(a) Predict the effect on the net reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase if phosphate were replaced by arsenate

Question

Also, What would be the consequence to an organism if arsenate were substituted for phosphate? Arsenate is very toxic to most organisms. Explain why.

Answer 1

(a) Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is an enzyme involved in the glycolytic pathway that catalyzes the conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate, with the concomitant reduction of NAD+ to NADH. The reaction involves the transfer of a phosphate group from glyceraldehyde 3-phosphate to NAD+, forming NADH and 1,3-bisphosphoglycerate.

If phosphate were replaced by arsenate in the reaction catalyzed by GAPDH, the net reaction would be inhibited. This is because arsenate can mimic phosphate and bind to the active site of GAPDH, but it cannot participate in the catalytic reaction in the same way as phosphate. Arsenate has a lower affinity for the enzymes that use phosphate as a substrate, so it would compete with phosphate and inhibit the enzyme's activity. As a result, the conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate would be impaired, and the rate of glycolysis would be decreased.

(b) If arsenate were substituted for phosphate in an organism, it would disrupt many essential biological processes that depend on phosphate. Phosphate is involved in the synthesis of DNA and RNA, the formation of ATP, and the regulation of many enzymes. Arsenate can mimic phosphate and bind to enzymes and other proteins that use phosphate, but it cannot be used in these processes in the same way as phosphate. As a result, the substitution of arsenate for phosphate would impair the functioning of many enzymes and proteins, leading to metabolic disruption and cellular damage. This is why arsenate is very toxic to most organisms.

Arsenate is toxic because it interferes with cellular metabolism and inhibits the activity of many essential enzymes that depend on phosphate. Arsenate can replace phosphate in many biological reactions, but the resulting arsenate-containing compounds are unstable and cannot be used in the same way as the corresponding phosphate-containing compounds. As a result, the substitution of arsenate for phosphate can lead to metabolic disruption and cellular damage, which can ultimately lead to cell death.