[Destabilase: an enzyme of medicinal leech salivary gland secretion hydrolyzes the isopeptide bonds in stabilized fibrin].

The salivary gland secretion of the leech Hirudo medicinalis contains an enzyme termed by us as destabilase, which hydrolyzes the epsilon-(gamma-glutamyl)-lysine bonds as a result of fibrin stabilization by factor XIIIa in the presence of Ca2+. This hydrolysis, apart from the original lysine and glutamine, is characterized by an appearance of lysine and glutamic acid residues. The accumulation of glutamic acid residues leads to spontaneous depolymerization of the destabilized fibrin. As a result, fluid "spots" of destabilized fibrin depolymerization (DFD) begin to appear at the sites of leech secretion application on the surface of stabilized fibrin plates. The DFD activity of the leech salivary gland secretion manifests itself only in case of stabilized fibrin and increases with an increase in the stabilization degree. Treatment of leech secretion with diisopropylfluorophosphate does not affect the enzyme activity, which is completely blocked by monoiodoacetate. The mechanism of action of leech salivary gland secretion and the enzyme isolated from it, i. e., destabilase, was studied, using a synthetic chromogenic substrate - p-nitroanilide-gamma-glutamic acid. The amidolytic activity of leech salivary gland secretion is 2.2 +/- 0.18 nkat/ml, Km(app) for destabilase is 0.6 X 10(-5) M, V = 5.4 X 10(-3) mol/min.