 Adenylyl group

An adenylyl group is the adenosine monophosphate-derived portion transferred in an adenylyl-transfer reaction. It includes the adenosine unit and one phosphorus-containing group; it is not simply adenine detached from its ribose. The IUBMB recommends adenylyl, rather than adenyl, for nucleotide groups.^[ref]

A concrete example is FAD synthase, whose systematic name is ATP:FMN adenylyltransferase. It transfers an ATP-derived adenylyl portion to flavin mononucleotide, forming flavin adenine dinucleotide and releasing diphosphate:The reaction identifies which part of ATP is incorporated, rather than merely recording ATP consumption.^[ref]

An original bookkeeping example makes the distinction visible. Complete conversion of 10 nmol of flavin mononucleotide using 20 nmol of ATP, with no side reactions, gives 10 nmol each of flavin adenine dinucleotide and diphosphate, leaving 10 nmol of ATP. The initial phosphorus inventory is $3(20)+1(10)=70$ nmol of phosphorus atoms; the final inventory is $2(10)+2(10)+3(10)=70$. Conservation checks the accounting but cannot, by itself, identify the products.