210
G. L. CANTONI
NH
—H
H
x
N
N —CH—CH(OH)—CH(OH)—CH—CH 2 —8—CH 3
I
()
1
CH 3
FIG. 9. S-Adenosyldimethylthetin.
Schlenk (136) that in certain bacterial species adenine C
14 exchanges
with the adenine moiety of adenosylmethionine as outlined in Eq. 11.
Adenine-C
14 + S-Adenosylmethionine
<=± Adenine + *S-Adenosyl-C
14 -methionine
(11)
One chemical analogy of the cleavage under discussion is the alkaline
fission of 2-aroyloxethyldimethylsulfonium compounds (137) according
to Eq. 12.
CH3
CH3
©/
OH"
φ/
RCÜO—CH 2 —CH 2 —S
> R—COO- + CH 2 =CH—S
(12)
\
\
CH3
CH 3
Another analogy is seen in the report of Lawley that on mild hydrolysis (pH 7 and 37°) 7-methyldeoxyguanylic acid yields 7-methylguanine and deoxyribose-5-phosphate. The mechanism of the reaction
seems to involve the initial formation of 7-methyldeoxyguanosinium-5'phosphate (Fig. 10, I) or its isomer with the charge on N-9 (Fig. 10,
II), followed by elimination of the side chain (138).
At pH 4-7 and 100°, S-adenosylmethionine cleaves hydrolytically
and almost quantitatively with the formation of methylthioadenosine
and 2-amino-4-butyrolactone which under these conditions rapidly
hydrates to homoserine (129).
b. Natural Distribution. Although S-adenosylmethionine was first
discovered as the product of a reaction catalyzed by a liver enzyme,
this compound does not accumulate normally in the liver or other mammalian tissues to a measurable extent. On the other hand it has been
known for almost 50 years that yeast contains a sulfur nucleoside,
whose structure has been shown to be identical with methylthioadenosine (Fig. 11).* In fact the elucidation of the structure of S-adenosylmethionine has been greatly aided and stimulated by the previous
knowledge on the natural occurrence of methylthioadenosine. More recently the important work of Schlenk and his group emphasized the
fact that the thiomethyl group of methylthioadenosine originates from
the thiomethyl group in methionine (139; see also 140). Since under
* See references 138a and b.
G. L. CANTONI
NH
—H
H
x
N
N —CH—CH(OH)—CH(OH)—CH—CH 2 —8—CH 3
I
()
1
CH 3
FIG. 9. S-Adenosyldimethylthetin.
Schlenk (136) that in certain bacterial species adenine C
14 exchanges
with the adenine moiety of adenosylmethionine as outlined in Eq. 11.
Adenine-C
14 + S-Adenosylmethionine
<=± Adenine + *S-Adenosyl-C
14 -methionine
(11)
One chemical analogy of the cleavage under discussion is the alkaline
fission of 2-aroyloxethyldimethylsulfonium compounds (137) according
to Eq. 12.
CH3
CH3
©/
OH"
φ/
RCÜO—CH 2 —CH 2 —S
> R—COO- + CH 2 =CH—S
(12)
\
\
CH3
CH 3
Another analogy is seen in the report of Lawley that on mild hydrolysis (pH 7 and 37°) 7-methyldeoxyguanylic acid yields 7-methylguanine and deoxyribose-5-phosphate. The mechanism of the reaction
seems to involve the initial formation of 7-methyldeoxyguanosinium-5'phosphate (Fig. 10, I) or its isomer with the charge on N-9 (Fig. 10,
II), followed by elimination of the side chain (138).
At pH 4-7 and 100°, S-adenosylmethionine cleaves hydrolytically
and almost quantitatively with the formation of methylthioadenosine
and 2-amino-4-butyrolactone which under these conditions rapidly
hydrates to homoserine (129).
b. Natural Distribution. Although S-adenosylmethionine was first
discovered as the product of a reaction catalyzed by a liver enzyme,
this compound does not accumulate normally in the liver or other mammalian tissues to a measurable extent. On the other hand it has been
known for almost 50 years that yeast contains a sulfur nucleoside,
whose structure has been shown to be identical with methylthioadenosine (Fig. 11).* In fact the elucidation of the structure of S-adenosylmethionine has been greatly aided and stimulated by the previous
knowledge on the natural occurrence of methylthioadenosine. More recently the important work of Schlenk and his group emphasized the
fact that the thiomethyl group of methylthioadenosine originates from
the thiomethyl group in methionine (139; see also 140). Since under
* See references 138a and b.