Regardless of structural data supporting substrate activation and key interactions in the binding pocket, the biochemical role of A domains must still be confirmed. There are a wide variety of assays available to gain a better understanding of A domain function. Some assays measure the adenylation half-reaction, while others measure the ability of an activated substrate to be loaded onto an acceptor molecule or carrier protein. These assays also vary in their detection methods, and it is our hope that by compiling a list, other researchers will be able to select whichever method is best for them depending on the availability and access to different resources.