Mechanism of inhibition of aldehyde dehydrogenase by citral, a retinoid antagonist
Mechanism of inhibition of aldehyde dehydrogenase by citral, a retinoid antagonist
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DOI：
10.1046/j.1432-1327.1999.00415.x
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发表时间：
1999-06-01
期刊：
影响因子：
--
通讯作者：
Pietruszko, R
中科院分区：
文献类型：
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作者：
Kikonyogo, A;Abriola, DP;Pietruszko, R
低浓度的柠檬醛(3，7-二甲基-2，6-辛二烯醛)对人醛脱氢酶(EC 1.2.1.3)的EL、E_2和E_3同工酶有抑制作用。在NAD(+)存在下，这种抑制作用在稀释和长时间孵育时是可逆的；它与NADH和香叶酸的形成同时发生。因此，柠檬醛是一种抑制剂，也是一种底物。E_1、E_2和E_3的V-max分别为4U/M、1U/M和0.1U/M，E_1的V-max值最高(73nmol.min(-1)·mg(-1))，E_2居中(17nmol.min(-1)·mg(-1))，E3同工酶的V-max最低(0.07nmol.min(-1)·mg(-1))。柠檬醛是1：2异构体的混合物：顺式异构体和反式异构体，香叶醛；后者在结构上类似于重要的生理类维A酸。三种同工酶都利用了这两种异构体；通过高效液相色谱和酶动力学观察到对反式异构体天竺葵醛的偏好。在EL同工酶和E2同工酶中，只有NERAL符合Michaelis-Menten动力学。E_2同工酶和天竺葵乙状结肠饱和曲线的S-0.5值约为50 nM，n值为2-2.5时为正协同作用。Geranial是一种比Neral更好的底物和抑制剂。低V-max似乎受硫代半缩醛反应中间体缓慢形成或通过氢化物转移分解控制，使柠檬醛成为一种极好的缓蚀剂，其选择性因低K-m值而提高。具有E1同工酶的柠檬醛的V-max高于E2和E3同工酶，说明柠檬醛被抑制后恢复较快，提示EL-MAP是参与体内柠檬醛代谢的酶。
Low concentrations of citral (3,7-dimethyl-2,6-octadienal), an inhibitor of retinoic acid biosynthesis, inhibited El, E2 and E3 isozymes of human aldehyde dehydrogenase (EC 1.2.1.3). The inhibition was reversible on dilution and upon long incubation in the presence of NAD(+); it occurred with simultaneous formation of NADH and of geranic acid. Thus, citral is an inhibitor and also a substrate. K-m, values for citral were 4 mu M for E1, 1 mu M for E2 and 0.1 mu M for E3; V-max values were highest for E1 (73 nmol.min(-1).mg(-1)), intermediate for E2, (17 nmol.min(-1).mg(-1)) and lowest (0.07 nmol.min(-1).mg(-1)) for the E3 isozyme. Citral is a 1 : 2 mixture of isomers: cis isomer neral and trans isomer, geranial; the latter structurally resembles physiologically important retinoids. Both were utilized by all three isozymes; a preference for the trans isomer, geranial, was observed by HPLC and by enzyme kinetics. With the El isozyme, both geranial and neral, and with the E2 isozyme, only neral obeyed Michaelis-Menten kinetics. With the E2 isozyme and geranial sigmoidal saturation curves were observed with S-0.5 of approximate to 50 nM; the n-values of 2-2.5 indicated positive cooperativity. Geranial was a better substrate and a better inhibitor than neral. The low V-max, which appeared to be controlled by either the slow formation, or decomposition via the hydride transfer, of the thiohemiacetal reaction intermediate, makes citral an excellent inhibitor whose selectivity is enhanced by low K-m values. The V-max for citral with the E1 isozyme was higher than those of the E2 and E3 isozymes which explains its fast recovery following inhibition by citral and suggests that El map be the enzyme involved in vivo citral metabolism.