Proteases type XIII

Figure 6.2 Pepsin (top) and protease type XIII (bottom) cleavage preferences for myoglobin, IPMS, RACE, and KIT proteins. The preference ratio Is the number of fragments with the specified C-terminal amino acid divided by the total number of that specific amino acid In the protein. Reproduced with permission from [31]. 2008, American Chemical Society...

More recently, Engen s group also investigated a new aspartic protease from the stomach of the rice field eel (Monopterus albus Zuiew) and compared digestion efficiency and specificity to porcine pepsin and protease type XIII. They found unique cleavage specificity for rice field eel pepsin at Arg, Asp, and Gly [15]. 

Two other proteases have been commercialized by Sigma and used for such experiments. They both are extracts from fungi protease from. Rhizopus species (type XVIII), EC 3.4.23.6, optimum pH 3 and protease from Aspergillus saitoi (type XIII), EC 3.4.23.18, optimum pH 2.8. Several others were purified or overexpressed by groups developing the approach. 

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