Editors note. Some problems remain with the reactions schemes in this poster.
UV - HYDROLYSIS OF PHOSPHOENOLPYRUVATE AS A MODEL OF PEP-DEPENDENT ENZYMATIC CATALYSIS
Alexander Yasnikov, Natalia Samus.
Institute of bioorganic chemistry and petrochemistry, National Academy of Sciences of Ukraine,
Murmanskaya, 1, 253660, Kiev, UKRAINE, E-mail: users @ bpci. kiev. ua
In the present work hypothesis about the nature of excited intermediate states of PEP enzymatic reactions is proposed. It is known that the first step of these reactions is PEP decay to enolpyruvate (EP) and PO3- ion, but the mechanism of such decay remained unknown. In the model reactions of PEP hydrolysis in J2 presence it was established that the decay is conditioned by formation of charge-transfer complex PEP--J+. At UV-lighting (220-250 nm) of PEP water solutions a hydrolysis proceeds. Olefins exciting leads to formation of oscillatory-excited biradical triplet state. In the case of PEP one- electron transfer from oxygen atom, which binds phosphoryl group, to carbon atom with cation-radical formation may be suggested. At 20oC the decay of photoexcited state proceeds via solvolysis mechanism under the strong base participation. Unlike this at 50oC photoexcited state reversibly dissociates to EP and PO3-. In accordance to PEP-carboxylase model, HCO3- ion shows the catalytic action. In this reactions AMP, H2PO4- and H2P2O72- ions are phosphorylated.
Enzymatic PEP hydrolysis by acid phosphatase (AP) from wheat germs proceeds with two enzyme molecules participation. At the same time ATP, ADP and p-nitrophenylphosphate (NPP) are hydrolysed on the each subunit of AP. After the comparison of enzymatic and biomimetic catalysis such mechanism was considered: PEP double bond is activated by the formation of complex with AP proton-donor group and than transfer of PEP phosphoryl residue onto the imidasol group of the enzyme occurs. It is shown that PEP hydrolysis in phosphatase reaction proceeds with zero activation energy (Ea). At the same time NPP has a high Ea. The hypothesis about the transference of PEP energy onto the intermediate product of phosphatase reaction is proposed.