Effect Of Neuraminidase On Plasmin Formation By Urokinase And The Vascular Plasminogen Activator
Thrombosis and Haemostasis
It was the aim of the present study to determine whether sialic acid residues in the activator or substrate molecule play a role in the activation of plaminogen to plasmin by the vascular plasminogen activator (VPA) and urokinase (UK).Using a purified test system with UK (Mr=31.000, human urine), VPA (Mr=70.000, cadaver vessel eluates) as activators, Glu-plasminogen as substrate, and pretreatment with neuraminidase (C.perfringens,1.51U/mg) it could be shown by quantification of the formed
... of the formed plasmin with S-2251 as substrate that neuraminidase treatment enhances plasmin formation by UK as well as by VPA. Using Sepharose-bound neuraminidase (C.perfringens, 20-30U/g Sepharose) it could be shown that neuraminidase affects the substrate in a dose and time dependent fashion, while the activity of the activators seems to remain unchanged. Treatment of plasminogen with neuraminidase in a concentration of 2.5 mU per μmole plasminogen for 90 min. at 37°C increased the plasmin formation by VPA by about 50% which was the same as for UK.Kinetic analysis of plasmin formation from neuraminidase treated plasminogen by UK and VPA suggests increased binding of the substrate to the activators (unchanged Vmax and decreased KM). The enhancing effect of fibrin on plasmin formation by VPA seems to remain unaltered by neuraminidase treatment of the plasminogen.These data suggest that, as in the case of other protease substrates, removal of sialic acid residues results in increased cleavage of the substrate, i.e. enhanced plasminogen activation, regardless of the type of activator.