Immobilization of Arthrobacter simplex in thermally reversible hydrogels: effect of gel hydrophobicity on steroid conversion

Abstract

Arthrobacter simplex cells have been immobilized in a series of thermally reversible hydrogels having different gel hydrophobicities. Steroid conversion from hydrocortisone to prednisolone via the delta 1-dehydrogenase system was greatly affected by the relative hydrophobicities of the gel matrices, which were prepared by copolymerizing varying ratios of N-isopropylacrylamide to acrylamide. The characteristics of the immobilized cells, such as optimal temperatures, Km values, and the effects of an added artificial electron acceptor, were largely influenced by the gel matrices and their different lower critical solution temperatures (LCST). The data indicate that the microenvironment of the dehydrogenation system is quite different within the different hydrophilic/hydrophobic gel matrices. The high partitioning of water-insoluble steroids into the hydrophobic regions and the reduced possibility of product inhibition within the more hydrophobic gel matrices may cause the observed higher steroid conversion in these gels. A possible model for immobilized A. simplex cells in such different gel matrices is proposed.