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1,2-Dithiole-3-Ones as Potent Inhibitors of the Bacterial 3-Ketoacyl Acyl Carrier Protein Synthase III (FabH). Xin He, 2004.The enzyme FabH catalyzes the initial step of fatty acid biosynthesis via a type II dissociated fatty acid synthase . The pivotal role of this essential enzyme, combined with its unique structural features and ubiquitous occurrence in bacteria, has made it an attractive new target for the development of antibacterial and antiparasitic compounds . We have searched the National Cancer Institute database for compounds bearing structural similarities to thiolactomycin, a natural product which exhibits a weak activity against FabH . This search has yielded several substituted 1,2-dithiole-3-ones that are potent inhibitors of FabH from both Escherichia coli (ecFabH) and Staphylococcus aureus (saFabH) . The most potent inhibitor was 4,5-dichloro-1,2-dithiole-3-one, which had 50% inhibitory concentration (IC50) values of 2 µM (ecFabH) and 0.16 µM (saFabH) . The corresponding 3-thione analog exhibited comparable activities . Analogs in which the 4-chloro substituent was replaced with a phenyl group were also potent inhibitors, albeit somewhat less effectively (IC50 values of 5.7 and 0.98 µM for ecFabH and saFabH, respectively) . All of the 5-chlorinated inhibitors were most effective when they were preincubated with FabH in the absence of substrates . The resulting enzyme-inhibitor complex did not readily regain activity after excess inhibitor was removed, suggesting that a slow dissociation occurs . In stark contrast, a series of inhibitors in which the 5-chloro substituent was replaced with the isosteric and isoelectronic trifluoromethyl group were poorer inhibitors (IC50 values typically ranging from 25 to >100 µM for both ecFabH and saFabH), did not require a preincubation period for maximal activity, and generated an enzyme-inhibitor complex which readily dissociated . Possible modes of binding of 5-chloro-1,2-dithiole-3-ones and 5-chloro-1,2-dithiole-3-thiones with FabH which account for the role of the 5-chloro substituent were considered . Properties of a Novel Thermostable Glucoamylase from the Hyperthermophilic Archaeon Sulfolobus solfataricus in Relation to Starch Processing. Mi-Sun Kim, 2004.A gene (ssg) encoding a putative glucoamylase in a hyperthermophilic archaeon, Sulfolobus solfataricus, was cloned and expressed in Escherichia coli, and the properties of the recombinant protein were examined in relation to the glucose production process . The recombinant glucoamylase was extremely thermostable, with an optimal temperature at 90°C . The enzyme was most active in the pH range from 5.5 to 6.0 . The enzyme liberated ß-D-glucose from the substrate maltotriose, and the substrate preference for maltotriose distinguished this enzyme from fungal glucoamylases . Gel permeation chromatography and sedimentation equilibrium analytical ultracentrifugation analysis revealed that the enzyme exists as a tetramer . The reverse reaction of the glucoamylase from S . solfataricus produced significantly less isomaltose than did that of industrial fungal glucoamylase . The glucoamylase from S . solfataricus has excellent potential for improving industrial starch processing by eliminating the need to adjust both pH and temperature . Synthesis and Deformylation of Staphylococcus aureus  -Toxin Are Linked to Tricarboxylic Acid Cycle Activity.Greg A. Somerville, 2003.In bacteria, translation initiates with formyl-methionine; however, the N-terminal formyl group is usually removed by peptide deformylase, an enzymatic activity requiring iron . Staphylococcus aureus -toxin is a 26-amino-acid polypeptide secreted predominantly with a formylated N-terminal methionine, which led us to investigate regulation of
-toxin deformylation . We observed that during exponential and early postexponential growth,
-toxin accumulated in the culture medium in formylated and deformylated forms . In contrast, only formylated
-toxin accumulated after the early postexponential phase . The transition from producing both species of
-toxin to producing only formyl-methionine-containing
-toxin coincided with increased tricarboxylic acid (TCA) cycle activity . The TCA cycle contains several iron-requiring enzymes, which led us to hypothesize that TCA cycle induction depletes the iron in the culture medium, thereby inhibiting peptide deformylase activity . As expected, S . aureus depletes the iron in the culture medium between the postexponential and stationary phases of growth . Inhibition of
-toxin deformylation was relieved by TCA cycle inactivation or by addition of supplemental iron to the culture medium . Of interest, peptides containing formyl-methionine are potent chemoattractants for neutrophils, suggesting that
-toxin deformylation may have functional consequences . We found neutrophil chemotactic activity only with formylated
-toxin . The S . aureus TCA cycle is derepressed upon depletion of rapidly catabolizable carbon sources; this coincides with the transition to producing only formylated
-toxin and results in an increased inflammatory response . The proinflammatory response should increase host cell damage and result in the release of nutrients . Taken together, these results establish that there is an important linkage between bacterial metabolism and pathogenesis .
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