| Description |
It has been shown by in vitro incubations that cell-free homogenates of testicular tissue from the English sparrow (Passer domesticus) are capable of synthesizing androgenic steroid hormones for 4-pregnen-3,20-dione-4-C14 by a pathway involving 17?-hydroxylation, cleavage of carbons 20 and 21 to form 4-androstein-2, 17-dione, and reduction of the 17-ketone to form 4-androsten-17?-ol-3-one. The only exogenous cofactor required for this sequence of reactions in reduced triphosphopyridinenucleotide. In addition, both 4-pregnen-3, 20-dione, and 4-pregnen-17?-ol-3, 20-dione are reduced at the 20-ketone to form 4-pregnen-20?-ol-3-one, 4-pregnen-20?-ol-3-one, 4-Pregnen-17?, 20?-diol-3-one, and 4-pregnen-17?, 20?-diol-3-one. Two other products of progesterone metabolism believed to be 4-pregnen-20?-ol-3-one and 4-pregnen-20?-ol-3-one with a second hydroxyl at a position in the steroid nucleus have been incompletely identified. The variation of the testicular content of the 17?-hydroxylase and the two progesterone-20-ketone reductases over a wide range of natural and artificial testicular stimulation was determined. It was found that on a milligram of protein basis the 17?-hydroxylase decreased by a factor of 10 with an increase in testis weight from 7.2 to 480 milligrams, whereas the 20-ketone reductases remained relatively constant or decreased to a musch lesser extent, by a factor of two, over similar testicular weight changes. Calculated on the basis of enzyme content per bird by use of an average combined testicular weight, the total testicular 17?-hydroxylase increased by a factor of three to four, while the 20-ketone reductases increased by a factor of twenty to forty when the mean testicular weight increased from 7.2 to ca. 500 milligrams. Artificial testicular simulation with human chorionic gonadotropin stimulation both the 17?-hydroxylase and 20-ketone reductases, but appeared to have greater effect on the 17?-hydroxylase. |
