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The dependence of activities of Aspergillus phoenicis on the culture conditions in the progesterone transformation reaction was investigated. In the beginning of the reaction, 6,6, lla-dihydroxyprogesterone was not produced even at high concentration of lla-hydroxyprogesterone. However, large amount of the product was obtained after the complete exhaustion of progesterone. When spores of A. phoenicis replaced mycelia as enzyme source, lla-hydroxyprogesterone was produced after a considerably long induction period, and its maximum production rate followed the exponential growth phase. The 6,8-hydroxylation of l la-hydroxyprogesterone continued, even after the stationary growth phase. A. phoenicis showed high enzyme activity for these reactions when the phosphate buffer solutions were used in place of the ordinary culture medium. The buffer solutions of low pH gave more yield of 11 a-hydroxyprogesterone than those of high pH. However, the addition of glucose to the buffer solutions did not activate the transformation reaction. The presence of progesterone seems to be necessary for the induction of enzymes for the 6P-hydroxylation of l la-hydroxyprogesterone since 6,0, lla-dihydroxyprogesterone is not produced in the reaction medium containing only lla-hydroxyprogesterone as a substrate.
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