Measurement of substrates

An important advance on these studies was the possibility of isolating AORs from Fe enriched media with obvious interest for an iron-sulfur center site labeling, with enhanced sensitivity of the Mossbauer studies. The work developed with bacterial systems is advantageous as compared with mammalian systems for isotopic labeling and opens the possibility of a direct measurement of substrate binding. Spectra of the enzyme in oxidized, partially reduced, benzaldehyde-reacted, and fully reduced states were recorded at different temperatures and with variable externally applied magnetic fields (222). In the oxidized enzyme, the clusters are diamag-... 

Gel of polymer around glass electrode Solution of enzyme or of enzyme substrate Enzyme electrode or its substrate electrode H (or OH ) as an indirect measure of substrate or enzyme... 

Fig. 7.5 Time dependence of isotopic ratios in measurements of substrate compositions...

Dupont Y. 1984. A rapid filtration technique for membrane fragments or immobilized enzymes measurements of substrate binding or ion fluxes with a few millisecond time resolution. Anal Biochem 142 504. 

Zero-Trans Procedures These methods involve measurements of substrate transport into or out of a container i.e., a cell, organelle, vesicle, etc.) in which one side of the membrane (the trans side) is free of the... 

Vmax/Km (As Measure of Substrate Capture and Product Release)... 

It is usual therefore to use [MeOAc] as the measure of substrate present in reactor compositions when describing either carbonylation of MeOH to AcOH or MeOAc to AC2O. 

Jefcoate, C.R. (1978) Measurement of substrate and inhibitor binding to microsomal cytochrome P-450 by optical-difference spectroscopy. Methods in Enzymology, 52, 258—279. 

If an enzyme assay involves continuous monitoring of substrate or product concentration, the assay is said to be kinetic. If a single measurement of substrate or product concentration is made after a specified reaction time, a fixed-time assay results. The kinetic assay is more desirable because the time course of the reaction is directly observed and any discrepancy from linearity can be immediately detected. 

Intermediary metabolism of irradiated tissues was examined to attempt to explain the increased respiration on the basis of biochemical mechanics. In these experiments carrot disks 0.5 mm. thick were prepared as before and subjected to substrate utilization studies (9). This involved incubating the slices with the appropriately labeled substrate in 0.03M phospate buffer at 25°C. The incubation involves shaking with gentle aeration and trapping the respired CO2 in alkali. Following incubation the slices were removed, washed, ground with 80% ethanol, and filtered, and both the filtrate and residue were assayed for radioactivity. Thus, a measure of substrate absorption and utilization was determined. 

M. Adami, L. Piras, M. Lanzi, A. Fanigliulo, S. Vakula and C. Nicoli, Monitoring of enzymatic activity and quantitative measurements of substrates by means of a newly designed silicon-based potentiometric sensor, Sens. Actuators B Chem., 18(1-3) (1994) 178-182. 

Typical kinetic analyses of enzyme-substrate systems are based on observed rates of enzyme-catalyzed reactions over a range of enzyme and substrate concentrations. Analyses of this type are commonplace for soluble enzyme-soluble substrate systems in which measures of substrate and... 

Fig. 8 Measurement of substrate structure (same polymer matrix)...

Certain limitations were noted however. First, the plot did not predict the zero value of selectivity for highly unstable ions, expected from the reactivity- selectivity principle. Secondly, as discussed on p. 77, solvolytic rate constants are only a very approximate measure of substrate reactivity. Furthermore, the possibility exists of solvent sorting, in which the concentration of potential nucleophiles around the reaction intermediate differs from that in the bulk solution. Such a phenomenon would, of course, seriously diminish the significance of selectivity as a measure of reactivity, and, while such a possibility... 

The catalytic efficiency of an enzyme is indicated by its kcatIKM value, the value combining the effectiveness of both the productive substrate binding and the subsequent conversion of substrate molecules into product (Copeland, 2000). This value is the apparent second-order rate constant for enzyme action under conditions in which the binding site of the enzyme is largely unoccupied by substrate. The kcatIKM value is the index for comparing the relative rates of cleavage of alternative, competing substrates. The KM is the Michaelis constant, an apparent dissociation constant and hence a measure of substrate affinity. This value equals the concentration of substrate needed to reach half maximum velocity of the enzyme reaction. 

Measurement of substrate surface charge was not performed in this study. A change in surface charge might be expected due to the plasma treatment either by ion implantation or by formation of ionizable functionalities on the substrate surface. 

Sampurno YA, Borucki L, Zhuang Y, Boning D, Philipossian A. A method for direct measurement of substrate temperature during copper CMP. J Electrochem Soc 2005 152(7) G537-G541. 

The data in Table II pertaining to pyrolysis conditions shows that all four feedstocks were pyrolyzed under substantially similar conditions, namely steam-to-hydrocarbon weight ratios of 0.9 0.1, residence times of 0.3 sec, reactor exit pressures of 2.0 bar absolute, and reactor exit temperatures of 835°C. Care also was taken to maintain identical axial temperature profiles in the reactor for each of these runs. No unambiguous measure of substrate conversion during pyrolysis is possible for distillate feedstocks of the type used in the present experiments in terms of the empirical kinetic severity function of Zdonik et al. (5), all of the present experiments were conducted at a severity of about 2. 

FT-RAIRS measurements of CO have also been used to identity facets of oxide supported Cu particles [78, 82]. The low sensitivity of RAIRS on single crystal ZnO(OOOl) prevented the observation of adsorbed CO or CO2, despite their observation in NEXAFS [78], although the local metallic dielectric allowed CO to be observed on the Cu particles. There appear to be no examples of HREELS being used to carry out vibrational spectroscopy of adsorbates on oxide supported metal particles. A HREELS study of Ag on MgO(lOO) films [95] was used only to characterise the Ag induced attenuation in the substrate Fuchs-Kliewer phonons, and the appearance of the metal/oxide interfacial plasmon at higher energies. HREELS has also been used to characterise the oxide/oxide interface between NiO and thin film MgO(lOO) [96]. Similar measurements of substrate phonon attenuation were made in HREELS studies on Pt films grown on ZnO(OOOl) [97]. 

Germer TA, Stephenson JC, Heilweil EJ, Cavanagh RR (1993) Picosecond measurement of substrate-to-adsorbate energy transfer The frustrated translation of CO/Pt(l 11). J Chem Phys 98 9986... 

Voltammetric measurements are not simply restricted to analytical laboratories. The applications of these methods are more numerous than is at first obvious. A large number of analytical instruments, whether portable or not, intended to make precise measurements of substrates present in gas mixtures, vapours or solutions are equipped with electrochemical sensors. These devices operate on the principle of the 2- or 3- electrode cell enclosed in the sensor housing. 

In situ microbial production is potentially the most important source of organic C to buoyant and especially neutrally buoyant plumes (Lilley etal., 1995 Winn etal., 1995 Cowen etal., 2001). However, plume productivity is poorly constrained only limited simultaneous measurements of substrate oxidation rates and C02 incorporation rates have been made in hydrothermal plumes for key substrates. For example, rates of dark C02 assimilation and methane oxidation in plumes from the Manus and Lau basins were found to be relatively high (1200-2500ngC-1 day-1 and 1300ngC 1day 1, respectively), but dropped considerably with increasing distance from the vents (Lein etal., 1997). 

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