Neuenschwander P F, Bianco-Fisher E, Rezaie A R, Morrissey J H
Cardiovascular Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City 73104, USA.
Biochemistry. 1995 Oct 31;34(43):13988-93. doi: 10.1021/bi00043a004.
The effect of phosphatidylethanolamine (PE) on the activity of the factor VIIa-tissue factor complex (fVIIa-TF) has been examined with respect to plasma clotting activity and activation of factor X (fX) in a purified system. Vesicles prepared by relipidating membrane-anchored TF (dcTF; TF1-244, lacking the C-terminal cytoplasmic tail) into phospholipid vesicles containing 6 mol % phosphatidylserine (PS) and increasing levels of PE up to 40 mol % (the balance consisting of phosphatidylcholine) were found to progressively shorten TF-initiated clotting in normal human plasma to levels comparable to those observed using dcTF relipidated with cephalin. The shortened clotting times were at least in part due to the ability of PE-containing membranes to better support the activation of fX by the fVIIa.TF complex, as vesicles with increased PE content yielded progressively higher initial rates of fX activation. Surprisingly, PE substantially altered the sensitivity of fX activation to low levels of PS, yielding near-maximal rates of activation at only 3 mol % PS compared to 15-20 mol % PS required in the absence of PE. The effect of PE was not synergistic with that of PS since PE did not increase fX activation rates at high levels of PS (20 mol %). Examination of the kinetic parameters for fX activation revealed that the majority of the effect of PE was in decreasing the apparent Km for fX.(ABSTRACT TRUNCATED AT 250 WORDS)
在一个纯化系统中，针对血浆凝血活性和因子X（fX）的激活，研究了磷脂酰乙醇胺（PE）对因子VIIa-组织因子复合物（fVIIa-TF）活性的影响。通过将膜锚定组织因子（dcTF；TF1-244，缺少C末端细胞质尾巴）重新脂质化到含有6摩尔%磷脂酰丝氨酸（PS）且PE水平逐渐增加至40摩尔%（其余为磷脂酰胆碱）的磷脂囊泡中所制备的囊泡，被发现可使正常人血浆中由TF引发的凝血逐渐缩短至与使用脑磷脂重新脂质化的dcTF所观察到的水平相当。凝血时间缩短至少部分归因于含PE的膜能够更好地支持fVIIa.TF复合物对fX的激活，因为PE含量增加的囊泡产生了逐渐升高的fX激活初始速率。令人惊讶的是，PE显著改变了fX激活对低水平PS的敏感性，在仅3摩尔%PS时就能产生接近最大激活速率，而在没有PE的情况下需要15 - 20摩尔%PS。PE的作用与PS并非协同作用，因为在高水平PS（20摩尔%）时PE并未增加fX激活速率。对fX激活动力学参数的研究表明，PE的大部分作用在于降低fX的表观Km。（摘要截断于250字）
