Inhibitory effect of polyelectrolytes on oligomeric enzymes

The effect of polyelectrolytes on the stability and catalytic characteristi cs of oligomeric enzymes-pig muscle lactate dehydrogenase (LDH) and bovine liver glutamate dehydrogenase (GDH)-was studied by fluorescent spectroscopi c and steady state kinetic methods. ft was shown that the binding of negati vely charged polyelectrolytes-polystyrene sulfonate, polymethacrylate, and polyphosphate-destroys the tertiary and partially the secondary structure o f LDH and GDH, resulting in their complete inactivation at pH < 7. The conc entrations 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 prese nce of the polyelectrolytes, but the inhibition was removed by excess of su bstrate. We propose that the oligomeric state of enzymes causes polyelectro lytes to act on them in a special manner, this special effect differing sig nificantly from the effect of polyelectrolytes on monomeric enzymes. The ef fect consists in that polyelectrolytes cleave the oligomeric structure of t he enzymes, this "cleaving" effect being higher the greater the hydrophobic ity of the polyelectrolyte chain.