had previously led to the surmise that a genetic relation might exist between these substances, but the idea had not been experimentally confirmed. In 1903 Ehrlich discovered [[1903]; [1904, 1], [2]; [1907, 2]; [1908]; Ehrlich and Wendel, [1908, 2]] that proteins also yield on hydrolysis an isomeride of leucine known as isoleucine, which has the constitution
CH3·CH(C2H5)·CH(NH2)·COOH,
and therefore stands to d-amyl alcohol,
CH3·CH(C2H5)·CH2·OH,
in precisely the same relation as leucine to isoamyl alcohol. This suggestive fact at once directed his attention to the problem of the origin of the amyl alcohols in alcoholic fermentation. Using a pure culture of yeast, and thus excluding the participation of bacteria in the change, he found that leucine readily yielded isoamyl alcohol, and isoleucine d-amyl alcohol when these amino-acids were added in the pure state [p087] to a solution of sugar and treated with a considerable proportion of yeast [[1905]; [1906, 2], [3]; [1907, 1], [3]]. The chemical reactions involved are simple ones and are represented by the following equations:—
(1)
(CH3)2·CH·CH2·CH(NH2)·COOH
Leucine
+ H2O =
(CH3)2CH·CH2CH2·OH
Isoamyl alcohol
+ CO2 + NH3