Succinyl-CoA synthetase (also called succinate-CoA ligase) is a key enzyme in the tricarboxylic acid (TCA) cycle that catalyzes the reversible conversion of succinyl-CoA to succinate. This reaction is unique because it is coupled with substrate-level phosphorylation, producing a nucleoside triphosphate molecule. However, the specific nucleoside triphosphate produced can vary depending on the organism and tissue.

This article explains which energy-rich molecule—ATP or GTP—is generated by succinyl-CoA synthetase in plant mitochondria during this reaction.

Succinyl-CoA Synthetase Reaction

The enzyme catalyzes the reaction:

$\text{Succinyl-CoA}+\text{NDP}+\text{Pi}\leftrightarrow \text{Succinate}+\text{CoA}+\text{NTP}$

• NDP: Nucleoside diphosphate (either ADP or GDP)

• NTP: Nucleoside triphosphate (either ATP or GTP)

This means the enzyme can produce either ATP or GTP depending on the specific isoform and organism.

ATP vs. GTP Production

• In mammals and many eukaryotes, including plants, succinyl-CoA synthetase predominantly produces ATP in mitochondria.

• In some organisms, such as certain bacteria and mammals (e.g., liver), the enzyme produces GTP instead.

Evidence for ATP Production in Plant Mitochondria

• Studies on plant mitochondrial enzymes indicate that succinyl-CoA synthetase produces ATP rather than GTP.

• This ATP generation contributes directly to the cell’s energy pool via substrate-level phosphorylation, complementing oxidative phosphorylation.

Summary Table

Conclusion

In plant mitochondria, succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate with the concomitant production of ATP via substrate-level phosphorylation.

Correct answer: (2) ATP