TABLE 1.

Elements known to exist in alkylated form within biological systems or produced by biological activity^a

Element	Enzyme or system	Reference
Specific
H	Methyl-S-coenzyme M reductase	54
C	Acetyl coenzyme A synthase	73
N	Phospholipid N-methyltransferase	139
O	S-Adenosylmethionine methyltransferase	30
F	Streptomyces sp.	93
P	Methylcobalamin	112
S	S-Adenosylmethionine methyltransferase	5
Cl	Various fungi and algae	48
Co	Methyl-B12	98
Ni	Methyl-S-coenzyme M reductase	36
Nonspecific
Cr	Cocorrinoids (in vitro only)	98
Cu	Cocorrinoids (in vitro only)	98
Ga	Cocorrinoids (in vitro only)	98
Ge	Methylgermanium in nature; source unknown	128
As	S-Adenosylmethionine methyltransferase	21
Se	S-Adenosylmethionine methyltransferase	100
Br	Marine phytoplankton	109
Rh	Propionibacterium shermanii	65
Pd	Methylcobalamin (in vitro only)	102
Cd	Polar marine bacteria	96
In	Cocorrinoids (in vitro only)	98
Sn	Saccharomyces cerevisiae	3
Sb	Scopulariopsis brevicaulis	55
Te	Pseudomonas fluorescens K27	7
I	S-Adenosylmethionine methyltransferase	1
Pt	Methylcobalamin (in vitro only)	37
Au	Methylcobalamin (in vitro only)	102
Hg	Desulfovibrio desulfuricans LS	25
Tl	Anaerobic bacteria from freshwater sediment	110
Pb	Bacteria from lake sediment	108
Bi	Methanobacterium formicicum	81
Po	Marine sediment	83

^aElements are listed in order of increasing atomic number. Specific reactions are carried out by enzymes that selectively catalyze the alkylation; others may be fortuitous.