Cytochrome P450 19 (CYP19, aromatase) catalyzes the conversion of androgens to estrogens in a sequence of three reactions that each depend on NADPH and O₂. Aromatase is a phylogenetically-ancient enzyme and its breadth of expression in other species has highlighted distinct physiological functions. In songbirds, estrogen production is required for programming the neural circuits controlling song and in the determination of sex in fish and reptiles. This work describes the expression, purification, and biophysical characterization of Aptenodytes forsteri (Emperor penguin) aromatase. Using human cytochrome P450 reductase as a redox partner, afCYP19 displayed similar substrate turnover and LC/MS/MS confirmed that afCYP19 catalyzes the transformations through the intermediates 19-hydroxy- and 19-oxo-androstenedione. Androstenedione and anastrozole had the highest affinity for the enzyme and were followed closely by 19-hydroxyandrostenedione and testosterone. The affinity of 19-oxo-androstenedione for afCYP19 was ten-fold lower. The time-dependent changes in the Soret bands observed in stopped-flow mixing experiments of the steroidal ligands and the inhibitor anastrozole with afCYP19 were best described by a two-step binding mechanism. In summary, these studies describe the first biophysical characterization of an avian aromatase that displays strikingly similar enzyme kinetics and ligand binding properties to the human enzyme and could serve as a convenient model system for studies of the enigmatic transformation of androgens to estrogens.

细胞色素P450 19（CYP19，芳香酶）以三个分别依赖于NADPH和O _2的反应顺序催化雄激素向雌激素的转化。芳香酶是一种系统发育的古老酶，它在其他物种中的表达广度突出了其独特的生理功能。在鸣禽中，为编程控制鸣叫的神经回路以及确定鱼类和爬行动物的性别而需要雌激素的产生。这项工作描述了Aptenodytes forsteri的表达，纯化和生物物理特性（帝企鹅）芳香酶。使用人细胞色素P450还原酶作为氧化还原伴侣，afCYP19显示出相似的底物周转率，LC / MS / MS证实afCYP19通过中间体19-羟基和19-氧代雄烯二酮催化转化。雄烯二酮和阿那曲唑对酶的亲和力最高，紧随其后的是19-羟基雄烯二酮和睾丸激素。19-氧-雄烯二酮对afCYP19的亲和力低十倍。在甾体配体和抑制剂阿那曲唑与afCYP19的停流混合实验中观察到的Soret谱带随时间的变化最好通过两步结合机制来描述。总之，