Amphibian embryo protease inhibitor. III. Binding studies on the trypsin inhibitor and properties of its yolk-bound form.

Amphibian embryo trypsin inhibitor (ATI) is shown to be a temporary inhibitor in which full trypsin activity can eventually be restored. Lineweaver-Burk plots and other binding data indicate a reversible change from competitive to non-competitive inhibition during incubation of enzyme with inhibitor in the absence of substrate. The inhibitor is active while sequestered in the yolk, and the sequestered inhibitor co-purifies with lipovitellin when the yolk is fractionated. It is further demonstrated that the inhibitor slowly leaches from the yolk in a soluble form, and it is suggested that this leakage is the result of a negative feedback controlled proteolysis within the yolk. Possible interactions between ATI and endogenous trypsin-like proteases are discussed with particular regard to the potential involvement of those materials in the control of certain developmental events; notably melanogenesis.