Rossetti Z, Krajnc D, Neff N H, Hadjiconstantinou M
Department of Pharmacology, Ohio State University College of Medicine, Columbus 43210-1239.
J Neurochem. 1989 Feb;52(2):647-52. doi: 10.1111/j.1471-4159.1989.tb09169.x.
Aromatic L-amino acid decarboxylase (AAAD) activity of the rat retina increases when animals are placed in a lighted environment from the dark. The rise of activity can be inhibited by administering alpha 2 adrenoceptor agonists. In the dark, the enzyme activity can be made to increase by administering alpha 2 adrenoceptor antagonist drugs. Kinetic analysis indicates that the maximum velocity of the enzyme increases with little change of the Km for the substrate L-3,4-dihydroxyphenylalanine or the cofactor pyridoxal-5'-phosphate. The rise of activity in the light and in the dark after alpha 2 antagonists can be blocked by administering cycloheximide, suggesting that protein synthesis is needed for the response. We speculate that epinephrine released in the dark from a subpopulation of retinal amacrine cells onto alpha 2 receptors suppresses AAAD activity that is associated with dopaminergic amacrines.
当动物从黑暗环境转移到光照环境中时，大鼠视网膜的芳香族L-氨基酸脱羧酶（AAAD）活性会增加。给予α2肾上腺素能受体激动剂可抑制活性的升高。在黑暗中，给予α2肾上腺素能受体拮抗剂药物可使酶活性增加。动力学分析表明，该酶的最大反应速度增加，而底物L-3,4-二羟基苯丙氨酸或辅因子磷酸吡哆醛的米氏常数变化不大。给予环己酰亚胺可阻断α2拮抗剂作用后在光照和黑暗条件下的活性升高，这表明该反应需要蛋白质合成。我们推测，在黑暗中，视网膜无长突细胞亚群释放的肾上腺素作用于α2受体，抑制了与多巴胺能无长突细胞相关的AAAD活性。
