The effect of freeze-drying on the quaternary structure of L-asparaginase from Erwinia carotovora.

ABSTRACT

L-Asparaginase (L-asparagine amidohydrolase, EC 3.5.1.1) from Erwinia carotovora undergoes extensive dissociation from active tetramer to inactive monomers when freeze-dried. The monomeric state is stabilized by reconstitution of the freeze-dried enzyme with buffers of high pH and high ionic strength. Some compounds, particularly sugars and sugar derivatives, prevent dissociation on freeze-drying, whereas others, such as urea and chaotropic ions, increase dissociation. The effects of additives are not related to water retention. The dissociation is completely reversible on reconstitution at neutral pH, but the alkali-stabilized monomer only partially reassociates when the pH is brought back to neutrality.