Intrinsic alcohol dehydrogenase and hydroxysteroid dehydrogenase activities of human mitochondrial short-chain L-3-hydroxyacyl-CoA dehydrogenase

Citation
Xy. He et al., Intrinsic alcohol dehydrogenase and hydroxysteroid dehydrogenase activities of human mitochondrial short-chain L-3-hydroxyacyl-CoA dehydrogenase, BIOCHEM J, 345, 2000, pp. 139-143
Citations number
25
Categorie Soggetti
Biochemistry & Biophysics
Journal title
BIOCHEMICAL JOURNAL
ISSN journal
02646021 → ACNP
Volume
345
Year of publication
2000
Part
1
Pages
139 - 143
Database
ISI
SICI code
0264-6021(20000101)345:<139:IADAHD>2.0.ZU;2-Y
Abstract
The alcohol dehydrogenase (ADH) activity of human short-chain L-3-hydroxyac yl-CoA dehydrogenase (SCHAD) has been characterized kinetically. The k(cat) of the purified enzyme was estimated to be 2.2 min(-1), with apparent K-m values of 280 mM and 22 mu M for 2-propanol and NAD(+), respectively. The k (cat) of the ADH activity was three orders of magnitude less than the L3-hy droxyacyl-CoA dehydrogenase activity but was comparable with that of the en zyme's hydroxysteroid dehydrogenase (HSD) activity for oxidizing 17 beta-oe stradiol [He, Merz, Mehta, Schulz and Yang(1999) J. Biol. Chem. 274, 15014- 15019]. However, the k(cat) values of intrinsic ADH and HSD activities of h uman SCHAD were found to be two orders of magnitude less than those reporte d for endoplasmic-reticulum-associated amyloid beta-peptide-binding protein (ERAB) [Yan, Shi, Zhu, Fu, Zhu, Zhu, Gibson, Stern, Collison, Al-Mohanna e t al. (1999) J. Biol, Chem. 274, 2145-2156]. Since human SCHAD and ERAB app arently possess identical amino acid sequences, their catalytic properties should be identical. The recombinant SCHAD has been confirmed to be the rig ht gene product and not a mutant variant. Steady-state kinetic measurements and quantitative analyses reveal that assay conditions such as pH and conc entrations of coenzyme and substrate do not account for the kinetic differe nces reported for ERAB and SCHAD, Rather problematic experimental procedure s appear to be responsible for the unrealistically high catalytic rate cons tants of ERAB. Eliminating the confusion surrounding the catalytic properti es of this important multifunctional enzyme paves the way for exploring its role(s) in the pathogenesis of Alzheimer's disease.