Re-characterisation of Saccharomyces cerevisiae Ach1p: Fungal CoA-transferases are involved in acetic acid detoxification

Saccharomyces cerevisiae and Neurospora crassa mutants defective in the so-called acetyl-CoA hydrolases Ach1p and Acu-8, respectively, display a severe growth defect on acetate, which is most strongly pronounced under acidic conditions. Acetyl-CoA hydrolysis is an energy wasting process and therefore denoted as a biochemical conundrum. Acetyl-CoA hydrolases show high sequence identity to the CoA-transferase CoaT from Aspergillus nidulans. Therefore, we extensively re-characterised the yeast enzyme. Ach1p showed highest specific activity for the CoASH transfer from succinyl-CoA to acetate and only a minor acetyl-CoA-hydrolase activity. Complementation of an ach1 mutant with the coaT gene reversed the growth defect on acetate confirming the in vivo function of Ach1p as a CoA-transferase. Our results imply that Ach1p is involved in mitochondrial acetate detoxification by a CoASH transfer from succinyl-CoA to acetate. Thereby, Ach1p does not perform the energy wasting hydrolysis of acetyl-CoA but conserves energy by the detoxification of mitochondrial acetate.