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Acetoacetate Coenzyme A Transferase Activity in Rat Hepatomas¹

Department of Physiological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 [A. F., K. W.], and The Department of Biochemistry, Howard University School of Medicine, Washington, D. C. 20059 [H. P. M.]

The presence of succinyl-coenzyme A:acetoacetate CoA transferase (CoA transferase) (EC 2.8.3.5), an initiator of ketone body utilization in nonhepatic tissue, was examined in liver from normal, partly hepatectomized, neonatal, and tumor-bearing rats, as well as in a series of transplantable rate hepatomas ranging widely in growth rate. While levels of CoA transferase are extremely low in normal, host, and regenerating liver, considerable amounts of activity are detectable in neonatal liver and in the hepatomas. In fact, the content of CoA transferase in the series of Morris hepatomas increases progressively with increase in tumorgrowth rate. The fastest-growing tumor studied (7288Ctc) contains about the same amount of CoA transferase activity as rat skeletal muscle (i.e., an activity of about 0.1 µmole of acetoacetate used per min per g tissue). These results clearly indicate that the faster-growing hepatomas have adequate capacity to utilize ketone bodies in bioenergetic or biosynthetic activities. Furthermore, the enzymes from normal and hepatoma 7288Ctc tissues are quite similar with respect to (a) size of about 10⁵ daltons, (b) reaction mechanism requiring formation of an enzyme:CoA intermediate (from ping-pong kinetic data), and (c) various kinetic parameters (such as Michaelis constants, product competitive inhibition constants, and acetoacetate substrate inhibition). The enzymes from rat skeletal muscle and Morris hepatoma 7288Ctc have the same isoelectric point (7.6), which differs from that for the rat heart enzyme (6.8).

¹ This work was supported by Grant BC-141 from the American Cancer Society and Grant CA 10729 from USPHS, National Cancer Institute.

² Research Career Development Awardee, USPHS, National Institute of General Medical Sciences (GM 70423). To whom requests for reprints should be addressed.

Received 1/10/75. Accepted 5/13/75.