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Carboxypeptidases and Carboxypeptidase Inhibitor in Tumor-bearing Animals. A Possible Blood Test for Neoplasia^*

( U.S. Air Force Radiation Laboratory and Departments of Biochemistry and Pharmacology, University of Chicago, Chicago, Ill.)

The enzyme-inhibitor system consisting of carboxypeptidase a (requiring cysteine), carboxypeptidase b (inhibited by cysteine), and simultaneously occurring inhibitors (CPaI and CPbI) of these two enzymes has been studied in a variety of normal and tumor tissues and in the blood of normal and tumor-bearing animals. Five different solid tumors of the mouse and rat have been found to be completely devoid of both enzymes and of both inhibitors. Two ascitic tumors of the mouse have been found free of both inhibitors but have been found to have both enzymes in the precipitate and none in the supernatant of homogenates of the ascitic cells centrifuged at high-speed. Of ten different normal tissues tested, nine had both enzymes in the supernatant, eight had CPaI in the precipitate, and none had CPbI. The ascitic fluid is the only tissue or fluid in which we have detected appreciable amounts of CPbI, and this was noted only erratically.

In contrast to normal rat and rabbit blood cells, we have found the blood cells of tumor-bearing animals to be essentially free of CPaI. This is suggested as a possible test for the presence of neoplasia.

^* This study was supported by funds provided under contract AF-33(038)27353 with the USAF School of Aviation Medicine, Randolph Field, Texas.

Received 6/10/53.