A simple method for the isolation of crystalline D-hamamelose

Conversion of D-hamamelose into 2-carboxy-D-arabinitol and 2-carboxy-D-arabinitol 1-phosphate in leaves of Phaseolus vulgaris L

[1-14C]Hamamelose (2-hydroxymethyl-D-ribose) was synthesized by reaction of ribulose 5-phosphate with potassium [14C]cyanide, catalytic hydrogenation of the resulting cyanohydrin, and dephosphorylation of the product. Its identity was established by a chromatographic comparison with hamamelose isolated from the bark of witch hazel (Hamamelis virginiana L.). Following vacuum infiltration of the [1-14C]hamamelose into leaf discs from Phaseolus vulgaris L., 14C-labeled 2carboxy-D-arabinitol (CA) and 2-carboxy-D-arabinitol 1-phosphate (CA1P) were formed, in the dark. Conversion of hamamelose to both CA and CA1P in the leaf discs was inhibited by dithiothreitol and sodium fluoride, although at high concentrations of these inhibitors conversion into CA was still evident when conversion into CA1P was totally inhibited. Wheat (Triticum aestivum L.) leaves converted hamamelose into CA without formation of CA1P. Leaves from P. vulgaris contained 68 nmol.g-1 fresh weight of hamamelose in the light and 35 nmol.g-1 fresh weight in the dark. A pathway for the biosynthesis of CA1P from Calvin cycle intermediates is proposed which includes the sequence: hamamelose --> CA --> CA1P.

Purification and properties of hamamelosekinase

Hamamelosekinase (ATP:hamamelose 2(1)-phosphotransferase) was purified from a crude extract of Kluyvera citrophila 627 (Enterobacteriaeceae) which has been grown on D-hamamelose. Ammonium-sulfate fractionation and twofold chromatography on DEAE-cellulose resulted in a 51-fold purification of the enzyme. Neither glucosekinase nor significant ATPase activity could be detected in the pure preparation. Besides D-hamamelose only D-hamamelitol was utilized as a substrate; however, the latter was phosphorylated at a very low rate. The molecular weight of the enzyme as estimated by gel chromatography is 21 000. The Km values for hamamelose and ATP were 3 mM nd 2.5 mM, respectively. The pH optimum was found at 7.5. In contrast to hexokinase, purified hamamelosekinase is very labile and could only be stabilized by addition of its substrate D-hamamelose. The most unusual property with respect to yeast hexokinase is a pronounced substrate inhibiton by hamamelose (> 5mM) and ATP (> 7mM), respectively, which could be interpreted as due to an economic utilization of the nutrient. Hamamelosekinase as well as glucosekinase are inducible by growing the microorganisms on the corresponding monosaccharides.