In enzymology, a phosphopantothenateâÂÂcysteine ligase also known as phosphopantothenoylcysteine synthetase (PPCS) is an enzyme () that catalyzes the chemical reaction which constitutes the second of five steps involved in the conversion of pantothenate to Coenzyme A. The reaction is:
The nucleoside triphosphate (NTP) involved in the reaction varies from species to species. PhosphopantothenateâÂÂcysteine ligase from the bacterium Escherichia coli uses cytidine triphosphate (CTP) as an energy donor, whilst the human isoform uses adenosine triphosphate (ATP).
This enzyme belongs to the family of ligases, specifically those forming carbon-nitrogen bonds as acid-D-amino-acid ligases (peptide syntheses). The systematic name of this enzyme class is (R)-4'-phosphopantothenate:L-cysteine ligase. This enzyme is also called phosphopantothenoylcysteine synthetase.
Phosphopantothenoylcysteine synthetase in humans is encoded by the PPCS gene.
As of late 2007, 5 structures have been solved for this class of enzymes, with PDB accession codes , , , , and .