Figure 2. Three chokepoints generate orphan enzymes.

Starting from an enzyme activity that has been characterized in the lab (gray), there are three major chokepoints that can lead to enzyme activity not being linked to sequence data, generating an orphan enzyme (yellow) rather than a sequenced enzyme with an associated EC number (purple). In the laboratory stage, an enzyme may not be sequenced due to issues such as complexity of the sequencing process for that enzyme, a loss of researcher interest, or inadequate funds to pursue sequencing. When an enzyme has been sequenced, sequence data may not be deposited in GenBank and other major sequence databases, despite the presence of sequence data in a scientific publication. Finally, errors in depositing the sequence with those databases can prevent connection of that sequence data with the enzyme activity (see FIGURE 5).