Single turnover

AbouKhair, N. K., Ziegler, M. M., and Baldwin, T. O. (1985). Bacterial luciferase demonstration of a catalytically competent altered conformational state following a single turnover. Biochemistry 24 3942-3947. 

Eckstein, J. W., et al. (1990). A time-dependent bacterial bioluminescence emission spectrum in an in vitro single turnover system energy transfer alone cannot account for the yellow emission of Vibrio fischeri Y-l. Proc. Natl. Acad. Sci. USA 87 1466-1470. 

Details of the mechanism of naphthalene dioxygenase during a single turnover of the enzyme have been revealed, and conhrmed the separate roles of the dioxygenase and the ferredoxin electron transfer protein. This made it possible to propose a reaction cycle for the reaction (Wolfe et al. 2001). 

Wolfe MD, JV Parales, DT Gibson, JD Lipscomb (2001) Single turnover chemistry and regulation of Oj activation by the oxygenase component of naphthalene 1,2-dioxygenase. J Biol Chem 276 1945-1953. 

Both mechanisms can also rationalize an increase in due to the production of superoxide/HO2 (18.16), which appears to dominate the flux of partially reduced oxygen species generated by certain biomimetic catalysts [Boulatov et al., 2002 Boulatov, 2004]. It remains to be estabhshed if either of these two mechanisms does indeed operate in simple Fe porph5Tins, for example by carrying out single-turnover experiments similarly to the approach used to study ORR by C5hochrome c oxidase. 

Collman JP, Decreau RA, Yan Y, Yoon J, Solomon El. 2007a. Intramolecular single-turnover reaction in a cytochrome c oxidase model bearing a Tyr244 mimic. J Am Chem Soc 129 5794. 

D. Yields and Rate Constants with Single Turnover Reactions... 

Protein B from M. capsulatus (Bath) not only increases the product yields, but also influences the rate constant for the single turnover reaction of Hred with nitrobenzene (51,67). The pseudo-first-order rate constant increases up to 33-fold when Hred is titrated with protein B. Neither addition of reductase to Hox or Hred, nor addition of protein B and reductase to Hred, could similarly affect the rate constant. These... 

Protein ALBP-PX was the first pyridoxamine-conjugated protein to be synthesized and structurally characterized. Under single-turnover conditions, this protein demonstrated amino acid production rates of only 56% of the free cofactor. However, depending on the nature of the a-keto acid, ALBP-PX did show a range of optical inductions for the amino acid product. Notably, enantiomeric excesses in the order of 94% were observed for the production of valine. Additionally, several trends were noted. All amino acid products that showed optical induction favored the 1-enantiomer, except alanine, which favored the d-enantiomer. Furthermore, a-keto acids with branched side chains... 

A single turnover study of the conversion of the heme-HO-1 complex to free biliverdin has elucidated the relative rates of the catalytic steps 129). This transient kinetic study indicates that the conversion of Fe heme to Fe verdoheme is biphasic. Electron transfer to the Fe -heme HO-1 complex occurred at a rate of 0.11 s at 4°C and 0.49 s at 25°C with a 0.1 1 ratio of NADPH-cytochrome P450 reductase to heme HO-l complex. Oxygen binding to the reduced iron was sufficiently rapid im-der the experimental conditions that the species actually monitored... 

Fig. 6A,B Titration with ions. The hammerhead ribozyme reaction was examined on a background of ions A data obtained by Lott et al. [54]. The proposed binding of metal ions is illustrated B data obtained by Nakamatsu et al. [87]. An unmodified ribozyme (R34 gray curve) and a modified ribozyme (7-deaza-R34 black curve) were used. The rate constants were normalized by reference to the maximum rate constant ([La ]=3 (mol/1). Reactions were performed under single-turnover conditions in the presence of 80 nmol/1 ribozyme and 40 nmol/1 substrate at 37 °C...

White et aP measured the rates of phosphate release during a single turnover of actomyosin nucleoside triphosphate (NTP) hydrolysis using a double-mixing stopped-flow spectrofluorometer, at very low ionic strength to increase the affinity of myosin-ATP and myo-sin-ADP-Pi to actin. Myosin subfragment 1 and a series of nucleoside triphosphates were mixed and incubated for approximately 1-10 s to allow NTP to bind to myosin and generate a steady-state mixture of myosin-NTP and myosin-NDP-Pi. The steady-state intermediates were then mixed with actin. 

Reaction conditions that only permit a catalyst to pass through a single round of catalysis. Single-turnover conditions are usually obtained by limiting the substrate concentration relative to the concentration of active catalyst. Occasionally, single-turnover conditions can also be achieved by limiting the period of reaction. 

Johnson and Fierke Hammes have presented detailed accounts of how rapid reaction techniques allow one to analyze enzymic catalysis in terms of pre-steady-state events, single-turnover kinetics, substrate channeling, internal equilibria, and kinetic partitioning. See Chemical Kinetics Stopped-Flow Techniques... 

OXYGEN, OXIDES 0X0 ANIONS SINGLET STATE JABLONSKI DIAGRAM SINGLET-TRIPLET ENERGY TRANSFER SINGLE-TURNOVER CONDITIONS Site-directed inhibitor,... 

Mononuclear octahedral/trigonal bipyramidal iron centers are found in either the ferric or the ferrous oxidation state (Whittaker etal., 1984 Arciero et ai, 1983). Because the iron may participate directly in catalysis as either a Lewis acid or base, only one state is the active form for a given enzyme. Transient redox changes may occur during turnover, but the enzyme returns to its initial condition. In contrast the tetrahedral mononuclear iron proteins appear to function primarily as electron transfer agents and therefore change oxidation state with a single turnover. 

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