Plasma membranes were isolated from normal rat livers, livers of rats fed for various periods of time with 4‐dimethylaminoazobenzene (4‐DAB), primary hepatomas, and transplants of hepatoma 484. The tissues were homogenized in three media, i.e. 1 mM HCO3 of pH 7.5, 1 mM NaHCO3 containing 2 mM CaCl2, and 2.8 mM citric acid. The isolated plasma membranes were assayed for enzymes previously demonstrated in plasma membranes isolated from rat‐liver homogenates prepared in 1 mM NaHCO3. Enzyme levels in liver membranes obtained from dilute citric acid homogenates differed markedly from those obtained following tissue homogenization in the bicarbonate media. The hepatoma‐484 membranes obtained from citric acid homogenates resembled enzymatically those isolated from bicarbonate‐CaCl2 medium. Of the three homogenization media employed, 1 mM NaHCO3‐2 mM CaCl2 (CaCl2 being required for the isolation of hepatoma‐484 membranes, but being optional for liver) yielded membranes most suitable for a comparative investigation. None of the enzymes present in liver membranes was absent from the hepatoma‐484 membranes. Hexokinase was present in the latter but absent from liver and primary‐hepatoma membranes. No difference in specific enzyme activities between liver and hepatoma‐484 membranes was observed for acid nitrophenylphosphatase, acetylphosphatase, K+‐acetylphosphatase, glucose‐6‐phosphatase and, as formerly shown, leucyl‐β‐naphthylamidase. Alkaline and acid glycerolphosphatases, alkaline nitrophenylphosphatase and alkaline K+‐nitrophenylphosphatase, alkaline and acid phosphodiesterases, and (Na±K+) ATPase were from slightly to markedly increased in the hepatoma as compared with liver membranes, The ATPase, 5′‐mononucleotidase, “neutral” nitrophenylphosphatase and “neutral” K+‐nitrophenylphosphatase, inosine diphosphatase and non‐specific esterase activities were lower in hepatoma than in liver membranes. Alkaline glycerolphosphatase and acid phosphodiesterase increased and ATPase and non‐specific esterase decreased in activity with the development of the neoplastic process to reach, respectively, the highest and the lowest levels in the membranes of the transplanted hepatoma. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company
