High malic enzyme activity in tumor cells and its cross-reaction with anti-pigeon liver malic enzyme serum.

Rabbit antibodies against pigeon liver malic enzyme (EC 1.1.1.40) were prepared. The antiserum gave single precipitation line with crude pigeon liver extract. Cross reaction was observed with partially purified malic enzyme or crude extract from chicken liver. Positive cross reaction was also observed with the concentrated cytosolic fraction of two human carcinoma cell lines which were demonstrated to contain high malic enzyme activity. All other proteins examined did not react with the antibodies. When purified pigeon liver malic enzyme was mixed with the antiserum in vitro, a time-dependent inactivation of the enzyme activity was observed. Protection of the enzyme activity against antiserum inactivation was afforded by NADP+ or L-malate. Metal Mn2+ gave little protection.