Chymosin

and then levels off to a concentration which is about half of the maximum [10]. Nothing is known about its function; pepsinogen B has never been found in species other than pig and dog, in spite of intensive research on gastric extracts from cow and human. However, pepsinogen B accounts for 30% of the total pepsinogen level in dog gastric mucosa indicating a dominating role in digestion [7]. Some databases have mis-registered opossum progastricsin (Q689Z7) as pepsin B and the name has been used incorrectly in rattail for what presumably is a pepsin [4].