Subject partially irreversible

How do materials behave when they are subjected to forces which act upon them The resulting deformation can be 1) reversible as soon as the forces are removed, the deformation is completely undone. In this case there is question of an elastic deformation 2) completely or partially irreversible when the forces are removed, the... 

Altered platelet numbers and function Platelet dysfunction occurs dose-dependently with carbenicillin, ticarcillin, and, infrequently, other broad-spectrum penicillins (105), but the NMTT cephalosporin moxalactam has also been associated with altered platelet function in both healthy subjects and in patients treated with standard regimens (106-110). In contrast, clinical studies including cefotaxime, ceftizoxime, cefoperazone, and ceftracone did not show platelet dysfunction attributable to these compounds (109-111). There is evidence that beta-lactam-antibiotic-induced platelet dysfunction is at least partially irreversible (112). 

The subject of kinetics is often subdivided into two parts a) transport, b) reaction. Placing transport in the first place is understandable in view of its simpler concepts. Matter is transported through space without a change in its chemical identity. The formal theory of transport is based on a simple mathematical concept and expressed in the linear flux equations. In its simplest version, a linear partial differential equation (Pick s second law) is obtained for the irreversible process, Under steady state conditions, it is identical to the Laplace equation in potential theory, which encompasses the idea of a field at a given location in space which acts upon matter only locally Le, by its immediate surroundings. This, however, does not mean that the mathematical solutions to the differential equations with any given boundary conditions are simple. On the contrary, analytical solutions are rather the, exception for real systems [J. Crank (1970)]. 

The preceding experiments prove that there is an intermediate on the reaction pathway in each case, the measured rate constants for the formation and decay of the intermediate are at least as high as the value of kcat for the hydrolysis of the ester in the steady state. They do not, however, prove what the intermediate is. The evidence for covalent modification of Ser-195 of the enzyme stems from the early experiments on the irreversible inhibition of the enzyme by organo-phosphates such as diisopropyl fluorophosphate the inhibited protein was subjected to partial hydrolysis, and the peptide containing the phosphate ester was isolated and shown to be esterified on Ser-195.1516 The ultimate characterization of acylenzymes has come from x-ray diffraction studies of nonspecific acylenzymes at low pH, where they are stable (e.g., indolylacryloyl-chymotrypsin),17 and of specific acylenzymes at subzero temperatures and at low pH.18 When stable solutions of acylenzymes are restored to conditions under which they are unstable, they are found to react at the required rate. These experiments thus prove that the acylenzyme does occur on the reaction pathway. They do not rule out, however, the possibility that there are further intermediates. For example, they do not rule out an initial acylation on His-57 followed by rapid intramolecular transfer. Evidence concerning this and any other hypothetical intermediates must come from additional kinetic experiments and examination of the crystal structure of the enzyme. 

The ability of adenine and cytosine to undergo reduction in aqueous medium is at least partially retained at the level of oligo- and polynucleotides. In both acid and neutral media, such residues in single-stranded RNA, DNA and synthetic polynucleotides, when subjected to d.c. polarography, undergo irreversible reduction in a protonated, adsorbed, state with the transfer of four electrons to adenine... 

Bresnick (52) has concluded that in the partially hepatectomized rat, during the first 12 hours of liver regeneration, the activity of orotate phosphoribosyltransferase determines the rate of synthesis of the uridine phosphates. The potential activity of orotidylate decarboxylase is in excess of that of orotate phosphoribosyltransferase. This probably accounts for the virtual absence of orotidylate in animal tissues. The decarboxylation step is irreversible and may be subject to feedback inhibition by uridylate, which is a competitive inhibitor of the enzyme in rat liver and yeast (19). 

GuTifiRREZ-MARTfN et al. (2002) simulated chronic exposure to OONO" by treatment of mt brain synaptosomes or plasma membrane vesicles with repetitive pulses of OONO" during at most 50 min, which efficiently produced nitrotyrosine formation in several membrane proteins including the Ca " -ATPase. The plasma membrane Ca -ATPase activity at near-physiological conditions (pH 7, submicromolar Ca, and millimolar Mg -ATP concentrations), which plays a major role in the control of synaptic [Ca ji, could be more than 75 % inhibited by a sustained exposure to micromolar OONO (e.g., to 100 pulses of lOjuM OONO ). This inhibition was irreversible and mostly due to decreased and to a 2-fold increase of the K0 5 for Ca stimulation and about 5-fold increase of the Km for Mg -ATP. [Ca ji increased to >400 nM when synaptosomes were subjected to this treatment. Reduced glutathione could afford only partial protection against the inhibition produced by micromolar OONO pulses. 

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