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Enzyme Action (enzyme + action)
Selected AbstractsNBT-PABA test to assess efficiency and kinetics of substituted proteolytic enzyme action in pancreatic duct ligated minipigs,JOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 3 2008A. Mößeler Summary The NBT-PABA test is an established method for diagnosis of pancreatic exocrine insufficiency. In the present study the NBT-PABA test was used to test and compare the efficacy of two multienzyme preparations (product A and B) differing in galenic preparation in minipigs in which pancreatic exocrine insufficiency (PEI) was induced by pancreatic duct ligation. Without enzyme substitution no distinct increase in PABA was found in blood after oral administration of NBT-PABA. Administration of both enzyme preparations led to a clear dose dependent rise in PABA-concentrations in blood. Interestingly, the two preparations showed different time curves of serum PABA concentration, indicating differences in the kinetic of proteolytic enzyme action. It is concluded that the NBT-PABA test can be a very useful test for indirectly evaluating proteolytic enzyme efficacy in vivo, and also gives information about the kinetics of enzyme action, not only the end-result of enzyme action (like digestibility trials which were used traditionally). A single test is performed in a few hours and there is no need for fistulated animals. [source] The carboxyl-terminal linker is important for chemoreceptor functionMOLECULAR MICROBIOLOGY, Issue 2 2006Mingshan Li Summary Sensory adaptation in bacterial chemotaxis is mediated by chemoreceptor methylation and demethylation. In Escherichia coli, methyltransferase CheR and methylesterase CheB bind both substrate sites and a carboxyl-terminal pentapeptide sequence carried by certain receptors. Pentapeptide binding enhances enzyme action, an enhancement required for effective adaptation and chemotaxis. Pentapeptides are linked to the conserved body of chemoreceptors through a notably variable sequence of 30,35 residues. We created nested deletions from the distal end of this linker in chemoreceptor Tar. Chemotaxis was eliminated by deletion of 20,40 residues and reduced by shorter deletions. This did not reflect generalized disruption, because all but the most extremely truncated receptors activated kinase, were substrates for adaptational modification and performed transmembrane signalling. In contrast, linker truncations reduced rates of adaptational modification in parallel with chemotaxis. We concluded the linker is important for chemotaxis because of its role in adaptational modification. Effects of linker truncations on CheR binding to receptor-borne pentapeptide implied linker (i) makes pentapeptide available to modification enzymes by separation from the helical receptor body, and (ii) is a flexible arm allowing dual binding of enzyme to pentapeptide and modification site. The data suggest linker and the helix from which it emerges are structurally dynamic. [source] Mycobacterium tuberculosis pantothenate kinase: possible changes in location of ligands during enzyme actionACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009Bhaskar Chetnani The crystal structures of complexes of Mycobacterium tuberculosis pantothenate kinase with the following ligands have been determined: (i) citrate; (ii) the nonhydrolysable ATP analogue AMPPCP and pantothenate (the initiation complex); (iii) ADP and phosphopantothenate resulting from phosphorylation of pantothenate by ATP in the crystal (the end complex); (iv) ATP and ADP, each with half occupancy, resulting from a quick soak of crystals in ATP (the intermediate complex); (v) CoA; (vi) ADP prepared by soaking and cocrystallization, which turned out to have identical structures, and (vii) ADP and pantothenate. Solution studies on CoA binding and catalytic activity have also been carried out. Unlike in the case of the homologous Escherichia coli enzyme, AMPPCP and ADP occupy different, though overlapping, locations in the respective complexes; the same is true of pantothenate in the initiation complex and phosphopantothenate in the end complex. The binding site of MtPanK is substantially preformed, while that of EcPanK exhibits considerable plasticity. The difference in the behaviour of the E. coli and M. tuberculosis enzymes could be explained in terms of changes in local structure resulting from substitutions. It is unusual for two homologous enzymes to exhibit such striking differences in action. Therefore, the results have to be treated with caution. However, the changes in the locations of ligands exhibited by M. tuberculosis pantothenate kinase are remarkable and novel. [source] The Role of Biotechnology in Modern Food ProductionJOURNAL OF FOOD SCIENCE, Issue 3 2004CHERL-HO LEE ABSTRACT: Modern food production technology is given great challenges by the emerging fields of biotechnology and molecular biology. Knowledge of conventional fermentation technology is upgraded by the gene level explanations of enzyme actions and physiological functions of biomaterials derived therefrom. The use of genetically modified organisms (GMOs) and their products in food widens the availability of resources while also raising public interest about safety and labeling. As an example of the application of molecular biology in conventional fermentation technology the selection of proteases from a Bacillus species grown in Korean traditional soybean fermentation starter, Meju, and the production of peptides with blood cholesterol lowering effect, obtained from soybean protein hydrolysate, are presented. Recent developments in the Korean bioindustry are reviewed as an example of the role of biotechnology in the food industry. The present status of GMO enzymes in food production is reviewed and safety issues about GMO use in the food system are discussed. [source] Oxidation by mushroom tyrosinase of monophenols generating slightly unstable o -quinonesFEBS JOURNAL, Issue 19 2000Lorena G. Fenoll Tyrosinase can act on monophenols because of the mixture of mettyrosinase (Em) and oxytyrosinase (Eox) that exists in the native form of the enzyme. The latter form is active on monophenols although the former is not. However, the kinetics are complicated because monophenols can bind to both enzyme forms. This situation becomes even more complex as the products of the enzymatic reaction, the o -quinones, are unstable and continue evolving to generate o -diphenols in the medium. In the case of substrates such as 4-methoxyphenol, 4-ethoxyphenol and 4- tert -butylphenol, tyrosinase generates o -quinones which become unstable with small constants of approximately < 10,3 s,1. The system evolves from an initial steady state, reached when t,0, through a transition state towards a final steady state, which is never reached because the substrate is largely consumed. The mechanisms proposed to explain the enzyme's action can be differentiated by the kinetics of the first steady state. The results suggest that tyrosinase hydroxylates monophenols to o -diphenols, generating an intermediate Em -diphenol in the process, which may oxidize the o -diphenol or release it directly into the medium. In the case of o -quinone formation, its slow instability generates o -diphenol which activates the enzymatic system yielding parabolic time recordings. [source] | |||||||||||||