Lactoferrin and transferrin fragments react with nitrite to form an inhibitor of Bacillus cereus spore outgrowth.

Tryptone is a pancreatic digest of casein which contains a heterogeneous mixture of substances that react with nitrite when heated in the presence of sodium thioglycolate to form a bacteriostatic agent which inhibits outgrowth of Bacillus cereus T spores. The substances which are precursors to the bacteriostatic agent can be fractionated on the basis of molecular size and charge and have properties which indicate that they are fragments of lactoferrin, an iron-binding glycoprotein. The bacteriostatic agent could also be formed directly from purified lactoferrin after it had been subjected to proteolysis. Transferrin, an analogous iron-binding protein found in animal serum, also showed these same properties. This system may be a useful model for studies of the mechanism and site of nitrite bacteriostatic action.