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J. Biochem, 1982, Vol. 91, No. 4 1363-1372
© 1982 Japanese Biochemical Society

research-article

Changes in Myosin during Differentiation of Myeloid Leukemia Cells1

Junji SAGARA, Kazuhiro NAGATA and Yasuo ICHIKAWA

Department of Cytochemistry, Chest Disease Research Institute, Kyoto University Sakyo-ku, Kyoto, Kyoto 606

Changes in cellular myosin were followed during the differentiation into macro-phages of a myeloid leukemia cell line (Ml) which can be induced by conditioned medium (CM) from a rat embryo culture. To extract the myosin, we used three different procedures, all of which gave a lower yield of myosin for the differentiated than for the undifferentiated Ml cells. This low extractability we attributed to increased binding of the myosin to the plasma membrane. Taking the different extractabilities into consideration, we calculated the myosin contents in the total cellular protein from the densitometry of SDS-polyacrylamide electrophoresis, 0.6% for the untreated Ml cells and 1.0% for the differentiated ones. The three ATPase activities of the Ml cell myosin were in the order, K+-EDTA-=Ca2+–»Mg2+-ATPase in the presence of 0.6 M KCl, whether or not there was treatment with CM. Myosin was purified through fractionation with 25–55% saturated ammonium sulfate, then gel filtration with Sepharose 4B followed by affinity chromatography on F actin-Sepharose 4B. The Ml cell myosin consists of 1 heavy chain (H) and 3 light chains (L1, L2, L3), with molecular ratios of L1+L2/H=1. The ratio of L1/L2 was about 1.2 for the untreated Ml cells, but it decreased to about 0.7 after differentiation.

1This study was supported by a Grant-in-Aid for Cancer Research from the Ministry of Education, Science and Culture of Japan, and by a grant from the Naito Foundation.


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