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Extraction of a Factor from Ehrlich Ascites Tumor Cells That Increases the Activity of the Fetal Isozyme of Pyruvate Kinase in Mouse Liver¹

Department of Biological Chemistry, California College of Medicine, University of California, Irvine, Irvine, California 92664

Isoelectrofocusing studies of mouse tissue extracts show mice to have a pyruvate kinase isozyme pattern very similar to that of the rat. Moreover, electrofocusing or kinetic assays conducted on liver extracts from normal mice and from mice bearing Ehrlich ascites tumors show that the latter have a higher proportion of the fetal K-isozyme of pyruvate kinase. Serial injection of the supernatant remaining after centrifugation of homogenized tumor cells at 100,000 x g, or of the phenolic extracts from the latter, produced a similar shift in the liver isozyme pattern. This shift in the liver isozyme pattern involves both a decrease in L-isozyme activity and an increase in K-isozyme activity. However, only the increase in activity of the K-isozyme appears to be a specific response to injection of the extracts. The presence of a specific factor in these extracts was confirmed by the observation that similar extracts prepared from normal adult tissues did not increase activity of the K-isozyme. On the other hand, phenolic extracts from fetal mice did increase K-isozyme activity as did injections of serum from tumor-bearing mice or of the cell-free ascites fluid. Evidence is presented supporting the concept that the factor is proteinaceous in nature, and that it acts by derepressing synthesis of the K-isozyme.

¹ This work was supported by USPHS Grant CA-07883 and by a grant from the Dannebaum Fund via the College Research Committee.

² To whom reprint requests and correspondence should be addressed.

Received 7/ 8/74. Accepted 10/ 7/74.