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In vivo control of actin polymerization in sacoma-180 ascites tumor cells
Actin was isolated and purified from sarcoma-180 ascites tumor cells by a method employing DEAE-cellulose anion exchange chromatography, polymerization-depolymerization and exclusion chromatography. The actin was demonstrated to polymerize in an in vitro system. SDS-polyacrylamide gel electrophoresis was performed upon crude extracts of the sarcoma-180 cells and the total amount of actin was determined on a per cell basis. Thirteen percent of the total, and 12.6% of the soluble, protein of the sarcoma-180 cell was determined to be actin. This corresponds to an intracellular actin concentration of 6 mg/ml. These results are discussed in terms of current theories of in vivo control of tumor cell actin polymerization and microfilament assembly. The intracellular contents of the sarcoma-180 tumor cells were demonstrated to be very acidic by measuring the change in pH of a cell suspension before and after gentle lysis of the cells. This result, coupled with the experimental results on other tumor cells as reported in the literature, forms the basis for an alternative mechanism for the in vivo control of actin polymerization involving intracellular pH.