|
In a non-aqueous medium, ATP formation was observed from ADP and inorganic phosphate anion by coupling with the reaction between p- benzoquinone and imidazole. The purpose of this study is to investigate the essential mechanism of phosphorytation reaction. Furthermore, in order to clarity the reaction, efforts were also made to find out the optimum analytical conditions for the separation and quantitization of AMP, ADP and ATP during the reaction process.
First of all, in the reaction system, p-benzoquinone and imidazole were found to produce an addition compound, 2-imidazoly1 hydroquin-one. This compound was then oxidized readily by aerobic oxygen or by unreacted p-benzoquinone, and produced 2-imidazoly1 semiquinone anion radicals in DMAC. Naturally p-benzosemiquinone anion radical was also present in the latter case. However in other less polar, less basic non-aqueous solvents, such as THF and acetonitrile, insoluble quinhydrone-type product between the two rather than two kinds anion radicals was observed when excess p-benzoquinone was present in the system.
2-Imidazoly1 semibenzoquinone anion radical which absorbed at 468nm was found as a strong one-electron reducing agent, capable of reducing the adenine ring of ADP, which in turn, could increase the basicity of the amino group in the ring to such an extent that the inorg- anic phosphate was attracted by the group. This phosphate group could be transferred to the terminal pyrophosphate group of ADP during a dehydration process and produced ATP.
Theoretical consideration as well as kinetic studies by comparing AMP- and ADP-containing system in the phosphorylation reaction has strongly suggested that, ADP in a natural condition has a folded confor- mational arrangement which makes ADP to be a better phosphate-accept- or than AMP.
|