AN ISOPEPTIDE BOND SPLITTING ENZYME FROM HIRUDO MEDICINALIS SIMILAR TO GAMMA -GLUTAMYL TRANSPEPTIDASE

Destabilase is a new enzyme from Hirudo medicinalis and is probably involved in fibrinolysis. It has been purified and sequenced. The enzyme is able to split Glu Lys(N 6 -a-glutamyllysine) isopeptide bonds (bonds between the Â-amino group of lysine and the a-carboxylic group of glutamic acid). The biological function of this enzyme is the hydrolysis of factor XIIIa crosslinked clots [1]. The enzyme is found in the saliva of Hirudo medicinalis and has a molecular mass of 12 300 Da [2, 3]. The protein consists of 115 amino acids, is rich in cystein residues and possibly modified at a threonine residue. It has no similarity to any protein known in the databases. Several different isoforms have been cloned. Crosslinking by factor XIIIa is a severe barrier to the dissolution of aged fibrin clots by the tissue plasminogen activator. Therefore, we tried to identify further proteins from the medical leech possibly involved in the dissolution of fibrin clots.