Abstract
Trace amounts of dog trypsin mixed with dog serum or injected i.v. into the dog were bound mainly to the a-macroglobulins (82 per cent) and to α1-antitrypsin (18 per cent). The relative affinity of dog trypsin for the α-macroglobulins was about 30 times as high as for the other inhibitors taken together. Dog trypsin bound to α1-antitrypsin was rapidly taken over by the α-macroglobulins in vitro as well as in vivo. The trypsin-α-macroglobulin complexes injected i.v. or formed in vivo were rapidly eliminated from the blood stream following a first order reaction, while α1-antitrypsin-bound trypsin disappeared much slower as found for bovine trypsin and dog plasma trypsin inhibitors.