Isotope exchange at equilibrium

Computer simulations also point to the regulatory potential of these non-productive complexes. See Deadend Complexes Inhibition Nonproductive Complexes Product Inhibition Substrate Inhibition Isotope Trapping Isotope Exchange at Equilibrium Enzyme Regulation... 

The change in concentration of a molecular entity (being transformed) per unit time and usually symbolized by (f). This change in concentration (/.c., dc/dt) occurs in one direction only and applies to the progress of a reaction step (or sequence of steps) in a complex scheme that may even involve a set of parallel reactions. The term chemical flux can also refer to the progress of a chemical reaction(s) in one direction while that system is at equilibrium (Le., via isotope exchange at equilibrium). 

Constant ratio methods are also employed to maintain mass action ratios in measurements of isotope exchange at equilibrium. 

A potential limitation encountered when one seeks to characterize the kinetic binding order of certain rapid equilibrium enzyme-catalyzed reactions containing specific abortive complexes. Frieden pointed out that initial rate kinetics alone were limited in the ability to distinguish a rapid equilibrium random Bi Bi mechanism from a rapid equilibrium ordered Bi Bi mechanism if the ordered mechanism could also form the EB and EP abortive complexes. Isotope exchange at equilibrium experiments would also be ineffective. However, such a dilemma would be a problem only for those rapid equilibrium enzymes having fccat values less than 30-50 sec h For those rapid equilibrium systems in which kcat is small, Frieden s dilemma necessitates the use of procedures other than standard initial rate kinetics. 

Another important characteristic of ping pong reaction is the presence of exchange reactions in the absence of other substrates. See Isotope Exchange at Equilibrium Multisite Ping Pong Bi Bi Mechanism Half-Reaction Substrate Synergism... 

ISOTOPE EXCHANGE AT EQUILIBRIUM ISOTOPE TRAPPING LACTATE DEHYDROGENASE LIGAND EXCLUSION MODEL NONPRODUCTIVE COMPLEXES PRODUCT INHIBITION SUBSTRATE INHIBITION... 

ISOTOPE EXCHANGE AT EQUILIBRIUM EQUILIBRIUM ISOTOPE EFFEOT ISOTOPE EFFECT... 

ISOTOPE EXCHANGE AT EQUILIBRIUM First-order process/reaction,... 

ISOTOPE EXCHANGE AT EQUILIBRIUM WEDLER-BOYER TECHNIQUE CUMULATIVE INHIBITION UNCONSUMED SUBSTRATE CRYPTIC CATALYSIS BOROHYDRIDE REDUCTION ENZYME CASCADE KINETICS... 

ORDERED Bl Bl ENZYME MECHANISM ISOTOPE EXCHANGE AT EQUILIBRIUM... 

MULTISUBSTRATE MECHANISM Random Bi Bi ternary complex mechanism, ISOTOPE EXCHANGE AT EQUILIBRIUM RANDOM Bl UNI MECHANISM RANDOM Bl UNI UNI Bl PING PONG MECHANISM... 

ISOTOPE EXCHANGE AT EQUILIBRIUM SUBSTRATE PURITY SUBSTRATE STABILITY HANDLING SUBSTRATE SYNERGISM SUBTILISIN... 

Isotope exchange at equilibrium. Consider the reaction of substrates A and B to form P and Q (Eq. 9-51). If both reactants and both products are present with the enzyme and in the ratio found at equilibrium no net reaction will take place. However, the reactants and products will be continually interconverted under the action of the enzyme. Now if a small amount of... 

In the presence of activator, pyruvate, the substrate saturation curves of the R. ruhrum ADP-Glc PPase are hyperbolic at low temperatures. Using kinetic studies its reaction mechanism was studied. The product inhibition patterns eliminated all known sequential mechanisms except the ordered BiBi or Theorell—Chance mechanisms. Small intercept effects suggested the existence of significant concentrations of central transis-tory complexes. Kinetic constants obtained in the study also favored the ordered BiBi mechanism. In addition studies using ATP-[ P]-pyrophosphate isotope exchange at equilibrium supported a sequential-ordered mechanism, which indicated that ATP is the first substrate to bind and that ADP-Glc is the last product to... 

Initial rate measurements, especially with alternative substrates and with a product or substrate analog as inhibitor, and measurements of the rate of isotope exchange at equilibrium, can give a great deal of information about mechanism, and in some cases allow estimates of individual velocity constants and dissociation constants. The results of such studies, which require little enzyme, are an essential basis for the proper interpretation, in relation to the overall catalytic reaction, of pre-steady-state studies and kinetic and thermodynamic studies of enzyme-coenzyme reactions in isolation. 

Silverstein and Boyer 250) used the rate of isotope exchange at equilibrium in the presence of high concentrations of substrates to support a compulsory order mechanism at neutral pH. However, at high pH they suggested the mechanism may only be a preferred order of addition of substrate and coenzyme. 

A method that is potentially very powerful in distinguishing between various candidate mechanisms for an enzyme is that of isotope exchange at equilibrium [68-70], It has been relatively little used, although the principle is elegant, because it is experimentally tedious each piece of information represents many laborious measurements. The principle may be easily illustrated by considering Schemes 8 and... 

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