198
G. L. CANTONI
role. Carnitine can undergo reversible biological acetylation (Eq. 9)
by means of an enzyme isolated from pigeon liver (62):
Carnitine + Acetyl-CoA ±+ O-Acetyl carnitine + CoA
(9)
Since the reaction is readily reversible, if the enzyme catalyzing it
were found also in muscle this pathway might indicate a function for
carnitine as storehouse of energy-rich acetyl groups. Another and possibly significant lead on the biochemical function of carnitine is the
finding of Fritz (63), that carnitine in concentrations as low as
6 X 10
-5 M increases the oxidation of palmitic acid by liver homogenates, and more specifically stimulates the formation of ketone bodies
from higher fatty acids. The exact role played by carnitine in oxidation of higher fatty acids is not yet understood but it may be hoped
that progress in this direction will be rapid as the field is an active one
in biochemistry.
Nothing is known about the two betaines structurally related to
carnitine, except that they are naturally occurring and, especially butyrobetaine, are found widely distributed both in invertebrates and in
vertebrates (64). γ-Butyrobetaine is the only carnitine analog which
competitively inhibits the utilization of carnitine by Tenebrio molitor
(60).
4. Ercinine and Ergothioneine
Very little is known about ercinine but ergothioneine has received
considerable interest among biochemists in recent years and its occurrence, distribution, biogenesis, and possible metabolic role will be
discussed in some detail [see also Bell (65)].
a. Origin and Distribution. As implied by its name, ergothioneine
was originally isolated and identified as a constituent of the ergot of
rye by Tanret (66), and Barger and Ewins (67). In ergot it is found
in concentrations as high as 250 mg./100 gm. No other source of this
material was known until ergothioneine was discovered in pig blood
(68) where its distribution is exclusively intracellular, being confined
to the erythocytes. The content of ergothioneine in blood is very much
smaller than in ergot and varies in different vertebrates between 1 and
5 mg./100 ml. (69). In the rat, at least, ergothioneine is not confined to
red blood cells and several other tissues contain it in small amounts
(70). Interest in this compound was revived in recent years as the result of the discovery by Mann and Leone (71) that this thiolbetaine is
a normal constituent of boar semen into which it is secreted by the
seminal vesicles. The concentration of ergothioneine in semen is particularly high, in some instances approaching the levels found in ergot.
G. L. CANTONI
role. Carnitine can undergo reversible biological acetylation (Eq. 9)
by means of an enzyme isolated from pigeon liver (62):
Carnitine + Acetyl-CoA ±+ O-Acetyl carnitine + CoA
(9)
Since the reaction is readily reversible, if the enzyme catalyzing it
were found also in muscle this pathway might indicate a function for
carnitine as storehouse of energy-rich acetyl groups. Another and possibly significant lead on the biochemical function of carnitine is the
finding of Fritz (63), that carnitine in concentrations as low as
6 X 10
-5 M increases the oxidation of palmitic acid by liver homogenates, and more specifically stimulates the formation of ketone bodies
from higher fatty acids. The exact role played by carnitine in oxidation of higher fatty acids is not yet understood but it may be hoped
that progress in this direction will be rapid as the field is an active one
in biochemistry.
Nothing is known about the two betaines structurally related to
carnitine, except that they are naturally occurring and, especially butyrobetaine, are found widely distributed both in invertebrates and in
vertebrates (64). γ-Butyrobetaine is the only carnitine analog which
competitively inhibits the utilization of carnitine by Tenebrio molitor
(60).
4. Ercinine and Ergothioneine
Very little is known about ercinine but ergothioneine has received
considerable interest among biochemists in recent years and its occurrence, distribution, biogenesis, and possible metabolic role will be
discussed in some detail [see also Bell (65)].
a. Origin and Distribution. As implied by its name, ergothioneine
was originally isolated and identified as a constituent of the ergot of
rye by Tanret (66), and Barger and Ewins (67). In ergot it is found
in concentrations as high as 250 mg./100 gm. No other source of this
material was known until ergothioneine was discovered in pig blood
(68) where its distribution is exclusively intracellular, being confined
to the erythocytes. The content of ergothioneine in blood is very much
smaller than in ergot and varies in different vertebrates between 1 and
5 mg./100 ml. (69). In the rat, at least, ergothioneine is not confined to
red blood cells and several other tissues contain it in small amounts
(70). Interest in this compound was revived in recent years as the result of the discovery by Mann and Leone (71) that this thiolbetaine is
a normal constituent of boar semen into which it is secreted by the
seminal vesicles. The concentration of ergothioneine in semen is particularly high, in some instances approaching the levels found in ergot.