Moiety conservation is the conservation of a subgroup in a chemical species, which is cyclically transferred from one molecule to another.
Example
Adenosine diphosphate (ADP) is a subgroup that remains unchanged when it is phosphorylated to create adenosine triphosphate (ATP) and then unphosphorylated back to ADP forming a conserved cycle. Moiety-conserved cycles in nature exhibit unique network control features which can be elucidated using techniques such as metabolic control analysis.
References
Moiety conservation Wikipedia(Text) CC BY-SA