The amino-acid sequences of the double-headed proteinase inhibitors from cat, lion and dog submandibular glands.

Cat and lion submandibular glands each contain a double-headed secretory proteinase inhibitor. Their amino-acid sequences were determined, and the amino-acid sequence of the inhibitor of dog submandibular glands was revised. Extensive homologies were found between these inhibitors in both domains. The trypsin-inhibiting domains of cat and lion inhibitors, however, contain a Lys residue in the reactive site in contrast to an Arg residue in the dog inhibitor. Domains I and II of cat, lion, and dog inhibitors are structurally related both to each other and to the sequenced monovalent secretory pancreatic trypsin inhibitors, Notable differences in inhibitory properties of canine and feline inhibitors are discussed with respect to sequence differences.