Studies of routes of energy losses from neoplastic cells continued using a model consisting of a control rat hepatocyte line and its N-nitroso-N-methlyureau-transformed counterpart. Studies of energy loss focused on the enzyme, lactic dehydrogenase (LDH, E.C. 1.1.1.27), because it is known to produce lactic acid in larger quantities in neoplastic cells and to export it into the medium, representing an energy loss. Eight subtypes of LDH were identified with isoelectric points between pH 5.96 and 9.46. Four acidic proteins below pH 7 are more prominent in LDH from the control cell and are believed to be phosphorylated proteins on the basis of previous results. In neoplastic cells, 35% of the glucose taken up for cell growth is converted to lactic acid, representing a sizeable loss of energy compared with the 8.5% converted to lactic acid by the control cell. Earlier studies of LDH behavior suggested this difference. Structural studies on cells grown on microspheres and on flat surfaces show the ability of the neoplasic cell to grow attached to a more limited surface area than the control cell, compared within the same time periods. Neoplastic cells continue to grow on the spherical surface, whereas control cells grow beyond the area and spread on the flat surface of the flask. Study of the cytoskeletal proteins, actin, cytokeratin and tubulin, showed that, whereas tubulin appears to be the same in both cell lines, cytokeratin is reduced and actin is markedly reduced in the neoplstic cell, especially in the region of the plasma membrane, suggesting that morphological changes in the membrane may relate to the loss of adequate cytoskeletal attachments.
