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Physical Protein Regulation of Adenylate Kinases from Muscle, Liver, and Hepatoma¹

Department of Obstetrics and Gynecology, University of Florida College of Medicine, Gainesville, Florida 32610 [W. E. C., T. K. P.], and Department of Biochemistry, Howard University College of Medicine, Washington, D. C. 20001 [H. P. M.]

Homogenous preparations of the major adenylate kinases (EC 2.7.4.3) from rat liver, skeletal muscle, and Morris hepatoma 3924A have been compared by equilibrium ultracentrifugation, sodium dodecyl sulfate:polyacrylamide gel disc electrophoresis, amino acid analysis, and two-dimensional polypeptide mapping.

The hepatoma enzyme is composed of two polypeptide subunits of 13,000 daltons each and has a native molecular weight near 24,000 daltons. Liver adenylate kinase consists of two 13,000 dalton subunits and an 11,000 dalton subunit; the native form exists near 40,000 daltons. The muscle enzyme has four subunits at 13,000 daltons each. Its native form is near 50,000 daltons.

A unique polypeptide sequence in the liver adenylate kinase is also indicated from "fingerprint" and amino acid analysis.

It is probable that all three forms of adenylate kinase have subunits with similar size, but the liver form also has a unique smaller subunit that may be involved in its regulatability by citric acid-cycle metabolites. This unique polypeptide subunit is not present in the hepatoma enzyme. Therefore, if this latter polypeptide is produced from the derepression of a single structural gene, loss of the functioning of this gene in the tumor does not necessarily mean loss of enzymatic activity; it probably indicates a loss of metabolite regulatability of enzymatic activity.

¹ This research was supported by Grants CA-11818, CA-10729, and CA-10906 from the NIH and F73-UF4 from the Florida Division of the American Cancer Society.

² Recipient of NIH Research Career Development Award CA-70187.

Received 4/15/74. Accepted 8/ 2/74.