Van der Horst D J, Van Doorn J M, Voshol H, Kanost M R, Ziegler R, Beenakkers A M
Department of Experimental Zoology, University of Utrecht, The Netherlands.
Eur J Biochem. 1991 Mar 14;196(2):509-17. doi: 10.1111/j.1432-1033.1991.tb15843.x.
Insects transport lipid for flight in the form of diacylglycerol-rich low-density lipoproteins (low-density lipophorin, LDLp), which in the hemolymph are produced from high-density lipophorin (HDLp) by reversible association with several molecules of an apolipoprotein, apolipophorin III (apoLp-III, Mr approximately 18,000-20,000) during lipid loading. Two isoforms of apoLp-III (a and b) were purified both from adult Locusta migratoria migratorioides hemolymph and LDLp, which have identical apparent Mr but differ in amino acid composition, NH2-terminal amino acid sequence, and isoelectric points (5.35 +/- 0.01 for apoLp-IIIa, 5.10 +/- 0.01 for apoLp-IIIb). The NH2-terminal sequence of apoLp-IIIb is identical to the primary structure of apoLp-III deduced from cloned cDNA [Kanost et al. (1988) J. Biol. Chem. 263, 10,568-10,573], whereas the NH2-terminal sequence of apoLp-IIIa is identical to that of apoLp-IIIb but preceded by Arg-Pro-, which is the C-terminal of the putative signal peptide coded by cDNA upstream from that coding for apoLp-IIIb. The ratio apoLp-IIIa apoLp-IIIb free in hemolymph is identical to that in LDLp (5:9); since 14 molecules of apoLp-III appear to be bound in one molecule of LDLp, an average of 5 molecules of apoLp-IIIa and 9 of apoLp-IIIb are involved in formation of each LDLp particle. In vivo studies using 35S-labeled apoLp-IIIa and b demonstrate that each of the isoforms can associate with HDLp to produce LDLp reversibly; in an in vitro system, production of LDLp containing exclusively apoLp-IIIa or apoLp-IIIb demonstrates independent participation of each isoform in LDLp formation.
昆虫以富含二酰甘油的低密度脂蛋白（低密度脂蛋白运载蛋白，LDLp）的形式运输用于飞行的脂质，在血淋巴中，低密度脂蛋白运载蛋白是在脂质装载过程中通过与几个载脂蛋白分子（载脂蛋白III，apoLp-III，分子量约为18,000 - 20,000）可逆结合，由高密度脂蛋白运载蛋白（HDLp）产生的。从成年非洲沙漠蝗血淋巴和LDLp中纯化出了两种apoLp-III同工型（a和b），它们具有相同的表观分子量，但氨基酸组成、NH2末端氨基酸序列和等电点不同（apoLp-IIIa为5.35±0.01，apoLp-IIIb为5.10±0.01）。apoLp-IIIb的NH2末端序列与从克隆的cDNA推导的apoLp-III一级结构相同[卡诺斯特等人（1988年）《生物化学杂志》263卷，10568 - 10573页]，而apoLp-IIIa的NH2末端序列与apoLp-IIIb相同，但前面有Arg-Pro-，这是由apoLp-IIIb编码上游的cDNA编码的假定信号肽的C末端。血淋巴中游离的apoLp-IIIa与apoLp-IIIb的比例与LDLp中的相同（5:9）；由于一个LDLp分子中似乎结合了14个apoLp-III分子，所以每个LDLp颗粒的形成平均涉及5个apoLp-IIIa分子和9个apoLp-IIIb分子。使用35S标记的apoLp-IIIa和b进行的体内研究表明，每种同工型都可以与HDLp可逆结合产生LDLp；在体外系统中，仅含有apoLp-IIIa或apoLp-IIIb的LDLp的产生证明了每种同工型在LDLp形成中的独立参与。
