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The Uptake of Labeled Proteins by Particulate Fractions of Tumor and Normal Tissues after Injection into Mice¹

( Division of Neurological Surgery, Baltimore City Hospitals, and The Johns Hopkins University School of Medicine, Baltimore, Maryland)

The distribution of radioactivity among particulate fractions of tumor, liver, and kidney was examined after injection of arsonoazoalbumin-⁷⁴As in mice bearing the Zimmerman ependymoblastoma. In all tissues, the percentage of total activity in the particulate fraction at 900 x g (10 min) increased with time. In the liver, the radioactivity in the fraction at 39,000 x g (1 hr) was high during the first few min after injection and decreased to a constant level after 1 hr. In the kidney, the percentage of total radioactivity in the fraction at 39,000 x g was higher during the first 10 min after injection but did not reach the levels noted in the liver. In the tumor, radioactivity in the small particles remained consistently low throughout the course of the experiment. In all tissues, the radioactivity in the supernatant fraction tended to decrease with time.

The results suggest that the tumor used in this study removed protein from the circulation by a process similar to that of the liver and kidney, where pinocytosis vesicles are incorporated into lysosomes. Pinocytosis vesicles (particles at 39,000 x g) containing the injected material did not accumulate in the tumor immediately after injection perhaps because this tissue normally takes up protein from the circulation. Pinocytosis is not stimulated by the presence of altered protein as in the liver and kidney.

¹ Supported by contract AT (30-1) 2182, U. S. Atomic Energy Commission, and grant C-3265, National Cancer Institute, USPHS.

Received 1/11/65.