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206 THE CARBOHYDRATES.
and then from this by loss of CO2 the alcohol is derived. The ammonia
is assimilated by the yeast. If the amino-acid is in the racemic form
then only the one component occurring naturally is transformed into
alcohol while the other remains in great part unchanged. In this manner
leucine is converted into isoamylalcohol according to the following equa-
tion:
hoco.ch(nh2 ).ch2 .ch/
3
+h2 o=
Leucine XCH3
/CH3
NH3 +C02 +HOCH2 .CH2 .CH<
Isoamylalcohol ^P’TJo
Other examples of the same kind is the formation of d-amylalcohol
from d-isoleucine and of isobutylalcohol from a-amino-valeric acid.
The formation of higher alcohols takes place with yeast poor in nitrogen
and in the presence of large amounts of sugar. In an analogous man-
ner, under the influence of yeast in the presence of sugar and inor-
ganic nutritive salts, from tyrosine tyrosol (p-oxyphenylethyl alcohol)
HO.C6H4 .CH2 .CH2 .OH is derived and from tryptophane we get tryptophol
(/3-indoxylethyl alcohol) 1
.
C.CH2 .CH2 OH
C6H4<f%CH
NH
Other fermentation processes which are brought about by yeast but without
the presence of sugar have been studied by Neuberg 2
and his collaborators.
Among these we will mention the decomposition of pyroracemic acid (pyruvic
acid) into carbon dioxide and acetaldehyde
:
HO.CO.CO.CH3 =C02 +HOC.CH3 .
The enzyme active in this fermentation is called carboxylase. If the pyro-
racemic acid exists in the form of an alkali salt then the cleavage takes place ac-
cording to the formula,
2KO.CO.CO,CH3 +H20=C02 +2HOC.CH3 +K2 C03
and alkali carbonate is formed from a neutral salt. In this case the aldehyde
is condensed by the alkali to aldol, the first polymerization product of acetaldehyde.
The previously mentioned (page 41) lactic acid fermentation of
various sugars is caused by the action of different varieties of bacteria.
The equation represents a cleavage of one hexose molecule into two
lactic acid molecules CV,H 12 G = 2HOCO.CH(OH).CH3 . Nothing positive
1
Ber. d. d. chem. Gesellsch., 44, 139 (1910); 45, 883 (1912).
s
Bioch. Zeitschr., 31, 170 (1910); 32, 323; 36, 60, 68, 76 (1911); 47, 405, 413 (1912).
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