Side-chain cleavage of cholesterol to C 6 and C 8compounds by adrenal and testis tissue preparations

Abstract

1. 1. Using gas-liquid chromatography the conversion of [25,26- 3H 2]cholesterol to isocaproaldehyde, isohexanol, isocaproic acid, 2- methylheptan-6- one and 2- methylheptan-6- ol has been studied with adrenal and testis preparations without the addition of “trapping” agents. 2. 2. With bovine adrenocortical mitochondrial soluble preparations, isocaproaldehyde, isohexanol and isocaproic acid were formed. In some of the bovine, preparations either isocaproaldehyde or isohexanol predominated, but in none was the isocaproic acid a major product. 3. 3. With human and chicken adrenal acetone-dried powders isohexanol was observed as the major product along with smaller amounts of isocaproaldehyde and isocaproic acid. 4. 4. [4,5- 3H 2] Isocaproaldehyde, of the same specific activity as the [25,26- 3H 2]-cholesterol used, was rapidly converted to isohexanol and isocaproic acid with a bovine acetone-dried powder preparation and to isohexanol with a human adrenal preparation, strongly indicating that isocaproaldehyde was the primary product of the cholesterol side-chain cleavage. These studies appear to be the first demonstration of the existence of an isocaproaldehyde reductase system in adrenal preparations. 5. 5. With a soluble bovine acetone-dried preparation in which cholesterol was converted predominantly to isocaproaldehyde and in which pregnenolone was not significantly further converted to other products, a 1:1 stoichiometric relationship was observed between this C 21 steroid and the sum of the C 6 compounds formed. A similar 1:1 stoichiometry was also observed with two human adrenal acetone-dried powders, in which the further metabolism of pregnenolone was insignificant. 6. 6. No 2-methylheptan-6-one or 2-methylheptan-6-ol was formed with a human adrenal mitochondrial acetone-dried powder preparation obtained from a patient with an androgen-secreting adrenal carcinoma. 7. 7. Incubation of rat testis and adrenal homogenates with [25,26- 3H 2]cholesterol after the procedure of Jungmann ( Biochim. Biophys. Acta, 164 (1968) 110) yielded isocaproic acid as the only positively identifiable volatile product. The carrier C 8 compounds 2- methylheptan-6- ol and 2-methylheptan-6-one added at the end of the incubation were isolated either devoid of radioactivity or containing insignificant counts as compared to the isocaproic acid. The mean maximal possible combined radioactivity in these two C 8 compounds was 1 500 and 1 4000 of that found in the isocaproic acid obtained with testis and adrenal homogenates, respectively. This contrasted with the studies by Jungmann 7 who reported ratios of 1 2.4 and 1 15.4 for 2- methylheptan-6- one, with these two tissues, respectively.