Inhibitory mechanism of serpins. Interaction of thrombin with antithrombin and protease nexin 1.
The mechanism for the inhibition of thrombin by the serpins antithrombin and protease nexin 1 has been investigated using several kinetic techniques at pH 7.9 and 37 degrees C with an ionic strength of 0.3 M. Rapid kinetic studies demonstrated that a two-step mechanism for the formation of the stable thrombin-serpin complex applied to both serpins. The inhibition constant for the initial thrombin-antithrombin complex was 265 microM, and the rate constant for the conversion of this complex to the final one was 3.9 s-1; the corresponding values for PN1 were 3.4 microM and 6.0 s-1. By using slow-binding kinetics, it was possible to obtain estimates of the second-order rate constants for the formation of the stable thrombin-serpin complexes (1.2 x 10(4) and 1.5 x 10(6) M-1 s-1 for antithrombin and protease nexin 1, respectively) and the dissociation constants for these complexes (< 1 nM for both serpins). The influence of viscosity on the reactions indicated that the rate of interaction of both serpins with thrombin was diffusion-controlled. Moreover, the results indicated that the initial complex reacted more rapidly to form the stable complex than it dissociated to free enzyme and inhibitor; i.e., the behavior of the serpins was analogous to that of "sticky" substrates. By using the results from slow-binding, viscosity, and rapid kinetic studies, it was possible to set values for all of the rate constants for the interactions of antithrombin and protease nexin 1 with thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)
Stone
S R
SR
Department of Haematology, University of Cambridge, MRC Centre, U.K.
Hermans
J M
JM
D000595:Amino Acid Sequence; D016564:Amyloid beta-Protein Precursor; D000991:Antithrombins / Q000378:metabolism* / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008956:Models, Chemical; D008969:Molecular Sequence Data; D058255:Protease Nexins; D011485:Protein Binding; D011956:Receptors, Cell Surface; D015843:Serpins / Q000378:metabolism* / Q000494:pharmacology; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000378:metabolism*
D016564:Amyloid beta-Protein Precursor; D000991:Antithrombins; D002352:Carrier Proteins; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D015843:Serpins; D013917:Thrombin