Studies on TI-2 trypsin inhibitor of Streptomyces griseus

The trypsin inhibitor TI-2 produced by Streptomyces griseus Cal in a medium, containing beef extract and peptone as the nitrogen source, was purified by ammonium sulfate precipitation and gel filtration. Amino acid analysis showed that it contained hydroxyproline and carbohydrate whereas tyrosine, tryptophan, and cystine were absent. The composition of the inhibitor protein thus showed a similarity to collagen. Growth of the organism in a medium with gelatin as the sole nitrogen source resulted in the production of the same TI-2 inhibitor. Incubation of gelatin with either concentrated culture filtrate, trypsin, or chymotrypsin also yielded trypsin inhibitors. The product isolated from the in vitro incubation of gelatin with trypsin appeared to be the same as TI-2. To the author's knowledge, this is the first report that peptides obtained by enzymic hydrolyses of gelatin are trypsin inhibitors.