Bisgaier C L, Sachdev O P, Lee E S, Williams K J, Blum C B, Glickman R M
J Lipid Res. 1987 Jun;28(6):693-703.
The effect of cholesterol esterification on the distribution of apoA-IV in human plasma was investigated. Human plasma was incubated in the presence or absence of the lecithin:cholesterol acyltransferase (LCAT) inhibitor 5,5-dithiobis(2-nitrobenzoic acid) (DTNB) and immediately fractionated by 6% agarose column chromatography. Fractions were monitored for apoA-IV, apoE, and apoA-I by radioimmunoassay (RIA). Incubation resulted in an elevated plasma concentration of cholesteryl ester and in an altered distribution of apoA-IV. After incubation apoA-IV eluted in the ordinarily apoA-IV-poor fractions of plasma that contain small VLDL particles, LDL, and HDL2. Inclusion of DTNB during the incubation resulted in some enlargement of HDL; however, both cholesterol esterification and lipoprotein binding of apoA-IV were inhibited. Addition of DTNB to plasma after incubation and prior to gel filtration had no effect on the apoA-IV distribution when the lipoproteins were immediately fractionated. Fasting plasma apoE was distributed in two or three peaks; in some plasmas there was a small peak that eluted with the column void volume, and, in all plasmas, there were larger peaks that eluted with the VLDL-LDL region and HDL2. Incubation resulted in displacement of HDL apoE to larger lipoproteins and this effect was observed in the presence or absence of DTNB. ApoA-I was distributed in a single broad peak that eluted in the region of HDL and the gel-filtered distribution was unaffected by incubation either in the presence or absence of DTNB. Incubation of plasma that was previously heated to 56 degrees C to inactivate LCAT resulted in no additional movement of apoA-IV onto lipoproteins, unless purified LCAT was present during incubation. The addition of heat-inactivated LCAT to the incubation, had no effect on movement of apoA-IV. These data suggest that human apoA-IV redistribution from the lipoprotein-free fraction to lipoprotein particles appears to be dependent on LCAT action. The mechanism responsible for the increased binding of apoA-IV to the surface of lipoproteins when LCAT acts may involve the generation of "gaps" in the lipoprotein surface due to the consumption of substrate from the surface and additional enlargement of the core. ApoA-IV may bind to these "gaps," where the packing density of the phospholipid head groups is reduced.
研究了胆固醇酯化对人血浆中载脂蛋白A-IV（apoA-IV）分布的影响。将人血浆在存在或不存在卵磷脂：胆固醇酰基转移酶（LCAT）抑制剂5,5-二硫代双（2-硝基苯甲酸）（DTNB）的情况下进行孵育，然后立即通过6%琼脂糖柱色谱进行分离。通过放射免疫测定法（RIA）监测各组分中的apoA-IV、载脂蛋白E（apoE）和载脂蛋白A-I（apoA-I）。孵育导致血浆中胆固醇酯浓度升高以及apoA-IV分布改变。孵育后，apoA-IV在通常含小极低密度脂蛋白（VLDL）颗粒、低密度脂蛋白（LDL）和高密度脂蛋白2（HDL2）的apoA-IV含量较低的血浆组分中洗脱。孵育过程中加入DTNB导致HDL有一定程度的增大；然而，胆固醇酯化和apoA-IV与脂蛋白的结合均受到抑制。孵育后且在凝胶过滤之前向血浆中加入DTNB，当脂蛋白立即进行分离时，对apoA-IV的分布没有影响。空腹血浆中的apoE分布在两个或三个峰中；在一些血浆中，有一个小峰在柱空体积处洗脱，并且在所有血浆中，有较大的峰在VLDL-LDL区域和HDL2处洗脱。孵育导致HDL中的apoE转移至较大的脂蛋白上，并且在存在或不存在DTNB的情况下均观察到这种效应。apoA-I分布在一个单一的宽峰中，在HDL区域洗脱，并且凝胶过滤后的分布不受孵育（无论是否存在DTNB）的影响。将先前加热至56℃以灭活LCAT的血浆进行孵育，除非孵育过程中存在纯化的LCAT，否则不会导致apoA-IV向脂蛋白上有额外的转移。向孵育体系中加入热灭活的LCAT，对apoA-IV的转移没有影响。这些数据表明，人apoA-IV从无脂蛋白组分重新分布至脂蛋白颗粒似乎依赖于LCAT的作用。当LCAT起作用时，apoA-IV与脂蛋白表面结合增加的机制可能涉及由于脂蛋白表面底物的消耗导致脂蛋白表面产生“间隙”以及核心进一步增大。apoA-IV可能结合至这些“间隙”，此处磷脂头部基团的堆积密度降低。
