Inhibitory Effect of Polyelectrolytes on Oligomeric Enzymes

E. A. Saburova^1*, M. E. Bobreshova², L. I. Elphimova³, and B. I. Sukhorukov¹

¹Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; E-mail: saburova@mail.ru

²Moscow State Academy of Instrument Making and Informatics, Pushchino, Moscow Region, 142292 Russia

³Institute of Cell Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia

^* To whom correspondence should be addressed.

Received November 24, 1999; Revision received January 18, 2000

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The effect of polyelectrolytes on the stability and catalytic characteristics of oligomeric enzymes--pig muscle lactate dehydrogenase (LDH) and bovine liver glutamate dehydrogenase (GDH)--was studied by fluorescent spectroscopic and steady state kinetic methods. It was shown that the binding of negatively charged polyelectrolytes--polystyrene sulfonate, polymethacrylate, and polyphosphate--destroys the tertiary and partially the secondary structure of LDH and GDH, resulting in their complete inactivation at pH < 7. The concentrations of polyelectrolytes needed for inhibition of the enzymes were in this case by two or more orders of magnitude lower than the corresponding concentrations for monomers--toluene sulfonate, methacrylate, and phosphate. The affinity of the substrate (pyruvate) for LDH did not vary in the presence of the polyelectrolytes, but the inhibition was removed by excess of substrate. We propose that the oligomeric state of enzymes causes polyelectrolytes to act on them in a special manner, this special effect differing significantly from the effect of polyelectrolytes on monomeric enzymes. The effect consists in that polyelectrolytes cleave the oligomeric structure of the enzymes, this “cleaving” effect being higher the greater the hydrophobicity of the polyelectrolyte chain.

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KEY WORDS: polyelectrolytes, inhibitors, oligomeric enzymes, lactate dehydrogenase, glutamate dehydrogenase, stability, polystyrene sulfonate, polymethacrylic acid, polyphosphate

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