CROSS-LINKED LDH CRYSTALS FOR LACTATE SYNTHESIS COUPLED TO ELECTROENZYMATIC REGENERATION OF NADH

Lactate dehydrogenase (LDH) was crystallized from concentrated ammoniu m sulfate solution and cross-linked with glutaraldehyde to afford long -lived enzymatically active cross-linked crystals (LDH-CLC). The cryst als were employed in an electrolytic cell for lactate production from pyruvate, in which the cathode consisted of a carbon electrode contain ing a coating of lipoamide dehydrogenase (LiDH) immobilized with methy l viologen under a Nafion membrane. This cell was more effective than a similar cell containing LDH in soluble form. An even greater improve ment in performance was achieved by chemically binding a viologen deri vative to the LiDH and using an electrode based on this modified enzym e in a cell containing LDH-CLC. The activity of the LDH-CLC is much le ss sensitive to pH than that of the soluble enzyme.