Hadjiconstantinou M, Rossetti Z, Silvia C, Krajnc D, Neff N H
Department of Pharmacology, Ohio State University College of Medicine, Columbus 43210-1239.
J Neurochem. 1988 Nov;51(5):1560-4. doi: 10.1111/j.1471-4159.1988.tb01125.x.
Aromatic L-amino acid decarboxylase (AAAD) activity of rat retina is low in animals placed in the dark. When the room lights are turned on, activity rises for almost 3 h and reaches values that are about twice the values found in the dark. A study of the kinetics of the enzyme revealed that the apparent Km values for L-3,4-dihydroxyphenylalanine and pyridoxal-5'-phosphate were unchanged in light- and dark-exposed animals, whereas the Vmax increased in the light. Treating the animals with cycloheximide before exposure to light prevented the increase of enzyme activity. Immunotitration with antibodies to AAAD suggested that more enzyme molecules are present in the light than in the dark. When the room lights are turned off AAAD activity drops rapidly at first and then more slowly, suggesting that at least two processes are responsible for the fall of enzyme activity. Exposure to short periods of dark followed by light results in a rapid increase of AAAD activity. Mixing homogenates from light- and dark-exposed rats results in activity values that are less than expected, suggesting the presence of an endogenous inhibitor(s). These studies demonstrate that AAAD activity is modulated in vivo.
在置于黑暗环境中的动物体内，大鼠视网膜的芳香族L-氨基酸脱羧酶（AAAD）活性较低。当房间灯光打开时，该活性会升高近3小时，并达到约为黑暗环境中所测值两倍的值。对该酶动力学的研究表明，暴露于光照和黑暗环境中的动物，其L-3,4-二羟基苯丙氨酸和磷酸吡哆醛的表观Km值未发生变化，而Vmax在光照下增加。在光照前用环己酰亚胺处理动物可阻止酶活性的增加。用抗AAAD抗体进行免疫滴定表明，光照下存在的酶分子比黑暗中更多。当房间灯光关闭时，AAAD活性起初迅速下降，然后下降速度变慢，这表明至少有两个过程导致酶活性下降。短时间暴露于黑暗后再进行光照会导致AAAD活性迅速增加。将光照和黑暗暴露大鼠的匀浆混合后，活性值低于预期，这表明存在内源性抑制剂。这些研究表明，AAAD活性在体内受到调节。
