Increased nucleoside triphosphatase activity of rat liver nuclear matrix following low dose carcinogen intoxication

Rats were treated with low doses of hepatocarcinogens and nuclear matrix was isolated 48 hours later. These treatments, which were associated with notable nuclear enlargement, produced a decrease in the proportion of large molecular weight nuclear matrix polypeptides in all of the treated preparations, in the absence of toxic sequelae. We also found that the control matrix preparations possessed a considerable Mg-dependent nucleoside triphosphatase; the specific activity was 1.77 μmol γ-Pi released per hour per mg protein, and the Michaelis constant was 0.5 mM ATP. The matrix activity hydrolyzed ATP, UTP, and TTP, but differed from the nuclear envelope enzyme in that it did not hydrolyze GTP, CTP, dATP, or ADP, and it lacked myokinase-like activity. Large increases in nuclear matrix nucleoside triphosphatase occurred following all of the carcinogen treatments. The increased activity may relate to nuclear envelope alterations and derangements in RNA transport associated with carcinogenesis.