EFFECT OF MALEATE COUNTERION ON MALEASE ACTIVITY - PRODUCTION OF D-MALATE IN A CRYSTAL LIQUID 2-PHASE SYSTEM

Malease activity of permeabilized cells of Pseudomonas pseudoalcaligen es was strongly affected by the maleate salt used as the substrate. Wi th Na-2-maleate as the substrate, malease activity decreased strongly with increasing substrate concentrations. By using counterions other t han sodium, the concentration of available dissociated maleate, the '' real'' substrate for the enzyme, could be reduced significantly, owing to metal-substrate complex formation. Use of metal ions that resulted in the formation of an insoluble metal-substrate complex, such as Ca2 + and Ba2+, further reduced the malente(2-) concentration. The use of these metal ions resulted in the formation of a crystal-liquid two-pha se system, owing to the low solubility of both the metal-substrate and the metal-product complex. Ca2+ was found to be the best counterion f or the conversion of high concentrations (up to 160 gl(-1)) of either maleate or citraconate by malease into D-malate and D-citramalate, res pectively, with yields >99%. The use of this metal ion gave the highes t malease activities and no substrate inhibition could be observed usi ng this counterion.