SUBSTRATE STEREOSPECIFICITY OF THE NAD-DEPENDENT MANNITOL DEHYDROGENASE FROM CELERY

Citation
Jmh. Stoop et al., SUBSTRATE STEREOSPECIFICITY OF THE NAD-DEPENDENT MANNITOL DEHYDROGENASE FROM CELERY, Phytochemistry, 43(6), 1996, pp. 1145-1150
Citations number
22
Categorie Soggetti
Plant Sciences
Journal title
ISSN journal
00319422
Volume
43
Issue
6
Year of publication
1996
Pages
1145 - 1150
Database
ISI
SICI code
0031-9422(1996)43:6<1145:SSOTNM>2.0.ZU;2-M
Abstract
The NAD-dependent mannitol dehydrogenase (MTD) of celery catalyses the interconversion of D-mannitol and D-mannose. This 1-oxidoreductase is uniquely different from all NAD-dependent polyol dehydrogenases descr ibed to date, which are 2-oxidoreductases. The stereospecificity of ma nnitol dehydrogenase was tested in the oxidative direction in the pres ence of polyol and NAD cofactor and in the reductive direction in the presence of aldose and NADH. The enzyme would be expected to show the same stereospecificity in either direction. The stereospecificity in t he reductive direction was tested by attempted reduction of all eight D- and L-pentoses and 15 of the 16 D- and L-hexoses. Stereospecificity in the oxidative direction was tested with the four pentitols and fou r of the hexitols. Mannitol dehydrogenase showed a marked preference f or aldopentose and aldohexose substrates with the same absolute config uration at C-2 as that of D-mannose. Reduction of L-idose by mannitol dehydrogenase was the only exception to the stated stereochemical pref erence among 23 aldoses and eight alditols tested. The sugar D-threose that occurs rarely in nature is a competitive inhibitor (K-i = 18 mM) of mannitol oxidation. The physiologically important hexitols, galact itol and glucitol, are oxidized by MTD to aldoses that are not metabol ized by higher plants. Copyright (C) 1996 Elsevier Science Ltd