Cross-Linked LDH Crystals for Lactate Synthesis Coupled to Electroenzymatic Regeneration of NADH

Lactate dehydrogenase (LDH) was crystallized from concentrated ammonium sulfate solution and cross-linked with glutaraldehyde to afford long-lived enzymatically active cross-linked crystals (LDH-CLC). The crystals were employed in an electrolytic cell for lactate production from pyruvate, in which the cathode consisted of a carbon electrode containing a coating of lipoamide dehydrogenase (LiDH) immobilized with methyl viologen under a Nafion membrane. This cell was more effective than a similar cell containing LDH in soluble form. An even greater improvement in performance was achieved by chemically binding a viologen derivative to the LiDH and using an electrode based on this modified enzyme in a cell containing LDH-CLC. The activity of the LDH-CLC is much less sensitive to pH than that of the soluble enzyme.