226
G. L. CANTONI
age of intermolecular disulfide bonds. The possible biological significance
of the polymerization reaction is at present obscure; it would be of the
greatest interest to investigate enzymes with similar functions derived
from sources other than horse liver to see if they would show similar
physicochemical characteristics.
2. Alkyl Transfer Reactions from
S-Adenosylmethionine
S-Adenosylmethionine is known to participate as a methyl donor in
the enzymatic reaction involved in the synthesis of creatine (183) N'methylnicotinamide (174,184) choline from dimethylethanolamine (17),
epinephrine from norepinephrine (185), 3-methoxy epinephrine from
epinephrine (186), ergosterol [(187), see also reference 188)] and 6methylamino-2-hydroxyadenine (189). On the basis of these findings it
may be suggested that S-adenosylmethionine is the actual methyl donor
in all biological methylation reactions in which the methyl group is
derived from methionine. However, it should be pointed out that there
is no positive evidence to indicate that adenosylmethionine is actually
involved in the numerous methylation reactions discovered in the plant
kingdom, and an equally tenable supposition would postulate that Smethylmethionine or some other methyl-onium compound is the methyl
donor.*
An important extension of the role originally envisaged for Sadenosylmethionine has been recently brought about by the discovery
that S-adenosylmethionine, after decarboxylation, can act as a donor of
its propylamine side chain to putrescine, and probably to spermine, for
the biosynthesis of spermine and spermidine respectively (190, 191).
Although no metabolic or enzymatic reactions suggesting that adenosylmethionine might function also as an adenosyl donor have been
discovered as yet, it is entirely reasonable to assume such a role for this
compound. In this case, then, adenosylmethionine could act as a donor
of any one of the three groups attached to the sulfonium center, depending on the specificities of the transferring enzymes and the acceptor
molecule.
As noted above guanidinoacetate methylpherase is specific for one
of the two stereoisomers of S-adenosyl-L-methionine, namely the ( — )S-adenosyl compound. Two other enzymes utilizing adenosylmethionine
* Note added in proof: Since this chapter was written Mudd (192) in the
author's laboratory has conclusively shown that (—) S-adenosyl-L-methionine is the
actual methyl donor in several plant transmethylation reactions. It may therefore
be assumed that S-adenosylmethionine is the methyl donor in all biological methylation reactions in which the methyl group is derived from methionine. The biochemical role of S-methylmethionine still remains obscure.
G. L. CANTONI
age of intermolecular disulfide bonds. The possible biological significance
of the polymerization reaction is at present obscure; it would be of the
greatest interest to investigate enzymes with similar functions derived
from sources other than horse liver to see if they would show similar
physicochemical characteristics.
2. Alkyl Transfer Reactions from
S-Adenosylmethionine
S-Adenosylmethionine is known to participate as a methyl donor in
the enzymatic reaction involved in the synthesis of creatine (183) N'methylnicotinamide (174,184) choline from dimethylethanolamine (17),
epinephrine from norepinephrine (185), 3-methoxy epinephrine from
epinephrine (186), ergosterol [(187), see also reference 188)] and 6methylamino-2-hydroxyadenine (189). On the basis of these findings it
may be suggested that S-adenosylmethionine is the actual methyl donor
in all biological methylation reactions in which the methyl group is
derived from methionine. However, it should be pointed out that there
is no positive evidence to indicate that adenosylmethionine is actually
involved in the numerous methylation reactions discovered in the plant
kingdom, and an equally tenable supposition would postulate that Smethylmethionine or some other methyl-onium compound is the methyl
donor.*
An important extension of the role originally envisaged for Sadenosylmethionine has been recently brought about by the discovery
that S-adenosylmethionine, after decarboxylation, can act as a donor of
its propylamine side chain to putrescine, and probably to spermine, for
the biosynthesis of spermine and spermidine respectively (190, 191).
Although no metabolic or enzymatic reactions suggesting that adenosylmethionine might function also as an adenosyl donor have been
discovered as yet, it is entirely reasonable to assume such a role for this
compound. In this case, then, adenosylmethionine could act as a donor
of any one of the three groups attached to the sulfonium center, depending on the specificities of the transferring enzymes and the acceptor
molecule.
As noted above guanidinoacetate methylpherase is specific for one
of the two stereoisomers of S-adenosyl-L-methionine, namely the ( — )S-adenosyl compound. Two other enzymes utilizing adenosylmethionine
* Note added in proof: Since this chapter was written Mudd (192) in the
author's laboratory has conclusively shown that (—) S-adenosyl-L-methionine is the
actual methyl donor in several plant transmethylation reactions. It may therefore
be assumed that S-adenosylmethionine is the methyl donor in all biological methylation reactions in which the methyl group is derived from methionine. The biochemical role of S-methylmethionine still remains obscure.