Phosphite dehydrogenase PTDH

In this particular case, we decided to take advantage of the favorable thermodynamic equilibrium constant that drives the oxidation of phosphite to phosphate mediated by a recently described phosphite dehydrogenase (PTDH) [117] to a nearly irreversible process [118]. The exquisite selectivity of PTDH for phosphite also precludes any side reaction that can occur in case, for example, an ADH is used. These characteristics render PTDH as an ideal candidate for use as a coenzyme regenerating enzyme (GRE) in combination with BVMOs or other NAD(P)H-dependent enzymes. 

This self-sufficient two-in-one redox biocatalyst enables the use of phosphite (HP03 ) as an inexpensive and sacrificial electron donor, and does not require an additional catalytic entity for coenzyme recycling. As model BVMOs, PAMO, CHMO, and CPMO were selected. No inhibition of the activity of either the BVMO or phosphite dehydrogenase (PTDH) by the substrate or product of the other subunit could be observed. 

Scheme 2.1 Practically irreversible oxidation of inorganic phosphite (hydrogen phospho-nate) to phosphate catalyzed by NADIPj -dependent phosphite dehydrogenase (PTDH).

Scheme 2.2 NADPH-dependent Baeyer-Villiger monooxygenases (BVMO) fused to a phosphite dehydrogenase (PTDH) for self-sufficient coenzyme regeneration.

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