1) Enzymes which transfer a group from one compound to another compound.

2) Transferases are enzymes transferring a group, for example, the methyl group or a glycosyl group, from one compound (generally regarded as donor) to another compound (generally regarded as acceptor). The classification is based on the scheme "donor: acceptor group transferase". (EC 2 class)

3) Enzymes that catalyze the transfer of functional groups between donor and acceptor molecules.