Ix. the Synthesis of Reserve Carbohydrate by Yeast

THERE has been considerable discussion as to the best method to be adopted in isolating the reserve carbohydrate of yeast. In order to isolate the insoluble carbohydrate all other material of the cell must be brought into solution and with this object earlier workers have extracted yeast with solutions of KOH varying from 3 to 60 %. The residue contains the insoluble carbohydrate whilst the soluble polysaccharides, glycogen and gum, may be precipitated by alcohol from the diluted alkaline solution. Zechmeister & Toth [1934] used 3 % KOH followed by 3 % HCI and examined the residue left after washing with alcohol and ether. They showed that their residue was soluble in cold concentrated HCR, by which it was gradually hydrolysed to glucose, a reducing biose being formed as an intermediate product. Treatment with alkali and acid has been condemned by Sevag et al. [1935], who claim by repeated treatment with water and organic solvents to have isolated a soluble polysaccharide of which the insoluble carbohydrate isolated by Salkowski and other workers is a breakdown product. Zechmeister & Toth have effectively replied to these criticisms and we would point out that as glycogen and yeast gum were extracted from yeast by the action of water and separated by saturating their solution with ammonium sulphate [Harden & Young, 1902] it seems clear that the soluble carbohydrate of Sevag and his colleagues must have contained both yeast gum and glycogen. Later, in order to avoid the action of strong reagents, Zechmeister & Toth [1936] made use ofthe action ofenzymes to bring into solution the contents of the yeast cells and the findings of these workers as to the nature of the insoluble carbohydrate residue seem to be in harmony with our conclusions.