Screening of whole-cell immobilization procedures for the delta 1-dehydrogenation of steroids in organic medium.

Different whole-cell immobilization methods and conditions were tested for the delta 1-dehydrogenation of 6-alpha-methyl-hydrocortisone-21-acetate with Arthrobacter simplex cells, in n-decane-1-ol and chloroform. Among the entrapment methods, polyurethane foams gave the best productivity of n-decane-1-ol, but could not be used in chloroform. Partition and diffusional barriers appeared to be the factors limiting productivity in entrapped-cell systems. The coentrapment of enzyme-stabilizing (glycerol, sucrose, sodium sulfate, monosodium glutamate) or hydrophobic additives did not significantly improve dehydrogenation rates in chloroform, although in some cases higher activities resulted in n-decane-1-ol. Dehydration of kappa-carrageenan-immobilized cells lowered the productivity in both solvents. The use of cell adsorption methods on silica-based carriers produced biocatalysts that in some cases were more active in chloroform than the entrapped cells. However, the surface-attached cells appeared to be more sensitive to solvent toxicity, more hydrophilic supports generally giving higher dehydrogenation rates. The estimated partition coefficients for the substrate between several of the tested supports and the two solvents are also presented. High partition ratios followed high measured activities in entrapment matrices but not in Celite (cell adsorption matrix). Activities in chloroform were always very low (less than 1 mumol product per hour and gram of cell dry weight). Polyurethane entrapment with n-decane-1-ol as a reaction medium was the most promising system, with measured dehydrogenation rates up to 40 times higher.