Enzyme value, definition

Enzyme, diagram of postulated union of substrate with, V, 56 Enzyme specificity, principles underlying, in the domain of carbohydrates, V, 49-78 Enzyme value, definition, V, 62 comparative values from rates of hydrolysis of phenyl hexosides and pentosides, V, 62... 

For biochemical reactions in which hydrogen ions (H ) are consumed or produced, the usual definition of the standard state is awkward. Standard state for the ion is 1 M, which corresponds to pH 0. At this pH, nearly all enzymes would be denatured, and biological reactions could not occur. It makes more sense to use free energies and equilibrium constants determined at pH 7. Biochemists have thus adopted a modified standard state, designated with prime ( ) symbols, as in AG°, AH°, and so on. For values determined... 

Although there was a decreasing trend noted throughout the harvest period in the pectin content of the composite must samples, there was no definite trend in the pectin values for the must at zero time (no enzyme treatment). Variation was apparent from season to season as well as throughout a given season. 

Calculation of the Endocellulase Activity from the Intrinsic Viscosity Values. The enzymic degradation of polymeric substrates can occur at different bonds in the same substrate molecule, and the enzymic activity has to be defined here as the initial number of moles of glyco-sidic bonds split per second (53). This definition corresponds to the definition of the katal, symbolyzed kat. This unit is defined as the catalytic amount of any catalyst (including any enzyme) that catalyzes a reaction rate of one mole per second in an assay system (54), and it is recommended by the International Union of Pure and Applied Chemistry (55) for the quantitative evaluation of catalytic activities. 

Enzymatic reactions coupled to optical detection of the product of the enzymatic reaction have been developed and successfully used as reversible optical biosensors. By definition, these are again steady-state sensors in which the information about the concentration of the analyte is derived from the measurement of the steady-state value of a product or a substrate involved in highly selective enzymatic reaction. Unlike the amperometric counterpart, the sensor itself does not consume or produce any of the species involved in the enzymatic reaction it is a zero-flux boundary sensor. In other words, it operates as, and suffers from, the same problems as the potentiometric enzyme sensor (Section 6.2.1) or the enzyme thermistor (Section 3.1). It is governed by the same diffusion-reaction mechanism (Chapter 2) and suffers from similar limitations. 

The affinity with which an inhibitor binds to an enzyme is defined by its A) value, whereas the affinity with which the substrate binds is generally defined by its Km value. Both definitions are somewhat simplistic as they are based on three assumptions ... 

In a study of the highly purified alanine racemase of E. coli, Lambert and Neuhaus determined significant differences in the maximal velocities and the Michaelis-Menten constants of the substrates in the forward (L - dl) and reverse directions (d - dl) [37]. From these data the value calculated for Keq is 1.11 0.15. The time course of the reaction showed that in 10 min with L-alanine as substrate ca. 0.09 jumol of D-alanine were formed. With the same amount of enzyme (750 ng) and in the same time period, ca. 0.05 jamol of L-alanine were formed from D-alanine. Similar results have been reported for the same enzyme from S. faecalis and for proline racemases [37]. Thus, in these cases, there are definite kinetic differences, as expected for the existence of two diastereoisomers formed between enzyme and two substrate enantiomers. 

Mathematical optimization deals with determining values for a set of unknown variables x, X2, , x , which best satisfy (optimize) some mathematical objective quantified by a scalar function of the unknown variables, F(xi, X2, , xn). The function F is termed the objective function bounds on the variables, along with mathematical dependencies between them, are termed constraints. Constraint-based analysis of metabolic systems requires definition of the constraints acting on biochemical variables (fluxes, concentrations, enzyme activities) and determining appropriate objective functions useful in determining the behavior of metabolic systems. 

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