What is the fine-grained topic of the following text: Function The Nudix superfamily is widespread among eucaryotes, bacteria, archaea and viruses and consists mainly of pyrophosphohydrolases that act upon substrates of general structure NUcleoside DIphosphate linked to another moiety, X (NDP-X) to yield NMP plus P-X. Only return the topic.
Nudix superfamily and its function as pyrophosphohydrolases