Studies on the catalytic function of aromatase: aromatization of 6-alkoxy-substituted androgens.
To gain insight into the catalytic function of aromatase, we studied aromatization of a series of 6alpha- and 6beta-ether-substituted (methoxy, ethoxy, and n-butoxy) androst-4-ene-3,17-dione (AD) steroids (1 and 2) and their androsta-1,4-diene-3,17-dione (ADD) derivatives (3 and 4) with human placental aromatase by gas chromatography-mass spectrometry (GC-MS). Among the steroids examined, 6beta-methoxy and 6beta-ethoxyADDs (4a and 4b) are suicide substrates of aromatase. All of the steroids were found to be converted into the corresponding 6-alkoxy estrogens. Introduction of the alkoxy groups at C-6 of AD or ADD decreased the ability of these to serve as a substrate of aromatase. In 6alpha-alkoxy steroid series, compounds 1 and 3, the aromatization rate increased by elongating the 6-methoxy group up to the n-butoxy group whereas, in the 6beta-isomers series, 2 and 4, the rate decreased due to this structural modification. 6beta-Alkoxy steroids, 2 and 4, including the suicide substrates, were extremely poor substrates for the aromatization reaction. Apparent K(m) values obtained for 6alpha-alkoxy compounds 1 and 3 were similar to each other, ranging from 92 to 111nM, as shown by their previously-obtained K(i) values. The findings indicate that the stereochemistry as well as the bulkiness of the 6-ether-substituent play an important role in the ability to serve as a substrate. It is also predicted that the aromatization reaction and the mechanism-based inactivation reaction would be related and have a definite partition number which is characteristic to the compound in a series of suicide substrates.
Numazawa
Mitsuteru
M
Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aobaku, Sendai 981-8558, Japan. numazawa@tohoku-pharm.ac.jp
Ando
Momoko
M
Zennyoji
Rika
R
D000735:Androstenedione / Q000378:metabolism*; D001141:Aromatase / Q000302:isolation & purification / Q000502:physiology*; D002384:Catalysis; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology / Q000378:metabolism; D015394:Molecular Structure; D010920:Placenta / Q000201:enzymology; D011247:Pregnancy; D013329:Structure-Activity Relationship
D004791:Enzyme Inhibitors; D000735:Androstenedione; D001141:Aromatase