Glyoxylate cycle in Mucor racemosus.

The dimorphic phycomycete Mucor racemosus was grown in media containing acetate, glutamate, and peptone as carbon sources. The component enzymes of the glyoxylate bypass, isocitrate lyase and malate synthase, were present under these conditions throughout the growth cycles. Highest specific activities for each enzyme were found in media with acetate as the carbon source. In an enriched peptone medium containing glucose, neither activity was detected until glucose was exhausted from the medium. Treatment of acetate-grown cells with glucose resulted in a rapid decline in the specific activities of both enzymes. The importance of this cycle in acetate-grown cells was indicated by the ability of itaconic acid (100 mM) to inhibit the growth of M. racemosus in acetate but not glutamate media. Itaconate was also shown to be a potent inhibitor of isocitrate lyase activity in vitro.