The Biochemistry of Arsenate

The Biochemistry of Arsenate A. Comparison of Arsenate with Phosphate 

Arsenic and phosphorus are adjacent members of the same group of the periodic table. Group 15 in the lUPAC numbering that avoids the earlier confusion of contradictory systems that gave it both designations 

The idea that enzymes whose normal substrate is orthophosphate can use arsenate in its place, and that the esters of arsenate formed are rapidly hydrolyzed, was given by Braunstein (i 6) in 1931, to explain the effects of arsenate on glycolysis. This idea was formulated more precisely for glyceraldehyde-phosphate dehydrogenase in 1939. This enzyme, E—SH, normally oxidizes its aldehyde substrate with phosphate uptake to give an acyl phosphate, as follows  

Arsenate similarly replaces phosphate in ATP synthesis, and the ATP analogue formed, a phosphorylated arsenate, has a similarly short lifetime, possibly up to a few seconds (13-15). R—COO might be expected to be a better leaving group than R—POa, since it is a weaker base. The arsenic compound analogue is capable of being trapped by hexokinase, since the glucose 6-arsenate formed is much more stable (12). 

The lability of esters of arsenate is of course mirrored in their ease of formation. Hence, merely mixing an alcohol with arsenate leads to 

Arsenate similarly replaces phosphate in various phosphorolysis reactions, so that sucrose phosphorylase catalyzes the hydrolysis of sucrose in its presence (23), potato phosphorylase can hydrolyze amylose and amylopectin (24), nucleoside phosphorylase can hydrolyze inosine 

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To review the older literature dealing with the biochemistry of arsenic, the reader is referred to two books and the excellent reviews by Webb , Fowler and Zingaro and Bottino (an article in Reference 4). 

FC Knowles, AA Benson. The biochemistry of arsenic. Trends Biol Sci May 178-180 1983. 

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