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Enzyme‐catalysed Transformations of Compounds Containing the –CH 2 ‐AsO 3 H 2 Group
Author(s) -
Dixon Henry B. F.,
Mutenda Esther K.,
Sparkes Michael J.
Publication year - 1997
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/(sici)1099-0739(199704)11:4<251::aid-aoc572>3.0.co;2-t
Subject(s) - chemistry , arsenite , phosphonate , enzyme , stereochemistry , substrate (aquarium) , cofactor , arsenate , biochemistry , organic chemistry , arsenic , oceanography , geology
Enzymes that act on substrates R–O–PO 3 H 2 often work on substrate analogues R–O–AsO 3 H 2 ; such substrates are unstable, since esters of H 3 AsO 4 hydrolyse easily. They also form easily, so that an enzyme that acts on R–O–PO 3 H 2 often acts on a mixture of R–OH and arsenate via an ester that forms at the active site. Similarly coenzyme analogues may be formed; for example, a stable and active aspartate aminotransferase forms from the apoenzyme with free pyridoxal and arsenate. Enzymes that convert R–O–PO 3 H 2 into a diester often act on R–CH 2 –AsO 3 H 2 , a stable substrate analogue; then the product is unstable and hydrolyses to re‐form the analogue, giving a futile cycle. For example, RNA polymerase acquires exonuclease activity in the presence of H 2 O 3 P–CH 2 –AsO 3 H 2 ; adenylate kinase acquires ATPase activity in the presence of the arsonomethyl analogue of AMP. A recent observation is that HO–CH 2 –CHOH–CH 2 –CH 2 –AsO 3 H 2 is a good substrate for glycerol‐3‐phosphate dehydrogenase. The product is unstable and eliminates arsenite, sharing this ability with other 3‐oxoalkylarsonates. Thus this enzyme–catalysed oxidation is a lethal synthesis, in view of the toxicity of arsenite. Another unusual biochemical reaction of an arsonic acid is seen in the ability of a bacterium to use arsonoacetate as its sole source of carbon and energy. In contrast with the elimination of arsenite by 3‐oxoalylarsonic acids, 3‐oxoalkylphosphonic acids, R–CO–CH 2 –CH 2 –PO 3 H 2 , are stable. 2‐Oxoalkylphosphonic acids, R–CO–CH 2 –PO 3 H 2 , however, are moderately unstable to hydrolysis, yielding phosphate and R–CO–CH 3 . 2‐Oxoalkylarsonic acids, R–CO–CH 2 –AsO 3 H 2 , decompose in the same way, but much more readily, yielding arsenate. © 1997 by John Wiley & Sons, Ltd.