Partial activation of the factor VIIIa factor IXa enzyme complex by dihexanoic phosphatidylserine at submicellar concentrations

被引:14
作者
Gilbert, GE
Arena, AA
机构
[1] BRIGHAM & WOMENS HOSP, DEPT MED, BOSTON, MA 02115 USA
[2] HARVARD UNIV, SCH MED, DEPT MED, BOSTON, MA 02132 USA
关键词
D O I
10.1021/bi970537y
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Phosphatidylserine (PS)-containing membranes increase the k(cat) of the factor VIIIa-factor IXa enzyme complex by more than 1000-fold, While PS supports specific, high-affinity membrane binding of factor VIIIa and factor IXa, it is not known whether PS is the lipid that activates the membrane-bound complex. It is also not known whether PS or other activating lipids must reside in the two-dimensional membrane matrix for efficacy, We have found that submicellar concentrations of dihexanoic phosphatidylserine (C6PS) increase the activity of the factor Vma-factor IXa complex in a biphasic manner with half-maximal concentrations of 0.2 and 1.6 mM while the micelle-forming concentration is 4.0 mM, Increased cleavage of factor X at 0.25 mM C6PS was due to a 25-fold enhancement of the k(cat) and a 30-fold increase in the affinity of factor Vma for factor IXa, C6 phosphatidylethanolamine and C6 phosphatidic acid, but not C6 phosphatidylcholine, also accelerated the Xase complex, indicating that k(cat) enhancement has less structural specificity than membrane binding. Submicellar C6PS enhanced activity of factor IXa in the absence of factor VIIIa, but the effect was due to a decreased K-M rather than an increased k(cat), These results suggest that activation of the factor VIIIa-factor IXa complex can result from binding of individual C6PS molecules or small aggregates in the absence of a membrane bilayer. They provide a model system in which the phospholipid-induced activation may be distinguished from membrane-binding of the enzyme complex.
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页码:10768 / 10776
页数:9
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