The number of substrate-level phosphorylation in one turn of citric acid cycle is:

Substrate-level phosphorylation: In the presence of the enzyme succinyl CoA synthetase or succinyl thiokinase, succinyl CoA is converted into succinate, producing GTP as the source of energy. This GTP then in the presence of phosphokinase gets converted into ATP.

$\mathrm{Succinyl} \mathrm{CoA} + \mathrm{GDP} + \mathrm{Pi} \stackrel{\mathrm{Succinyl} \mathrm{CoA} \mathrm{synthetase}/\mathrm{Succinyl} \mathrm{thiokinase}}{\to } \mathrm{Succinate} + \mathrm{GTP} + \mathrm{CoA}$