Fibrin(ogen) degradation by a 24k-endopeptidase from a Chryseobacterium Sp.

Abstract

Summary A novel 24k-endopeptidase purified from the conditioned medium of a novel species of the Chryseobacterium genus, degraded purified fibrinogen and fibrin. At an enzyme/substrate ratio of 1/200 to 1/1000 rapid degradation of the human fibrinogen α-chain occurred and delayed degradation of the β-chain, whereas the γ-chain was more resistant. Degradation was associated with loss of thrombin-inducible coagulation. Incubation of 24k-endopeptidase (500 nM) in human plasma at 37°C for 3 h resulted in a decrease in fibrinogen to 38 ± 7% of baseline, and an increase of the thrombin time from 21 ± 1 to 52 ± 17 s. Other coagulation factors as well as plasminogen were not significantly affected. Fibrinogen digested with 24k-endopeptidase did not confer anticoagulant properties when added to human plasma.

In a buffer milieu,¹²⁵I-fibrin labelled matrix was lysed in a time- and concentration-dependent manner by 24k-endopeptidase. Purified¹²⁵I-labelled fibrin clots (65 μl) in a buffer milieu (500 μl) were also efficiently lysed, requiring 50 nM 24k-endopeptidase for 50% lysis in 1 h. The presence of a physiological fibrinogen concentration in this assay did not affect lysis. In contrast, no significant lysis of¹²⁵I-fibrin labelled plasma clots (65 μl) in human plasma (500 μl) was observed upon incubation with 24k-endopeptidase (up to 1 μM) for up to 24 h. Incubation of 24k-endopeptidase with α₂-macroglobulin resulted in formation of a complex with impaired proteolytic activity against fibrinogen. These findings indicate that 24k-endopeptidase may reduce plasma coagulability by degradation of fibrinogen and that its differential action on fibrin in a buffer milieu or in plasma may be due to inhibition by α₂-macroglobulin.