Studies on a protein isolated from livers of diabetic and fasted rats

A protein that is synthesized by livers of diabetic and fasting rats has been isolated and purified. This protein is either not synthesized or it is synthesized in trace amounts by livers of normal or fasted and refed animals. This component, designated as “7S” protein, accompanies the fatty acid synthetase through all steps of purification. However, it can be separated from the fatty acid synthetase by two successive sucrose density gradient centrifugations. When separated in this way it is nearly homogenous in size and charge (disk gel electrophoresis). The 7S proteins obtained from diabetic and fasted livers are identical with respect to size, charge, and immunochemical properties. This protein does not catalyze any of the partial reactions of fatty acid synthesis, does not bind acetyl or malonyl groups, and it does not exhibit acetyl-CoA carboxylase activity. Immunological studies show it to be unrelated to the fatty acid synthetase. Finally, it has no effect on the rate of fatty acid synthesis or on acetyl-CoA carboxylase activity. Thus, on the basis of these properties, the 7S protein is not related to the fatty acid synthetase and probably not to acetyl-CoA carboxylase. The function of this protein remains to be determined.