A number of prokaryotic proteases have been shown [1,2] to be evolutionary related; their catalytic activity is provided by a charge relay system similar to that of the trypsin family of serine proteases but which probably evolved by independent convergent evolution. The sequence around the residues involved in the catalytic triad (aspartic acid, serine and histidine) are completely different from that of the analogous residues in the trypsin serine proteases and can be used as signatures specific to that category of proteases. The proteases which are known to belong to this family are listed below.

• Staphylococcus aureus V8 proteinase, which preferentially cleaves peptide bonds on the carboxyl-terminal side of aspartate and glutamate and which is widely used in protein sequencing studies.
• Bacillus licheniformis glutamate specific endopeptidase (GSE) [3], which like V8 cleaves on the carboxyl-terminal side of acidic residues, but with a strong preference for glutamate.
• Bacillus subtilis extracellular "metalloprotease" (gene mpr) [4].
• Staphylococcus aureus exfoliative (or epidermolytic) toxins A (gene eta) and B (gene etb). These toxins cause impetigous diseases commonly referred to as staphylococcal scalded skin syndrome (SSSS) and have been shown [1] to possess proteolytic activity.