insulin dependent diabetes mellitus (NIDDM). A total of 180 diabetic patients with persistent microalbuminuria [median urinary albumin (interquartile range) of 74 (54 to 126 mg/liter)] were matched with two control groups of diabetic patients without microalbuminuria [median urinary albumin 7 (5 to 10) mg/liter] for variables known to be associated with raised urinary albumin concentration including hemoglobin A1c and triglyceride. One control group was also matched for blood pressure and the other group was not, to allow assessment of interactions with hypertension. Association with the I/D polymorphism of the ACE gene and M235T variant of the angiotensinogen gene (AGT) with microalbuminuria and retinopathy was examined. There were no significant differences in genotype frequency between cases and controls for ACE or AGT irrespective of blood pressure matching. However, among subjects with microalbuminuria, those with the ACE DD genotype had a significantly greater urinary albumin excretion than individuals with a non-DD genotype [median 88 (68 to 170) mg/liter vs. 67 (53 to 113) mg/liter, P < 0.001]. More subjects with the DD than non-DD genotype had persistent albuminuria > 100 mg/liter, twice the upper normal range (60% vs. 38%, P = 0.006). When increased albumin excretion occurs, the presence of the ACE DD genotype appears to be associated with higher urinary albumin levels. No association with retinopathy was observed. 相似文献
77.
78.
Concurrent infection is a risk factor for abdominal wound dehiscence. We reviewed our experience with fascial dehiscence to determine the incidence and to identify prognostic factors for associated intra-abdominal infection. Over a 7-year period, 107 patients with abdominal wound dehiscence were identified. Seventeen were managed nonoperatively, and 90 underwent exploratory laparotomy, 43 of whom had no intra-abdominal pathology and 47 of whom had intra-abdominal infections. Demographic factors, comorbid diseases, and potential indicators of systemic infection did not distinguish patients with intra-abdominal infection from those without. Patients with an intra-abdominal infection were more likely to have undergone an emergency operation (74% vs 48%; P < 0.02), an operation on the colon (55% vs 25%; P < 0.005), or an operation with a higher wound classification (P < 0.02). Mortality was higher in patients with intra-abdominal infection than in those without (44% vs 20%; P < 0.02). Wound dehiscence after emergent operations, and operations with a higher wound classification, especially those involving the colon, should raise concern for intra-abdominal infection. Thorough abdominal exploration should be performed at the time of dehiscence repair. Before nonoperative management is chosen, intra-abdominal infection should be excluded. 相似文献
79.
Recursive algorithms for implementing digital image filters 总被引:1,自引:0,他引:1
Ferrari LA Sankar PV Shinnaka S Sklansky J 《IEEE transactions on pattern analysis and machine intelligence》1987,(3):461-466
The B-spline functions are used to develop recursive algorithms for the efficient implementation of two-dimensional linear digital image filters. These filters may be spatially varying. The B-splines are used in a representation of the desired point spread function. We show that this leads to recursive algorithms and hardware implementations which are more efficient than either direct spatial domain filter realizations or FFT implementations. The Z-transform is used to develop a discrete version of Duhamel's theorem. A computer architecture for B-spline image filters is proposed and a complexity analysis and comparison to other approaches is provided. 相似文献
80.
Giuseppe Placidi Danilo Avola Marco Ferrari Daniela Iacoviello Andrea Petracca Valentina Quaresima Matteo Spezialetti 《Computer methods and programs in biomedicine》2014