Organization of citric acid cycle enzymes into a multienzyme cluster

The possibility that some of the enzymes of the citric acid cycle may be loosely associated into a multienzyme cluster has been investigated using extracts prepared by gentle disruption of cells. Gel filtration and sucrose density gradient centrifugation have shown that five sequential enzymes of the cycle specifically associate into a cluster: fumarase, malate dehydrogenase, citrate synthase, aconitase and isocitrate dehydrogenase. Ultrasonication destroys the abilities of the enzymes to associate. The cluster could catalyse the sequence of reactions leading from fumarate to oxoglutarate and has been found in extracts of several bacterial species as well as rat liver mitochondria.