A Lethal Toxic Substance for Brewing Yeast in Wheat and Barley

Abstract

It is shown that among various grains, wheat and barley contain in the endosperm a toxic substance to brewing yeast, and the substance is easily extracted with a dilute sulfuric acid solution. One unit of the toxicity is defined as the lowest amount of the extract which inhibits the yeast growth in 10 ml of wort medium. Two or more units of the toxicity not only inhibited the yeast growth, but also caused the death of yeast cells. Although the toxic effect was not observed when divalent metallic ions such as Ca²⁺, Zn²⁺ or Fe²⁺ were present at a concentration of 5 × l0⁻³ mole or more, the toxicity could be recovered by the addition of ethylene-diamine-tetra-acetate (EDTA). Genetic relationships on the content of the toxicity in wheat and barley and sensitivity of yeast strains to the toxicity are also presented.

Abstract

A toxic substance contained in wheat and barley causing death of brewing yeast was purified and isolated as a single protein. The molecular weight of the toxic substance was estimated to be 9800 by Archibald method. The substance was found to be a simple protein by amino acid analysis. The isoelectric point was higher than pH 10. The UV absorption spectrum showed λ_max 278 mμ. By the measurement of the circular dichroic spectrum, the α-helix content was estimated to be 34.5%. The toxic effect was easily inactivated by trypsin, but not by chymotrypsin and carboxypeptidase.