Fatty acid esters of testosterone in rat brain: Identification, distribution, and some properties of enzymes which synthesize and hydrolyze the esters

Abstract

[4- 14C]Testosterone was converted to an unknown compound with a much higher R f on thin layer chromatogram than the substrate when it was incubated with a rat brain microsomal preparation. Evidence from its mass, infrared, and ultraviolet spectra indicated that the enzymic product is a mixture of fatty acid esters of testosterone. Saponification of the product yielded testosterone and a mixture of C 12:0, C 14:0, C 16:0, C 18:0, and C 18:1 fatty acids. The enzymic product was identical to testosterone laurate and testosterone stearate which were synthesized chemically. The enzyme system had a pH optimum at 4.9 with acetate buffer. The apparent K m was 8.3 × 10 −5 m for testosterone and 5.0 × 10 −5 m for palmityl CoA. An enzyme which hydrolyzes testosterone[1- 14C]oleate was also detected in rat brain. Most of this activity was in the nuclear and mitochondrial fractions. This enzyme had an optimum pH at 6.5 with phosphate buffer and its apparent K m was 2.1 × 10 −4 m. A low level of synthetic activity was found in fetal brain tissue which increased and reached a maximum at 3 weeks of age. The synthetic activity rapidly decreased with further increase in age. Hydrolytic activity was nearly undetectable in fetal rat brain, increased gradually until the animal reaches 3 weeks old, and remained at this level. Both synthetic and hydrolytic enzyme activities were higher in the brain than in other tissues examined.