Phosphoenolpyruvate carboxylase

The enzyme phosphoenolpyruvate carboxylase ( PEPC1 ) irreversible carboxylation of phosphoenolpyruvate to oxaloacetate in plants and bacteria. It is an important switch point in the plant metabolism, and therefore they can be used in plants as a biomarker. Various harmful images ( plant diseases with causally related to lack of supply) measured with reasonable accuracy and the assessment of forest damage can be improved compared to the exclusive observation of indicator plants.

Introduction

PEP carboxylase is a key enzyme of bacteria and plants, in particular for the reductive carbon dioxide fixation in C4 plants. In addition, it is an alternative to quantitatively most common enzyme on earth at all, the ribulose bisphosphate carboxylase ( RubisCO ), which plays a central role in the reductive carbon fixation of C3 plants. The enzyme is structurally a tetramer with approximately equal size blocks. It is under the symbols PEPC, Pepca and Pepca -A as well, starting from the underlying genotype, known also other shortcuts analogue construction. The structure of the enzyme ( to Marion O'Leary ) is not uniform, but reflects the low, genetic variations. Interesting are the variations of PEPC in different organisms. For example, in Methanothermobacter thermautotrophicus, where the individual tetramers are only 55 kDa heavy, which corresponds to about half of the otherwise encountered variants. The importance of PEPC is also reflected in your distribution. Even Methanopyrus kandleri has its own ( also very startling ) PEPC and usually lives in the hot water puddles of volcanoes, which is unusual considering the temperature dependence of PEPC.

Data

• PEPC is a lyase, which is functionally specifies a CC lyase or a carboxy - lyase.
• Tetramer structure ( four large proteins are the basic modules, which assemble into a giant molecule )
• 100-130 kDa per subunit
• Michaelis constant for the primary reaction of PEP ( phosphoenolpyruvate ) to oxaloacetate at 5-6 x 10-4 mol / l for PEP and 3.1 x 10-3 mol / L for HCO3-
• In the balance sheet strong exothermic reaction, therefore, quasi- irreversible, ie not to provide equilibrium constant sense

Benefit

Based on the genetic differences there are slight variations within botanically identical representatives of the same species, which is reflected in addition to structural differences in the measurable enzymatic activity and specific tolerances of trees and other plants to environmental toxins. These differences are, at sufficiently accurate measurement methods, highly reliable measures of the health of the plant.

PEPC is a molecular marker to weeks - month period in responding to harmful influences from the environment. Significantly, the enzyme responds to a (increased, and with slightly reduced accuracy even humiliated ) nitrogen supply and to the phosphate regulation; furthermore, one can show that PEPC responsive to ozone, the magnesium supply and heavy metals and pesticides. The response is well quantified, by making use of appropriate clones to be examined as a reference plant. Even with artificial Essays ( model compounds ) can achieve sufficient accuracy for practical damage assessment.

Metabolic role of PEPC

• In C4 plants: CO2 fixation by PEPC to C4 acids, malate and aspartate
• In C3 plants: CO2 fixation by RubisCO to 3 -phosphoglycerate anaplerotic role of PEPC in the citric acid cycle; indirectly the PEPC is directly coupled to nitrate assimilation via the citric acid cycle, resulting in the role as a biomarker for nitrogen load can be justified. PEPC is involved in the NADPH synthesis.

Reaction

Balance

PEP reacts with CO2 ( as HCO3- ) using Mg2 as a catalyst in the reaction center of PEPC to oxaloacetate.

In model solution can describe the equilibrium underlying this:

In general, other divalent metal ions are also possible. The reaction proceeds according to O'Leary as irreversible beta- carboxylation of PEP.

Mechanism

In principle, the reactants are transported into the reactive site of the enzyme, which is located approximately centrally in the tetramer. Where the PEP is relatively centrally located, the Mg2 is taken as a catalyst in the vicinity of the reaction center and then moves the hydrogen in the vicinity of the reaction site. The molecular pocket to the reaction center around is well suited for this purpose because it is not only protected from contamination by a relatively long path of the starting materials and because they generate on the other next to a favorable steric arrangement of the Reaktanen a very favorable energetic environment. It is discussed whether possibly even the energetic control of the reaction is influenced by the enzyme. After the reaction, the products are discharged again, which is probably favored or initiated by the enzyme.