Dergunov A D, Shuvaev V V, Perova N V
Biochemistry Department, USSR Research Centre for Preventive Medicine, Moscow.
Biochim Biophys Acta. 1989 Sep 11;1005(1):79-86. doi: 10.1016/0005-2760(89)90034-9.
A lower accessibility to water-soluble quenchers of tryptophanyls of VLDL apolipoproteins B, E, C as compared to LDL apoB chromophores has been detected by a fluorescence quenching technique. The dynamic behaviour of the tryptophanyls of VLDL amphipathic apolipoproteins E and C did not change in the presence of a detergent, Tween-20, at sub-lytic concentrations. However, a reversible structural transition registered by the 'red' shift of the emission spectrum maximum and the changes in the quenching pattern by I- occurred under these conditions. The increase in the VLDL tryptophanyl accessibility to acrylamide and the decrease in the quenching constant were observed at partial and complete solubilization of the VLDL particles by the detergent. Dissociation of apolipoproteins from VLDL occurred after their treatment with Tween-20 or lipoprotein lipase isolated from bovine milk, and the tryptophanyl population not participating in fluorescence energy transfer on lipid phase-localized fluorescent probe pyrene appeared. In the presence of Tween-20, the relative affinity of apoE for the lipid matrix of VLDL was lower than that of apoC. Besides, the uncompetitive mode of inhibition of the LPL activity by apoC-III has been demonstrated. It is suggested that: (1) the amphipathic apolipoproteins E and C are organized as clusters on the VLDL surface and/or partially shielded by apolipoprotein B: (2) self-regulation of lypolysis may exist involving detergent-like reaction product accumulation and changes in relative apolipoprotein contents.
通过荧光猝灭技术检测发现，与低密度脂蛋白（LDL）载脂蛋白B发色团相比，极低密度脂蛋白（VLDL）载脂蛋白B、E、C中色氨酸残基对水溶性猝灭剂的可及性较低。在亚裂解浓度的去污剂吐温-20存在下，VLDL两亲性载脂蛋白E和C中色氨酸残基的动态行为未发生变化。然而，在此条件下，发射光谱最大波长的“红移”以及碘离子引起的猝灭模式变化记录到了可逆的结构转变。在用去污剂使VLDL颗粒部分或完全溶解时，观察到VLDL色氨酸残基对丙烯酰胺的可及性增加以及猝灭常数降低。用吐温-20或从牛乳中分离的脂蛋白脂肪酶处理VLDL后，载脂蛋白从VLDL上解离，出现了不参与脂质相定位荧光探针芘荧光能量转移的色氨酸残基群体。在吐温-20存在下，载脂蛋白E对VLDL脂质基质的相对亲和力低于载脂蛋白C。此外，已证明载脂蛋白C-III对脂蛋白脂肪酶（LPL）活性的抑制模式为非竞争性抑制。有人提出：（1）两亲性载脂蛋白E和C在VLDL表面以簇状形式组织存在和/或部分被载脂蛋白B屏蔽；（2）可能存在脂解的自我调节，涉及类似去污剂的反应产物积累以及载脂蛋白相对含量的变化。
