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Expression of Multimolecular Forms of Pyruvate Kinase in Normal, Benign, and Malignant Human Breast Tissue¹

Department of Biological Chemistry, California College of Medicine, University of California, Irvine 92717 [K. H. I., K. N. G., A. M. H.], and Pathology Department, Whittier Hospital, Whittier 90605 [R. A. O., S. G., G. N.], California

The levels of multimolecular forms of pyruvate kinase present in four normal human breast specimens, nine benign tissues, and 13 malignant breast carcinomas were determined. The different enzymatic forms were separated by isoelectrofocusing, quantitated photometrically, and characterized further by kinetic studies using phosphoenolpyruvate as the variable substrate in the presence of different effectors. A correlation between specific activity and malignancy was found. The mean specific activities (±S.E.) of the normal, benign, and malignant tissues were: 0.078 ± 0.006, 0.36 ± 0.072, and 3.50 ± 0.696 IU/mg protein, respectively. A form of pyruvate kinase with an isoelectric point (pl) of 7.0 predominated in the breast tissues. The properties of this form were consistent with it being the K₄ isozyme, known to be widely distributed in mammalian tissues. Higher pl forms were also found. The M₄ isozyme, expressed by normal muscle and brain, has a pl value similar to the highest pl form found in the breast tissues. Therefore, the pl data alone suggest that the breast specimens also express some M-type subunits. This conclusion was not supported by the kinetic data. The higher pl forms are thought to be a posttranslationally modified K isozyme. Although this modified form is found in normal specimens, it seems more prevalent in neoplasms.

¹ This investigation was supported by University of California, Cancer Research Coordinating Committee Grants 79114 and 8014.

² To whom requests for reprints should be addressed.

Received 7/ 8/81. Accepted 12/ 3/81.

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