Abstract
Pantothenate kinase catalyzes the rate-controlling step in the coenzyme A (CoA) biosynthetic pathway, and its activity is modulated by the size of the CoA pool. The effect of nonesterified CoA (CoASH) and CoA thioesters on the activity of pantothenate kinase was examined to determine which component of the CoA pool is the most effective regulator of the enzyme from Escherichia coli. CoASH was five times more potent than acetyl-CoA or other CoA thioesters as an inhibitor of pantothenate kinase activity in vitro. Inhibition by CoA thioesters was not due to their hydrolysis to CoASH. CoASH inhibition was competitive with respect to ATP, thus providing a mechanism to coordinate CoA production with the energy state of the cell. There were considerable differences in the size and composition of the CoA pool in cells grown on different carbon sources, and a carbon source shift experiment was used to test the inhibitory effect of the different CoA species in vivo. A shift from glucose to acetate as the carbon source resulted in an increase in the CoASH:acetyl-CoA ratio from 0.7 to 4.3. The alteration in the CoA pool composition was associated with the selective inhibition of pantothenate phosphorylation, consistent with CoASH being a more potent regulator of pantothenate kinase activity in vivo. These results demonstrate that CoA biosynthesis is regulated through feedback inhibition of pantothenate kinase primarily by the concentration of CoASH and secondarily by the size of the CoA thioester pool.
Highlights
Step in the coenzyme A (CoA) biosynthetic pathway, and its activity is modulated by the size of the CoA pool
The effect of nonesterified CoA (CoASH)and CoA thioesters on the activity of pantothenate kinase was examined to determine which component of the CoA pool is the most effective regulator of the enzyme from Escherichia coli
There were considerable differences in the size and compositionof the CoA pool in cellsgrown on different carbon sources, and a carbon source shift experiment was used to test the inhibitory effect of the different similar analysis of radiolabeled metabolites in the rat heart perfused with D-[l-’4C]pantothenate suggests that pantothenate phosphorylation is the primary regulatory site for
Summary
The altera- the regulation of pantothenate kinase in vivo are difficult to tion in the CoA pool composition was associated with assess in the animal studies due to the compartmentalization the selective inhibition of pantothenate phosphoryla- of CoAand the unknowcnomposition of the cytoplasmic CoA tion, consistent with CoASH being a more potent reg- thioester pool; the estimated total cytosolic CoA ulator of pantothenate kinase activity in vivo. These results demonstratethat CoA biosynthesis is regulated through feedback inhibition of pantothenate kinase primarily by the concentration of CoASH and secondarily by the size of the CoA thioester pool. Withitsthioesters,is a regulator of several key metabolic reactions such as pyruvatedehydrogenase and phosphoenol-
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