Gavilanes J G, Lizarbe M A, Municio A M, Oñaderra M
Biochim Biophys Acta. 1981 Apr 28;668(2):246-56. doi: 10.1016/0005-2795(81)90032-5.
The involvement of lipids in the structure and the activity of the fatty acid synthetase from the insect Ceratitis capitata has been previously established. Lipid-protein interactions were examined by circular dichroism. A thermal transition for both the structure and the activity of the enzyme complex takes place at about 50 degrees C; as the temperature is raised alpha-helix content decreases considerably and, concomitantly, the enzyme undergoes a marked inactivation. After 180 min at 37 degrees C, the secondary structure of the enzyme complex is 20% alpha-helix, 33% beta structure and 47% of not ordered structure against 43%, 26% and 31% as respective percentages for the native form of the complex. Lipolytic digestion of the complex was carried out with either lipase or phospholipase A2 or a mixture of both enzymes. Any of the lipolytic treatments induces a decrease of [theta]220 and the simultaneous digestion with lipase plus phospholipase during 90 min account for a limit structure with 8% of alpha-helix. The secondary structure of the complex after treatment with proteolytic enzymes, trypsin or chymotrypsin, had 15% alpha-helix, 20% beta structure and 57% of not ordered structure. The preservation of the alpha-helix content indicates that lipids protect certain of the bonds cleavable in the absence of lipids. The structural organization of the complex was studied through sequences of lipolytic and proteolytic treatments; final organization was dependent on the initial lipolytic digestion in agreement with the peptide bond shielding by the lipid component. Nitration of the complex with tetranitromethane modified almost completely all tyrosine residues of the polypeptide chains.
先前已经证实脂质参与了地中海实蝇脂肪酸合成酶的结构和活性。通过圆二色性研究了脂蛋白相互作用。酶复合物的结构和活性在约50℃时发生热转变；随着温度升高，α-螺旋含量显著降低，同时酶发生明显失活。在37℃下180分钟后，酶复合物的二级结构为20%的α-螺旋、33%的β结构和47%的无序结构，而复合物天然形式的相应百分比分别为43%、26%和31%。用脂肪酶或磷脂酶A2或两种酶的混合物对复合物进行脂解消化。任何一种脂解处理都会导致[θ]220降低，在90分钟内用脂肪酶加磷脂酶同时消化会产生一种具有8%α-螺旋的极限结构。用蛋白水解酶胰蛋白酶或糜蛋白酶处理后，复合物的二级结构为15%的α-螺旋、20%的β结构和57%的无序结构。α-螺旋含量的保留表明脂质保护了某些在无脂质时可裂解的键。通过脂解和蛋白水解处理序列研究了复合物的结构组织；最终组织取决于初始脂解消化，这与脂质成分对肽键的屏蔽作用一致。用四硝基甲烷对复合物进行硝化几乎完全修饰了多肽链的所有酪氨酸残基。
