The distinctiveness of ATP:citrate lyase from Aspergillus nidulans

ATP:citrate lyase (ACL), an important enzyme in lipid synthesis, has been purified from Aspergillus nidulans to a specific activity of 19.6 μmol min⁻¹ mg⁻¹, almost twice that of any other purified ACL and shown to be distinct from any previously purified ACL. The enzyme is a 371±31 kDa hexamer of 3α, 3β proteins, unlike the 4α tetramer found in rats or yeasts. The molecular weights of the α and β protein subunits were determined by SDS-PAGE to be 70 and 55 kDa.

ACL in A. nidulans (unlike Aspergillus niger) appears to be regulated by the carbon source present in the media. In crude extracts, it was found at high activity (88 μmol min⁻¹ mg protein⁻¹) in glucose-grown cells but only at low activity (10 μmol min⁻¹ mg protein⁻¹) in acetate-grown cells.