The Inhibitory Effect of Cyclodextrin on Oxygen Bioavailability Is a Key Factor for the Metabolic Flux Redistribution Toward Steroid Alcohols in Phytosterol Resting Cells Bioconversion

In the present work, we tried to identify mechanism why by which steroid alcohols accumulated when hydroxypropyl-β-cyclodextrin (HP-β-CD) was enhance sterol conversion rate. Compared with bioconversion system without HP-β-CD, reaction rate greatly improved in presence of but largely concurrently. a an enhanced rate, higher intracellular NADH/NAD+ level detected, and production increased also. Mycobacterium neoaurum mutants KshA activity (3-ketosteroid 9α-hydrolase, monooxygenase hydroxylating nucleus at C-9 expense NAD(P)H consumption) reduced alcohol production, meantime, decreased consequently. Further research found that oxygen availability seriously inhibited cyclodextrin system. These results indicated NADH formed not properly regenerated via respiratory chain because poor bioavailability. The inhibitory effect on bioavailability is key factor for metabolic flux redistribution toward phytosterol resting cells bioconversion.