422
ERNEST BUEDING AND EMMANUEL FÄRBER
A variety of fermentation products are formed by helminths. Many
of them produce lactic acid, but only rarely is the latter the exclusive or
even the major end product of carbohydrate metabolism, as in the case
of Schistosoma mansoni (41) and Dracunculus insignis (46). Volatile
fatty acids [acetic (50, 166), propionic (166, 167), n-valeric (168, 169),
a-methylbutyric (167), tiglic (167) acid, and one or several unidentified
C 6 -volatile acids (167, 169)], higher nonvolatile fatty acids (170-172),
succinic acid (170, 171, 173) and acetylmethylcarbinol (174, 175) have
been identified as products of the carbohydrate metabolism of parasitic
worms. In every species in which this problem has been studied, it has
been found that the Embden-Meyerhof scheme represents the major
pathway for the utilization of carbohydrate by helminths (167,176-181).
The occurrence of the pentose-phosphate route has been demonstrated
in Ascaris (182, 183), but the reported low activities of the enzymes involved in this pathway suggest that quantitatively the latter plays only
a minor role in the utilization of carbohydrate by Ascaris. It has not
been determined whether phosphogluconate can be metabolized in
helminths via 2-desoxy-3-keto-6-phosphogluconate.
No definite information is available about the mechanisms involved
in the formation of volatile acids or of succinic acid by helminths. It is
conceivable that pyruvate, produced by glycolytic reactions, is the common precursor of these acids. Recently it has been demonstrated that
α-acetolactate is formed from pyruvate by Ascaris muscle (175). As
illustrated below, the carbon skeleton of α-acetolactate is the same as
that of α-methylbutyric and tiglic acids which are fermentation products
of Ascaris. Saz et al. (175) have pointed out that these acids could be
formed from α-acetolactate by the sequence (I) of reactions shown.
CH 3
I
c=o
I
CH 3 —COH
I
COOH
a-Acetolactic
acid
+ DPNH
CH 3
I
HCOH
I
CH 3 —COH
-H 2 0
COOH
a, β-Dihy droxy-a-methylbutyric acid
CH 3
I
C=0
+DPNH
|
>
CH
CH;
COOH
a-Methylacetoacetic
acid
CH 3
I
HCOH
I
CH 3 —CH
-H 2 0
I
COOH
a-Methyl-jS-hydroxybutyric
acid
CH 3
I
H
II
CH 3 —C
I
COOH
Tiglic
acid
(I)
+H 2
CH 3
I
HCH
CH 3 —CH
COOH
a-Methylbutyric
acid
ERNEST BUEDING AND EMMANUEL FÄRBER
A variety of fermentation products are formed by helminths. Many
of them produce lactic acid, but only rarely is the latter the exclusive or
even the major end product of carbohydrate metabolism, as in the case
of Schistosoma mansoni (41) and Dracunculus insignis (46). Volatile
fatty acids [acetic (50, 166), propionic (166, 167), n-valeric (168, 169),
a-methylbutyric (167), tiglic (167) acid, and one or several unidentified
C 6 -volatile acids (167, 169)], higher nonvolatile fatty acids (170-172),
succinic acid (170, 171, 173) and acetylmethylcarbinol (174, 175) have
been identified as products of the carbohydrate metabolism of parasitic
worms. In every species in which this problem has been studied, it has
been found that the Embden-Meyerhof scheme represents the major
pathway for the utilization of carbohydrate by helminths (167,176-181).
The occurrence of the pentose-phosphate route has been demonstrated
in Ascaris (182, 183), but the reported low activities of the enzymes involved in this pathway suggest that quantitatively the latter plays only
a minor role in the utilization of carbohydrate by Ascaris. It has not
been determined whether phosphogluconate can be metabolized in
helminths via 2-desoxy-3-keto-6-phosphogluconate.
No definite information is available about the mechanisms involved
in the formation of volatile acids or of succinic acid by helminths. It is
conceivable that pyruvate, produced by glycolytic reactions, is the common precursor of these acids. Recently it has been demonstrated that
α-acetolactate is formed from pyruvate by Ascaris muscle (175). As
illustrated below, the carbon skeleton of α-acetolactate is the same as
that of α-methylbutyric and tiglic acids which are fermentation products
of Ascaris. Saz et al. (175) have pointed out that these acids could be
formed from α-acetolactate by the sequence (I) of reactions shown.
CH 3
I
c=o
I
CH 3 —COH
I
COOH
a-Acetolactic
acid
+ DPNH
CH 3
I
HCOH
I
CH 3 —COH
-H 2 0
COOH
a, β-Dihy droxy-a-methylbutyric acid
CH 3
I
C=0
+DPNH
|
>
CH
CH;
COOH
a-Methylacetoacetic
acid
CH 3
I
HCOH
I
CH 3 —CH
-H 2 0
I
COOH
a-Methyl-jS-hydroxybutyric
acid
CH 3
I
H
II
CH 3 —C
I
COOH
Tiglic
acid
(I)
+H 2
CH 3
I
HCH
CH 3 —CH
COOH
a-Methylbutyric
acid