Detection and properties of l-histidinol dehydrogenase in wheat germ

Abstract

The presence and partial characterization of the properties of l-histidinol dehydrogenase (EC 1.1.1.23), the enzyme catalysing the last step in the pathway of histidine biosynthesis, has been described in higher plants for the first time. The activity has been found in cell-free extracts from wheat germ, turnip root, radish root and squash fruit. The enzyme has been partially purified and characterized from extracts of acetone powders of wheat germ. DEAE-cellulose chromatography revealed two peaks of histidinol dehydrogenase activity. In one there was a rapid reduction of NAD + in the absence of histidinol; however, the rate was stimulated by the addition of histidinol. The rate in the absence of substrate became quite low after several min and the histidinol-dependent rate was then easily observed. The second peak of activity did not reduce NAD + unless l-histidinol was present in the assay mixture. The K m s for l-histidinol and NAD + were determined for this latter enzyme. The values obtained at saturating concentrations of the other substrate were l-histidinol, 8.8 μM and NAD +, 0.14 mM. The product of the dehydrogenase reaction was histidine as determined by paper chromatography.