Interaction of electrically charged lipid monolayers with malate dehydrogenase.

Malate dehydrogenase was adsorbed onto monomolecular lipid films, using a multicompartment trough. The quantity of adsorbed protein and its enzymatic activity were studied with monolayers of various electrical charge densities and subphases of various electrolyte compositions. A closely packed layer of enzyme molecules was adsorbed onto negatively charged films, whereas considerably less protein was adsorbed onto neutral and positively charged monolayers. Electrolytes reduce the quantity of adsorbed protein. The adsorption was found to be irreversible even at high ionic strength. When adsorbed to uncharged lipid films the enzyme is nearly inactive, whereas negatively charged lipid headgroups enhance the specific activity of the enzyme.