Differential Effects of Mg2+ Ions on the Individual Kinetic Steps of Human Cytosolic and Mitochondrial Aldehyde Dehydrogenases

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• 作者：Kwok Ki Ho ; Abdellah Allali-Hassani ; Thomas D. Hurley ; and Henry Weiner
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：June 7, 2005
• 年：2005
• 卷：44
• 期：22
• 页码：8022 - 8029
• 全文大小：200K
• 年卷期：v.44,no.22(June 7, 2005)
• ISSN：1520-4995

文摘

Although the structures of mammalian cytosolic and mitochondrial ALDH have beendetermined, several differences, mainly functional, between these two 70% identical isozymes remainunexplained. A major difference is the differential effect of Mg²⁺ ions that inhibits the cytosolic andactivates the mitochondrial isozyme. Here, we have investigated the effect of Mg²⁺ ions on each individualkinetic step of ALDH1 and ALDH2. The metal ions were found not to affect either acylation or hydridetransfer for either isozyme. The lack of a Mg²⁺ ion effect on hydride transfer was further demonstratedwith an E399Q mutant of ALDH1 whose rate-limiting step had been changed from NADH dissociationto hydride transfer. The other steps, however, were affected by Mg²⁺ ions for both isozymes. The metalions inhibited NADH dissociation, the rate-limiting step for ALDH1, and enhanced deacylation, the rate-limiting step for ALDH2. Our results indicated that, with both isozymes, Mg²⁺ ions tightened the bindingof NADH, and by binding to the coenzyme, they increased the nucleophilicity of the nucleophile Cys302.The inhibition of ALDH1 and activation of ALDH2 at pH 7.4 are due to their different rate-limitingsteps. Mg²⁺ ions affected similarly the NADH activation of the esterase reaction for both isozymes. Incontrast, the metal ions affected only the NAD⁺ activation of ALDH1. This latter finding and other featuresdescribed here can be rationalized on the basis of the known three-dimensional structures of the isozymes.