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Subcellular Location of Phosphoenolpyruvate Carboxykinase in Hepatocytes from Fed and Starved Rats1

Neal W. Cornell, Vern L. Schramm*, Michael J. Kerich and Frances A. Emig*

Laboratory of Metabolism, National Institute on Alcohol Abuse and Alcoholism, 12501 Washington Ave., Rockville, MD 20852 * Department of Biochemistry, Temple University School of Medicine, Philadelphia, PA 19140

To evaluate published indications that about 25% of the gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (PEPCK), is located in mitochondria of adult rat liver, cell fractionations were conducted with hepatocytes isolated from rats that were fed ad libitum or starved for 2 days. Hepatocytes were exposed to digitonin for 10 s, and the released materials were separated from residual cell structures by centrifugation through a layer of brominated hydrocarbon. In addition to PEPCK, activities of 9 other enzymes were measured in the untreated cells and with good recovery in the two fractions obtained with digitonin treatment. By comparison with the release of marker enzymes for the cytosol and mitochondria, the subcellular distribution of PEPCK was determined. With cells from either fed or 2-day-starved rats, this enzyme was released exactly like lactate dehydrogenase and within 2–3% of phosphoglycerate kinase and pyruvate kinase. These results indicate that, even after induction by starvation, at least 97% of PEPCK activity is located in the cytosol of rat liver.

KEY WORDS: • phosphoenolpyruvate carboxykinase • rat liver • cytosol • mitochondria

1 Supported in part by grants AM 25551 and GM 21083 from the National Institutes of Health (to V. L. S.).

Manuscript received 4 September 1985. Revision accepted 3 February 1988.






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