Question

Biochemistry question: Arsenate (AsO4 3- ) closely resembles inorganic phosphate (Pi) in structure and reactivity. In the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase, arsenate can replace phosphate in attacking the energy-rich thioester intermediate in the enzymatic mechanism. The product of this reaction is both thermodynamically and kinetically unstable leading to spontaneous hydrolysis of the acyl arsenate in the presence of water.

a) What is the net reaction of the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase in the presence of arsenate instead of Pi?

b) What would be the effect of arsenate on the energy generation of a cell? Describe your answer in terms of why arsenate is very toxic to most organisms.

Answer 1

a) In the existence of arsenate, the net reaction will be:

Glyceraldehyde-3-phosphate + NAD+ + H2O → 3-phosphoglycerate + NADH + 2H+

b) The arsenate would result in the uncoupling of phosphorylation and oxidation by resulting in the generation of an acyl arsenate compound, which is extremely labile. The condition is also termed as arsenate poisoning. It is a condition, which results because of the enhanced concentration of arsenic in the body. In the condition, a person may experience abdominal pain, vomiting, watery diarrhea, and encephalopathy.