The identification and estimation of elastase in serum and plasma.

1. Electrophoretic separation of partially purified elastase preparations from pancreas followed by incubation of the electrophoretogram in contact with an agar gel containing 4% of either Congo Red-stained or unstained elastin demonstrated that the enzyme which dissolves elastin can be identified with that which releases dye from the stained preparation. 2. A method for the estimation of elastase based on the release of dye from Congo Red-stained elastin is described. It is 23 times as sensitive as methods employing protein determination. 3. With the method, elastase activity can be identified in plasma and in a partially fractionated plasma protein preparation. 4. Lineweaver-Burk plots of these estimates of activity at a variety of substrate concentrations indicate that the reaction between elastase and the dyed elastin is more closely similar to that between elastase and the soluble substrate elastin rather than to that between elastase and the solid substrate. 5. Values for K(m) and V(max.) calculated for the enzyme present in plasma present further evidence for its identity with the pancreatic enzyme. 6. By calculation of the slopes of the Lineweaver-Burk plots for various enzyme concentrations it has proved possible to demonstrate that the inhibitor which is also present in the plasma is without effect on the enzyme when it acts on the dyed substrate.