A cell suspension in a water‐insoluble organic solvent (benzene: n‐heptane, 1 : 1 by volume) of Nocardia rhodocrous (previously induced to synthesize steroid Δ1dehydrogenase) rapidly catalyzed the stoichiometric oxidation of 4‐androstene‐3,17‐dione (4‐AD) to androst‐l,4‐diene‐3,17‐dione (ADD) in the presence of phenazine methosulfate (PMS). High levels of 4‐AD or PMS reduced the conversion rates. No appreciable decrease in the conversion rate was observed on adding aqueous buffer solution to the thawed ceils (up to 9.4 g water/g dry cell). The whole cells were immobilized by entrapment in a hydrophilic gel (H‐gel) or a lipophilic gel (L‐gel) by use of a water‐soluble or water‐insoluble photocrosslinkable prepolymer. The reticula of H‐ and L‐gel matrices were impregnated with water and organic solvent, respectively. Both the H‐ and L‐gels could convert 4‐AD to ADD in the presence of PMS, the L‐gel showing a slightly higher conversion rate. Various lines of evidence indicate that the limiting factor is the penetration rate of 4‐AD into gel particles for the H‐gel, and the penetration rate of PMS for the L‐gel. The catalytic activities decreased considerably after several successive runs with the free cell suspension system, while the immobilized cells were more stable, the stability of H‐gel and L‐gel being almost the same. Copyright © 1979 John Wiley & Sons, Inc.
