The Kinetics of Succinyl Coenzyme A Synthetase from Escherichia coli
نویسندگان
چکیده
Succinyl coenzyme A synthetase from Escherichia coli does not exhibit a steady state kinetic pattern indicative of “ping-pong” kinetics, despite the fact that catalytic participation of a phosphorylated enzyme covalent intermediate has been established. Instead, kineti.c patterns are consistent with the sequential addition of all substrates, to form a quaternary complex, before the release of any product. Double reci.procal plots are intersecting with A.TP and succinate varied at nonsaturating concentration of the third substrate, CoA. These plots become parallel at hi.gher CoA concentrations, suggesting that CoA can be the second substrate to add in the binding sequence. Analogous reciprocal plots with ATP and CoA varied at both nonsaturating and saturati.ng succinate concentrations are also intersecting and parallel, respectively. The data may be reconciled with a binding sequence in which A.TP binds to the enzyme first, followed by the random addition of CoA and succinate. The finding of a sequential mechanism for the addition of substrates to this enzyme, whose catalysis is known to involve a covalent intermediate, serves to illustrate a possible danger in the use of initial rate kinetics. It is not possible to discount chemical mechanisms involving covalent intermediates by failure to observe the ping-pong kinetic pattern which may be anticipated for these catalytic routes.
منابع مشابه
The kinetics of succinyl coenzyme A synthetase from Escherichia coli. A reaction with a covalent enzyme-substrate intermediate not exhibiting "ping-pong" kinetics.
Succinyl coenzyme A synthetase from Escherichia coli does not exhibit a steady state kinetic pattern indicative of “ping-pong” kinetics, despite the fact that catalytic participation of a phosphorylated enzyme covalent intermediate has been established. Instead, kineti.c patterns are consistent with the sequential addition of all substrates, to form a quaternary complex, before the release of a...
متن کاملNovel mechanisms of Escherichia coli succinyl-coenzyme A synthetase regulation.
Low concentrations of ADP are shown to increase the rate of phosphoenzyme formation of E. coli succinyl-coenzyme A (CoA) synthetase (SCS) without altering the fraction of phosphorylated enzyme. This is true when either ATP or succinyl-CoA and Pi are used to phosphorylate the enzyme. The stimulatory effect of ADP is not altered by sample dilution, is retained upon partial purification of the enz...
متن کاملA phosphorus 31 nuclear magnetic resonance study of the intermediates of the Escherichia coli succinyl coenzyme A synthetase reaction. Evidence for substrate synergism and catalytic cooperativity.
متن کامل
The preparation, properties, and reactions of succinyl coenzyme A synthetase and its phosphorylated form.
A succinyl coenzyme A synthetase preparation from Escherichia coli has the following characteristics: apparent chromatographic, sedimentation, and electrophoretic homogeneity; molecular weight of about 141,000; Azso (1 mg per ml) = 0.511; higher specific activity than previous preparations; and identity by several criteria with a phosphorylated protein (E-P) obtained upon exposure to Mgf+, inor...
متن کاملSubunits of succinyl-coenzyme A synthetase: coordination of production in Escherichia coli and discovery of a factor that precludes refolding.
Succinyl-coenzyme A synthetase of Escherichia coli has an alpha 2 beta 2 subunit structure. By measuring reconstituted enzyme activity present after addition of purified alpha or beta subunits to cell extracts followed by refolding, we have shown that extracts contain no significant excess of either subunit species. This equivalence suggests that the expression of the respective structural gene...
متن کامل