Primary Study On The 11α-hydroxylation Of Steroids And Its Kinetics Of Rhizopus Nigricans

Steroid hormone medicines such as dexamethasone are an important style of clinical practical medicines, which are widely applied in the clinical therapy. They play an important role in the fields of anti-infectious inflammation, anti-non-infectious inflammation, anti-allergic, antiendotoxin, immunosuppression and so on. 11α-epoxyprogesterone is an important intermediate in the process of making dexamethasone, whose yielding rate affected seriously the productive cost of dexamethasone.Due to the hard solubility of substrate epoxyprogesterone in the water, the effect of organic solvents dissolution, surface active medical Tween 80 dispersion, substrate refinement on the bioconversion rate and its dissolution was studied. The final optimal substrate suspension composition was achieved: 1.5% Tween 80 was added in the 8 mL substrate suspension with 1.2 mL acetone and 1 g substarte. Besides enhancing the solubility of the substrate, acetone could improve the catalysis of the P450 enzymes of rhizopus nigricans and its bioconversion rate.In our study, the hydroxylation of epoxyprogesterone by rhizopus nigricans was studied under the conditions of different time of adding substrate to the fermentation, pH, etc. The uniform design was used to obtain optimal culture medium ingredients. Then based on the optimal fermentation conditions and suitable batch substrate adding method, the hydroxylation of rhizopus nigricans was studied in the 1L fermentor. The bioconversion rate reached 57.8 % in 70h, with the final substrate concentration of 1.75 g/L.Finally, under the conditions of the glucose as carbon source and energy source, the improved Contois equation was employed to describe the cell growth kinetics. Its cell growth yield was obtained using the following equation: C_{X ,max}= Y_XSC_S⁰ + C_X⁰. The bioconversion process kinetic equation was obtained by using pseudo steady state approximation according the hydroxylation principle.