Singh T K, Ryan R O
Lipid and Lipoprotein Research Group University of Alberta, Edmonton, Canada.
Arch Biochem Biophys. 1991 May 1;286(2):376-82. doi: 10.1016/0003-9861(91)90054-m.
Following injection of [1-14C]acetate into the sphinx moth, Manduca sexta, radiolabel was incorporated into lipid components of the major hemolymph lipoprotein, adult high density lipophorin (HDLp-A). Analysis of the labeled lipids by thin layer chromatography and radiochromatogram scanning revealed incorporation of radioactivity into the diacylglycerol (DAG) and hydrocarbon components as well as a third lipid fraction of unknown identity. Lipid transfer experiments were carried out using 14C-lipid HDLp-A and human low density lipoprotein (LDL) as donor/acceptor substrates and M. sexta lipid transfer particle (LTP) as catalyst. In control incubations lacking LTP, nearly all of the radiolabeled lipid remained associated with HDLp-A. LTP, however, induced a time-dependent vectorial transfer of radiolabeled lipid from HDLp-A to LDL. Lipid analysis of the LDL fraction, reisolated following the transfer reaction, revealed that labeled lipid components originally associated with HDLp-A were present in the acceptor LDL particles. The recovery of radiolabeled hydrocarbon associated with LDL demonstrates the capacity of LTP to facilitate transfer of these long chain, extremely hydrophobic, lipids and suggests LTP may function as a mediator of hydrocarbon transport and metabolism in vivo. When acceptor LDL particles were analyzed prior to complete transfer of HDLp-A-associated lipid it was observed that DAG was transferred preferentially during the initial stages of the reaction after which hydrocarbon transfer increased. This result suggests that LTP may have a lipid substrate preference for DAG versus hydrocarbon. Alternatively the observed preference for DAG may be a function of the relative accessibility of the substrates within the donor lipoprotein. In other experiments it was demonstrated that, unlike other lipids associated with HDLp-A, free fatty acid spontaneously transfers to LDL in the absence of lipid transfer catalyst.
将[1-14C]乙酸盐注射到烟草天蛾（Manduca sexta）体内后，放射性标记被整合到主要血淋巴脂蛋白即成年高密度脂蛋白（HDLp-A）的脂质成分中。通过薄层色谱法和放射色谱扫描对标记脂质进行分析，结果显示放射性被整合到二酰甘油（DAG）和烃类成分以及一种身份不明的第三脂质组分中。使用14C标记脂质的HDLp-A和人低密度脂蛋白（LDL）作为供体/受体底物，并以烟草天蛾脂质转运颗粒（LTP）作为催化剂进行脂质转移实验。在缺乏LTP的对照孵育中，几乎所有放射性标记脂质都与HDLp-A结合。然而，LTP诱导了放射性标记脂质从HDLp-A到LDL的时间依赖性矢量转移。对转移反应后重新分离的LDL组分进行脂质分析，结果显示最初与HDLp-A相关的标记脂质成分存在于受体LDL颗粒中。与LDL相关的放射性标记烃类的回收证明了LTP促进这些长链、极疏水脂质转移的能力，并表明LTP可能在体内作为烃类运输和代谢的介质发挥作用。当在HDLp-A相关脂质完全转移之前分析受体LDL颗粒时，观察到在反应初始阶段DAG优先转移，之后烃类转移增加。这一结果表明，LTP对DAG与烃类可能存在脂质底物偏好。或者，观察到的对DAG的偏好可能是供体脂蛋白中底物相对可及性的函数。在其他实验中证明，与HDLp-A相关的其他脂质不同，游离脂肪酸在没有脂质转移催化剂的情况下会自发转移到LDL中。
