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In this work, incubations of androstenedione 1 with Cladosporium sphaerospermum MRC 70266 and Ulocladium chartarum MRC 72584 have been reported. C. sphaerospermum MRC 70266 mainly hydroxylated 1 at C-6β, accompanied by a hydroxylation at C-15α, a reduction at C-17, a 5α-reduction and oxidations at C-6 and C-16 following hydroxylations. U. chartarum MRC 72584 hydroxylated 1 at C-6β, C-7α, C-7β and C-14α, accompanied by an oxidation at C-6 following its hydroxylation, a reduction at C-17 and a 5α-reduction. 6β,17β-Dihydroxyandrost-4-en-3,16-dione 8, one of the metabolites from the incubation of 1 with C. sphaerospermum MRC 70266, was determined as a new compound.

The utility of two locally isolated fungi, pathogenic to banana, for steroid biotransformation has been studied. The deuteromycetes Fusarium oxysporum var. cubense (IMI 326069, UAMH 9013) and Colletotrichum musae (IMI 374528, UAMH 8929) had not been examined previously for this potential. In general, F. oxysporum var. cubense effected 7α hydroxylation on 3β-hydroxy- Δ5-steroids, 6β, 12β, and 15α hydroxylation on steroidal-4-ene-3-ones, side-chain degradation on 17α,21-dihydroxypregnene-3,20-diones, and 15α hydroxylation on estrone. Both strains were shown to perform redox reactions on alcohols and ketones.

Cytochrome P450 2B1 wild-type and eight site-directed mutations at positions 114, 206, 236, 302, 363, 367, and 478 have been expressed in an Escherichia coli system. Solubilized membrane preparations yielded 100-180 nmol of P450/L of culture. The metabolism of a number of substrates including androstenedione, progesterone, (benzyloxy)resorufin, pentoxyresorufin, and benzphetamine was analyzed. The E. coli-expressed enzymes displayed the same androstenedione metabolite profiles previously observed with a COS cell expression system. Several of the mutants exhibited an increased rate of progesterone hydroxylation, possibly as the result of an enlarged substrate binding pocket and increased D-ring α-face binding. (Benzyloxy)resorufin and pentoxyresorufin O-dealkylation by the P450 2B1 mutants exhibited activities ranging from 10% to 99% and 3% to 71% of wild-type, respectively. Interestingly, the Val-363 → Leu mutant showed markedly suppressed pentoxyresorufin but unaltered (benzyloxy)resorufin dealkylase activity. Benzphetamine N-demethylase activities ranged from 28% to 110% of wildtype. Mechanism-based inactivation of the P450 2B1 mutants showed that susceptibility to inactivation by chloramphenicol and D-erythro- and L- threo-chloramphenicol was abolished in the Val-367 → Ala mutant. The Val- 363 → Leu mutant was refractory to L-threo-chloramphenicol. Studies of chloramphenicol covalent binding and metabolism by the Val-367 → Ala mutant showed that its resistance to inactivation is largely attributable to an inability to bioactivate the inhibitor. The expression of P450 2B1 wild-type and mutants in E. coli provides an excellent opportunity to study structure/function relationships by site-directed mutagenesis.