R. MONTGOMERY AND F. SMITH
2834 [COSTRIBUTION FROM T f i E
DEPARTMEVT O F AGRICULTURAL
T’ol. 7 ;
BrOCHEMlSTRY, UVrVERSITY O F hfINNESOTA]
The Carbohydrates of Gramineae. V. The Constitution of a Hemicellulose of the Endosperm of Wheat (Triticum Vulgare)l * * BY R. MONTGOMERY AND F. SMITH RECEIVED DECEMBER 1, 1954 The constitution of a hemicellulose from the ”squeegee” fraction of wheat Aour has b x n investigated by methylation itudies. The methylated hemicellulose gives upon hydrolysis 2,3,5-tri-O-methyl-~-arabofurdnose(14 moles), 2,3-di-Omethyl-D-xylose (24 moles), %O-methyl-~-xylose(7 moles) and D-xylose ( 4 moles) together with small amounts of two unknown products. The highly branched structure of this hemicellulose conforms to the general type of structure found for the hemicelluloses of the endosperm of the Grawrineae.
When wheat flour, freed from gluten, is sus- carried out by the phenol-sulfuric acid procedure.8 pended in water and centrifuged, it separates into a In periodate oxidation studies, 0.8 mole of periodate tightly packed lower layer of wheat starch above was consumed per anhydropentose residue. The which is a mucilaginous material. The latter, resulting hemicellulose polyaldehyde after reducwhich has been variously called the “amylo- tion with hydrogen using a Kaney nickel catalyst d e ~ t r i n ”or~ “ s q ~ e e g e e ”or ~ tailing^"^ of wheat followed by acid hydrolysis of the polyalcohol gave flour, plays an important role in the starch-gluten a hydrolysate which was shown by chromatoseparation process. The chemical composition of graphic analysis to contain D-XylOSe. The hemithe squeegee fraction of wheat starch has not been cc,llulose thus appeared from the periodate studies extensively studied but it is known to contain starch to have a branched structure. granules and a considerable amount of pentosan In order to determine the mode of union of the and proteinaceous material. component sugars, the hemicellulose was methylThis paper is concerned with the composition ated with 45% potassium hydroxide and methyl and structure of a hemicellulose of the “squeegee” sulfate. Fractional precipitation of the methylated fraction of wheat flour. By the prolonged hy- hemicellulose from an acetone-ether solution with drolysis of the “squeegee” material with pancreatin petroleum ether gave a series of fractions, the D until i t no longer gives a color with iodine, Simpson6 properties of which were constant ( [ O ( ] ~ ?-1Cici” has obtained a water-insoluble product amounting in acetone and -0CH3, 38.8) indicating that the to 0.5-1y0 of the whole wheat flour. This insoluble methylated hemicellulose was essentially homomaterial was used in the present study. It was geneous. One striking property of the methylated fractionated by forming the acetate and separating hemicellulose was the highly viscous nature of its it into an acetone soluble fraction, showing [CY]“D solutions in acetone. Xethanolysis of the methylated hemicellulose 17” in pyridine, and an acetone-insoluble fraction which could not be dissolved in any of the common with 2% methanolic hydrogen chloride gave a solvents. Deacetylation of the acetone-insoluble mixture of glycosides which was hydrolyzed with fraction, which amounted to about 707, of the dilute hydrochloric acid to give the corresponding crude acetate, was achieved by heating a pyridine methylated reducing sugars. Chromatography on dispersion of it with 25% potassium hydroxide. a cellulose-hydrocellulose column l o using methyl The resulting material was purified by extraction ethyl ketone-water azeotrope as the developing with .V sodium hydroxide to give a white amorphous solvent, coupled with the isolation of crystalline product which dissolved in hot water and showed derivatives, showed that this mixture of methylin 0.5 N sodium hydroxide, a value ated sugars consisted of 2,3,.5-tri-O-niethyl-L[ o ( ] ~ *-108” D 2-0-methylin close agreement with that ( [ c u ] ~-103” in N arabinose, 2,3-di-0-methyl-~-xylose, sodium hydroxide) shown by wheat straw hemi- D-xylose and D-xylose; by means of paper chromatography and the phenol-sulfuric acid analytical cellulose.’ Upon hydrolysis with acid, the purified hemi- methoda for determining sugars, the proportions of cellulose gave n-xylose (59%), L-arabinose (397,) these four cleavage products of the methylated and D-glucose ( 2 : ; ) the quantitative analysis being hemicellulose were found to be 14, 24, 7 and 4 moles, respectively. -1lthough these data do not (1) This paper, S o 3127, Scientific Journal Series, Agricultural Exallow a definite structure to be assigned to the polyperiment Station. University of Minnesota, is part of a report of resaccharide, i t is seen that a framework of D-XylOsearch done under contract with t h e U . S. Depariment of Agriculture and authorized by the Research and Marketing Act of 1946. T h e pyranose units linked through positions 1 and 4 contract was supervised by the Xorthern Utilization Research Branch is present. The presence of 2-O-methyl-~-xylose of the Agricultural Research Service Presented a t the 125th annual indicates that the carbohydrate polymer has a meeting of the A.C.S., Kansas City, Kansas, March, 1934. branched structure in which the side chains, (2) P a r t I V , R. Montgomery and F Smith, Cereal C h e m . . 31, 490 (1954). terminated by arabofuranose residues, are attached ( 3 ) R 31 Sandstedt, C. E. Jolitz and hf. J. Blish, ibid., 16, 780 to xylose units of the framework through position 3. (1930). The isolation of 7 moles of 2-O-methyl-D-xylose (4) K. A. Clendenning and D. E. Wright, Can. J. Research, 28F,390
+
(1950). ( 5 ) M. hl. McMasters and G . E. Hilbert, Cereal Chem (1914).
,
21, 3L8
( G ) F. J. Simpson, Con. J . dlicrobiol., 1, 131 (1954). (7) I. Ehrenthal, R. Montgomery and 1‘. Smith, THIS J O U R N A L , 76, 5509 (1954).
(8) hl. Dubois, K. Gilles. J. I
