MATERIALS AND METHODS We have reported previously that a factor with a molecular weight of 53,000 under SDS-polyacrylamide gel electrophoresis purified from hu man erythrocyte extracts promoted the growth of a wide variety of cell

on July 21, 2017. © 1995 American Association for Cancer Research. cancerres.aacrjournals.org Downloaded from CATALASE AS A GROWTH.PROMOTING FACFOR with the primary amino acid sequences obtained from human catalase cDNA (Table 1). It was of note that the lysine residue, which is hydrolyzed by the lysyl endopeptidase, was found in just prior to the sequenced peptides. Catalase Activity of the PUrified Factor and the Growth promoting Activity of Catalases. Because of the sequence analysis, the purified factor was analyzed for catalase activity. On the basis of decomposing activity of hydrogen peroxide, the purified factor ap peared to have catalase activity (67,400 units/mg). We then deter mined the growth-promoting activity of other catalases. As shown in Fig. 2, commercially available catalases from human erythrocytes, Aspergillus niger, or bovine liver and recombinant rat liver catalase are all able to stimulate the growth of K562 cells. The purified factor also promoted the growth of the cells in a similar manner as the commercially available catalase from human erythrocytes and recom binant rat liver catalase (data not shown). Although the data were not shown, the catalases also stimulated the proliferation of other cell types. Adsorption of the Growth-promoting and Catalase Activities with Antibody against Human Catalase. In order to confirm whether the growth-promoting factor is catalase, the purified factor and other catalases were adsorbed with rabbit antibody against human catalase. As shown in Fig. 3, the growth-promoting activity as well as catalase activity (data not shown) was adsorbed with the antibody. In contrast, normal rabbit IgG did not adsorb them. Effect of an Inhibitor of Catalase on the Growth-promoting Activity in the PUrified Factor. In order to determine whether the growth-promoting activity is associated with catalase activity, the purified factor was treated with an irreversible catalase inhibitor aminotriazole, and then the growth-promoting activity was deter mined. As shown in Fig. 4, both the enzyme and the growth-promot ing activities were markedly inhibited. The inactivation rate of cata lase and growth-promoting activity was 98.6 and 98.8%, respectively.