Whole-cell bioreduction of aromatic α-keto esters using Candida tenuis xylose reductase and Candida boidinii formate dehydrogenase co-expressed in Escherichia coli

Table 4 Effect of varied activity ratio for Ct XR and Cb FDH during whole cell-catalyzed reduction of 100 mM ethyl 4-cyanobenzoylformate by a suitable mixture of E. coli XR_FDH and E. coli FDH.

substrate conc. [mM]	XR : FDH	additive^1,2	yield [mM]³/ee [%]⁴
100	1 : 2	polymyxin B	18/86.1 R
100	1 : 6	polymyxin B	36/74.6 R
100	1 : 20	polymyxin B	62/71.3 R
100	1 : 2	NAD⁺, polymyxin B	23/66.8 R
100	1 : 6	NAD⁺, polymyxin B	36/64.7 R
100	1 : 20	NAD⁺, polymyxin B	64/71.2 R
500	1 : 2	polymyxin B	25/≥ 99.9 R
500	1 : 6	polymyxin B	39/84.6 R
500	1 : 20	polymyxin B	88/73.7 R
500	1 : 2	NAD⁺, polymyxin B	29/≥ 99.9 R
500	1 : 6	NAD⁺, polymyxin B	42/85.1 R
500	1 : 20	NAD⁺, polymyxin B	90/75.5 R

The activity of Ct XR was kept constant at 1.4 U/mL throughout.
¹ [NAD⁺] = 490 μM, ² [polymyxin B sulphate] = 144 μM;³Standard errors ≤ 15%. ⁴Detection limit of ethyl 4-cyanomandelate is below 0.01 mM.

ISSN: 1475-2859