Lipid requirements for the structure and function of the fatty acid synthetase complex from Ceratitis capitata.

Abstract

Lipid content of purified fatty acid synthetase preparations from the Dipterous Ceratitis capitata correlated with the enzyme activity. Delipidation of the enzyme by extracting with a series of organic solvents rendered a protein without any residual activity and the treatment with phospholipase A2 for 30 min reduced the activity to 10%. Addition of lipid classes to either the native enzyme or the phospholipase-treated preparation enhanced the activity in a different manner, phosphatidylethanolamine being the most effective lipid. The role of the lipids in the lipoprotein structure of the complex was studied by circular dichroism spectra of the native enzyme and in the presence of a concentration range of urea, guanidinium chloride, sodium dodecyl sulfate, sodium cholate, and sodium chloride. 3 M urea and 1.5 M guanidinium chloride induced a conformational transition of the lipoprotein that lost its alpha-helical structure at higher concentrations of both reagents. Sodium dodecyl sulfate and sodium cholate had little effect on the alpha-helical structure, although both reagents induced the loss of enzyme activity. Cholate had essentially the same effect as phospholipids on the maintenance of the native structure but it was unable to support the enzyme activity.