scholarly journals Some kinetic properties of the tryptophan-sensitive 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase from Neurospora crassa

1981 ◽  
Vol 199 (3) ◽  
pp. 657-665 ◽  
Author(s):  
G A Nimmo ◽  
J R Coggins
Keyword(s):  
Steady State ◽  
Neurospora Crassa ◽  
Kinetic Properties ◽  
Steady State Kinetic ◽  
Ping Pong ◽  
Rapid Equilibrium ◽  
State Kinetic ◽  
Phosphate Synthase

The steady-state kinetic properties of purified tryptophan-sensitive 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase from Neurospora crassa were examined. The results suggest that the enzyme obeys a Rapid-Equilibrium Ordered mechanism, in which phosphoenolpyruvate is the first substrate to bind and 3-deoxy-D-arabino-heptulosonate 7-phosphate is the second product to be released, rather than a Ping Pong mechanism as has been reported previously. The inhibition by tryptophan was found to be parabolic competitive with respect to D-erythrose 4-phosphate and parabolic non-competitive with respect to phosphoenolpyruvate. The enzyme was inactivated by EDTA, and could be protected against this inactivation by phosphoenolpyruvate or 3-deoxy-D-arabino-heptulosonate 7-phosphate but not by D-erythrose 4-phosphate, tryptophan or Pi. This suggests that the enzyme may be a metalloenzyme.

Pre-steady-state kinetic studies of rat kidneyγ-glutamyl transpeptidase confirm its ping-pong mechanism

2004 ◽  
Vol 17 (67) ◽  
pp. 529-536 ◽  
Author(s):  
Jeffrey W. Keillor ◽  
Annie Ménard ◽  
Roselyne Castonguay ◽  
Christian Lherbet ◽  
Caroline Rivard
Keyword(s):  
Steady State ◽  
Kinetic Studies ◽  
Steady State Kinetic ◽  
Ping Pong ◽  
Glutamyl Transpeptidase ◽  
State Kinetic

Effect of diethyl pyrocarbonate modification on spectral and steady-state kinetic properties of bovine heart cytochrome oxidase

1992 ◽  
Vol 70 (7) ◽  
pp. 565-572
Author(s):  
John D. Doran ◽  
Bruce C. Hill
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Cytochrome Oxidase ◽  
Proton Pumping ◽  
Kinetic Properties ◽  
High Turnover ◽  
Bovine Heart ◽  
Diethyl Pyrocarbonate ◽  
Steady State Kinetic ◽  
State Kinetic

The histidine-specific reagent diethyl pyrocarbonate has been used to chemically modify bovine heart cytochrome oxidase. Thirty-two of sixty-seven histidine residues of cytochrome oxidase are accessible to modification by diethyl pyrocarbonate. Effects on the Soret and α bands of the heme spectrum indicate disturbance in the environment of one or both of the heme groups. However, diethyl pyrocarbonate modification does not alter the 830-nm absorbance band, suggesting that the environment of CuA is unchanged. Maximal modification of cytochrome oxidase by diethyl pyrocarbonate results in loss of 85–90% of the steay-state electron transfer activity, which can be reversed by hydroxylamine treatment. However, modification of the first 20 histidines does not alter either activity or the heme spectrum, but only when 32 residues have been modified are the activity and heme spectral changes complete. The steady-state kinetic profile of fully modified oxidase is monophasic; the phase corresponding to tight cytochrome c binding and low turnover is retained, whereas the high turnover phase is abolished. Proteoliposomes incorporated with modified oxidase have a 65% lower respiratory control ratio and 40% lower proton pumping stoichiometry than liposomes containing unmodified oxidase. These results are discussed in terms of a redox-linked proton pumping model for energy coupling via cytochrome oxidase.Key words: cytochrome oxidase, histidine modification, electron transfer, proton pumping, diethyl pyrocarbonate.

scholarly journals Steady-State Kinetic Analysis of Phosphotransacetylase from Methanosarcina thermophila

2006 ◽  
Vol 188 (3) ◽  
pp. 1155-1158 ◽  
Author(s):  
Sarah H. Lawrence ◽  
James G. Ferry
Keyword(s):  
Steady State ◽  
Kinetic Analysis ◽  
Random Order ◽  
Kinetic Mechanism ◽  
Methanosarcina Thermophila ◽  
Steady State Kinetic ◽  
Ping Pong ◽  
Acetyl Group ◽  
State Kinetic ◽  
Reversible Transfer

ABSTRACT Phosphotransacetylase (EC 2.3.1.8) catalyzes the reversible transfer of the acetyl group from acetyl phosphate to coenzyme A (CoA), forming acetyl-CoA and inorganic phosphate. A steady-state kinetic analysis of the phosphotransacetylase from Methanosarcina thermophila indicated that there is a ternary complex kinetic mechanism rather than a ping-pong kinetic mechanism. Additionally, inhibition patterns of products and a nonreactive substrate analog suggested that the substrates bind to the enzyme in a random order. Dynamic light scattering revealed that the enzyme is dimeric in solution.

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