title: Fractal kinetic behavior of plasmin on the surface of fibrin meshwork.
abstract: Intravascular fibrin clots are resolved by plasmin acting at the interface of gel phasesubstrate and fluid-borne enzyme. The classic Michaelis.Menten kinetic scheme cannot describe satisfactorily this heterogeneous-phase proteolysis because it assumes homogeneous well-mixed conditions. A more suitable model for these spatial constraints,known as fractal kinetics, includes a time-dependence of the Michaelis coefficient Km(F) = Km0F (1+ t)h, where h is a fractal exponent of time, t. The aim of the present study was to build up and experimentally validate a mathematical model for surface-acting plasmin that can contribute to a better understanding of the factors that influence fibrinolytic rates. The kinetic model was fitted to turbidimetric data for fibrinolysis under various conditions. The model predicted Km0(F) = 1.98 μM and h = 0.25 for fibrin composed of thin fibers and Km0(F) = 5.01 μM and h = 0.16 for thick fibers in line with a slower macroscale lytic rate (due to a stronger clustering trend reflected in the h value) despite faster cleavage of individual thin fibers (seen as lower Km0(F) ). ε-Aminocaproic acid at 1 mM or 8 U/mL carboxypeptidase-B eliminated the time-dependence of Km F and increased the lysis rate suggesting a role of C-terminal lysines in the progressive clustering of plasmin. This fractal kinetic concept gained structural support from imaging techniques. Atomic force microscopy revealed significant changes in plasmin distribution on a patterned fibrinogen surface in line with the time-dependent clustering of fluorescent plasminogen in confocal laser microscopy. These data from complementary approaches support a mechanism for loss of plasmin activity resulting from C-terminal lysine-dependent redistribution of enzyme molecules on the fibrin surface.
authors.affiliation: Department of Medical Biochemistry, Semmelweis University , 1094 Budapest, Hungary.
authors.forename: Imre
authors.initials: I
authors.lastname: Varjú
authors.forename: Kiril
authors.initials: K
authors.lastname: Tenekedjiev
authors.forename: Zsófia
authors.initials: Z
authors.lastname: Keresztes
authors.forename: Andrea Edit
authors.initials: AE
authors.lastname: Pap
authors.forename: László
authors.initials: L
authors.lastname: Szabó
authors.forename: Craig
authors.initials: C
authors.lastname: Thelwell
authors.forename: Colin
authors.initials: C
authors.lastname: Longstaff
authors.forename: Raymund
authors.initials: R
authors.lastname: Machovich
authors.forename: Krasimir
authors.initials: K
authors.lastname: Kolev
mesh_terms: D015119:Aminocaproic Acid / Q000737:chemistry; D043424:Carboxypeptidase B / Q000737:chemistry; D005337:Fibrin / Q000737:chemistry* / Q000648:ultrastructure; D005341:Fibrinolysin / Q000737:chemistry* / Q000648:ultrastructure; D017709:Fractals; D006801:Humans; D007700:Kinetics; D008956:Models, Chemical; D055503:Protein Multimerization; D059748:Proteolysis
chemical_list: D005337:Fibrin; D043424:Carboxypeptidase B; D005341:Fibrinolysin; D015119:Aminocaproic Acid