POLYSACCHARIDE-PROTEIN COMPLEXES 207 



glucan was characterized as a presumably closed-chain polvmer of 

 yS-l,3-glucosido-gliicopvranose units. 



The structure of yeast glucan was reinvestigated by Bell and 

 Northcote (1950). Mildlv acidic conditions (0.5 N acetic acid), in 

 place of strong mineral acid, were employed to effect isolation of the 

 polymer, and chromatographic procedures were used to detect hy- 

 drolysis products following exhaustive methylation (former methods 

 relied on refractive indices and methoxyl content of the fractions 

 obtained by distillation of the hvdrolvzed methvlated glucan ) . With 

 these refinements, 2,3,4, 6-tetramethvl-D-glucose and 4,6-dimethyl-D- 

 glucose were detected, in addition to 2,4,6-trimethyl-D-glucose, as 

 products of hydrolysis of the methylated glucan. The methylated 

 derivatives of D-glucose were present in a ratio of tetra:di:tri 

 = 1:1:9, thus necessitating a drastic revision of the structural for- 

 mula that could be considered for glucan. Bell and Northcote 

 considered the polymer to be a highly branched structure in which 

 each unit chain consists, on the average, of nine anhvdroglucose 

 radicals. 



Glucomannans of Yeast. Early studies on the so-called yeast 

 gum showed it to contain glucose and mannose. Purified prepara- 

 tions with [ajo"^' — +88.5° were obtained by Salkowski (1894a), 

 Meigen and Spreng (1908), and von Euler and Fodor (1911). 



The preparation obtained by Meigen and Spreng had a ratio of 

 mannose : glucose = 2:1, whereas that of von Euler and Fodor 

 showed a ratio of 1:1. In the latter case, the gum was obtained by 

 extracting fat-free yeast with boiling water, or by precipitating the 

 polysaccharide with ethanol from an autolysate of brewers' yeast. 

 The polysaccharide was purified by repeated precipitation of the 

 copper complex, according to the technique of Salkowski, and sub- 

 sequent dialysis. It should be noted that treatment with hot alkali 

 was avoided. Quantitative analyses for mannose in the presence of 

 glucose in acid hydrolysates of the polysaccharide were carried out 

 by differential precipitation of the mannose phenylhydrazone. 



Subsequent investigations by Harden and Young (1912) and by 

 Ling et at. ( 1925 ) employed an extraction step involving boiling 2 

 per cent NaOH, and subsequent treatment of the alcohol-precipi- 

 table material with 60 per cent KOH for 2 hours in a vigorously 

 stirred boiling-water bath. 



The structure of a yeast mannan that was presumed to yield only 

 D-mannose on acid hydrolysis was studied by Haworth and collab- 



