Separation of two active forms (holo- a and holo- b) of pigeon liver fatty acid synthetase and their interconversion by phosphorylation and dephosphorylation

Apo-, holo- a- and holo- b-pigeon liver fatty acid synthetases 4 were separated by affinity gel chromatography under conditions identical to those used for the separation of apo and holo forms [Qureshi et al. (1975) Biochem. Biophys. Res. Commun. 64, 836-844], except that an additional elution step at a high salt concentration, pH 7.0, and room temperature was included. The interconversion of the two forms of holo-fatty acid synthetase was then carried out in vitro. In the presence of Mg ++ and a phosphatase preparation, holo- b was converted to holo- a. The reverse conversion, holo- a to holo- b, was carried out in the presence of ATP and a kinase fraction prepared from the 100, 000 g supernatant of liver homogenate. These results indicate that the interconversion of holo- a- and holo- b-fatty acid synthetases occurs by phosphorylation-dephosphorylation. These results also suggest the possibility that this process may be a mechanism of short term regulation of liver fatty acid synthetase activity.