Utilization of a continuous flow reactor to study the lipoprotein-
associated coagulation inhibitor (LACI) that inhibits tissue factor
CH Gemmell, GJ Broze , VT Turitto and Y Nemerson
Department of Medicine, Mt Sinai Medical Center, New York, NY 10029.
A microperfusion system containing a glass capillary, the inner surface of
which is coated with a phospholipid bilayer containing tissue factor, was
used to explore the requirement for factors VIIa and Xa in the complex
formed with the lipoprotein-associated coagulation inhibitor (LACI).
Various combinations of factors VIIa, Xa, and LACI were perfused together
or sequentially at a wall shear rate of 300 sec- 1; a final perfusion of
factors X and VIIa was performed to evaluate the residual tissue factor
activity. Factor Xa concentration at the outlet of the tube was determined
using a chromogenic substrate. In the presence of factors VIIa, Xa, and
LACI, complete inhibition of tissue factor was observed on both
phosphatidylcholine (neutral surfaces) and on
phosphatidylserine/phosphatidylcholine (acidic) surfaces; omission of
factors Xa or LACI resulted in no inhibition. The absence of factor VIIa in
the initial perfusion steps resulted in no inhibition on neutral surfaces
whereas about 90% inhibition was observed on acidic surfaces. Initial
perfusion with factor Xa, but not LACI, followed by the remaining protein
components, resulted in an inhibitory complex. Thus, it appears that a
tissue factor:factor Xa:LACI complex can form in the absence of factor VIIa
on acidic surfaces; moreover, our data imply a tissue factor binding site
for factor Xa, but not for LACI.
Volume 76,
Issue 11,
pp. 2266-2271,
12/01/1990
Copyright © 1990 by The American Society of Hematology
