title: Fatty acid synthetase complex from the insect Ceratitis capitata. Structural studies.
abstract: 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.
mesh_terms: D000818:Animals; D002519:Ceratopogonidae / Q000201:enzymology*; D002918:Chymotrypsin / Q000378:metabolism; D002942:Circular Dichroism; D064429:Fatty Acid Synthases / Q000032:analysis*; D008066:Lipolysis; D046911:Macromolecular Substances; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D013696:Temperature; D013774:Tetranitromethane; D014357:Trypsin / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D064429:Fatty Acid Synthases; D010741:Phospholipases A; D054467:Phospholipases A2; D002918:Chymotrypsin; D014357:Trypsin; D013774:Tetranitromethane