The effect of temperature and of cofactor concentrations on the conversion of 4-14C-progesterone to corticosterone by rat adrenal preparations

Abstract

When a Krebs–Ringer bicarbonate medium in which adrenal quarters have been preincubated (hereafter called PIM), is reincubated for 3 h in the presence of 4-14C-progesterone and a NADPH-generating system, it possesses the capacity of hydroxylating the progesterone molecule (5). When the PIM is prepared at 0 °C, its subsequent incubation at 37 °C enhances the conversion of progesterone to 21-hydroxy- and 11β-hydroxy-steroids 30-fold and fivefold, respectively, above those observed upon incubation of PIM prepared at 37 °C. Similarly when dilute homogenates (0.6 mg tissue per milliliter) are preincubated for 1 h at 21 °C prior to a 3-h incubation period in the presence of 4-14C-progesterone and proper cofactors, 21- and 11β-hydroxylations of progesterone are, respectively, six times and twice greater than when the preincubation temperature is 37 °C.It is concluded that: (i) 21- and 11β-hydroxylating systems are inactivated to a significant degree at 37 °C and that under these conditions the 21-hydroxylase system is much more labile than the 11β-hydroxylase system; and (ii) this difference in the degree of denaturation of these two steroid hydroxylase systems explains in part the accumulation of 11β-hydroxyprogesterone in the PIM as well as in homogenates.