Methylcitrate synthase is a key enzyme of the methylcitrate cycle and required for fungal propionate degradation. Propionate not only serves as a carbon source, but also acts as a food preservative (E280–283) and pos-sesses a negative effect on polyketide synthesis. To investigate propionate metabolism from the opportunistic human pathogenic fungusAspergillus fumigatus, methylcitrate synthase was purified to homogeneity and charac-terized.