Book of Abstracts: Albany 2009
June 16-20 2009
© Adenine Press (2008)
The Binding of Citrate Synthase and Malate Dehydrogenase with the Inner Mitochondrial Membrane
In the last twenty years it has been demonstrated that sequential enzymes which operate within metabolic pathway interact with each other to form highly organized complexes. The term ?metabolon? was introduced by Paul Srere to describe such enzyme-enzyme complexes (1). In a series of previous studies with use of various methodological approaches it has been shown that interaction occur between two sequential enzymes of Tricarboxylic acid cycle ? mitochondrial citrate synthase and mitochondrial malate dehydrogenase (mMDH) (2-4) but no interaction between citrate synthase and cytosolic malate dehydrogenase (cMDH).
Channeling of oxaloacetate in the malate dehydrogenase and citrate synthase-coupled systems was tested using polyethylene glycol precipitates of CS and mMDH, and citrate synthase and cMDH. The effectiveness of large amounts of aspartate aminotransferase and oxaloacetate decarboxylase, as competing enzymes for the intermediate oxaloacetate, was examined. Aspartate aminotransferase and oxaloacetate decarboxylase were less effective competitors for oxaloacetate when precipitated citrate synthase and mMDH in polyethylene glycol was used at low ionic strength compared with free enzymes in the absence of polyethylene glycol or with a co-precipitate of citrate synthase and cMDH. Substrate channeling of oxaloacetate with citrate synthase-mMDH precipitate was inefficient at high ionic strength. These effects could be explained through electrostatic interactions of mMDH but not cMDH with citrate synthase.
Also, the specific binding of the enzymes studied to the inner surface of the mitochondrial inner membrane was demonstrated by absorbtion experiments (Table) and using immunochemical method with gold colloids labelling antibodies (Figure ).
Figure: The schematic image of procedure of labelling of CS and mMDH by colloid gold.
References and Footnotes
Igor G. Morgunov*
G. K. Skryabin Institute of Biochemistry and Physiology of Microorganisms