In the blood stream, several proteolytic enzymes are known to occur. These include at least two leukoproteases which are capable of splitting native proteins largely to the proteose stage, and an erepsin-like enzyme freely hydrolyzing proteins from the intermediate stages (albumose and peptone) to the amino-acid forms. These enzymes seem to be derived from the disintegrating but not from living polymorphonuclear leukocytes, and fluctuations in the peripheral leukocyte count are not indicative of the relative titer of the enzyme concentration.1
Apart from leukocytes as the chief sources of proteolytic enzymes present in normal blood, small amounts of various digestive enzymes may be derived from gastro-intestinal tracts, the large abdominal organs and from areas altered pathologically if at all. They enter the blood stream possibly by way of the lymph current. These include a tryptase or protease, a polyvalent trypsin-like ferment capable of splitting native proteins all the way down to