TUMORAL MYOSINS OF NI3S2-INDUCED RHABDOMYOSARCOMAS IN RAT AND RABBIT - COMPARATIVE STUDIES WITH ADULT AND FETAL MYOSINS OF SKELETAL-MUSCLE

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  • 1 January 1980
    • journal article
    • research article
    • Vol. 20  (3) , 240-248
Abstract
Tumoral myosins were isolated from rat and rabbit rhabdomyosarcomas and compared with normal adult and fetal skeletal myosins. The synthetic filaments, the L-chain composition and the Ca2+-ATPase activity were studied. In the presence of Mg2+, normal myosins precipitated as bipolar filaments (0.5 .mu.m), fetal and tumoral myosins, however, precipitated as long fusiform filaments (1-10 .mu.m). SDS-PAGE [sodium dodecyl sulfate-polyacrylamide gel electrophoresis] revealed that tumor myosins contain the same L-chains as fetal myosin (25,000 and 18,000 daltons, L25-L18). The 3rd L-chain of the normal muscle myosin (16,000 daltons, L16) was absent. In addition, Urea-PAGE revealed the absence of the phosphorylated form of the L18 in fetal and tumor myosins. Ca2+ ATPase activity measurements performed in function of the Ca2+ concentration showed similarities between fetal and adult muscle myosins. The Ca2+-ATPase activity of tumor myosins, however, was very low and slightly activated by increasing the Ca2+ concentration (0.01-10 mM). Fetal and tumor myosins are identical as to the ultrastructure of their synthetic filaments and their L-chain composition. This was not so in regard to the Ca2+-ATPase activity. This is probably the result of the expression of a new myosin or of 1 of its polypeptides, which has a different Ca2+-ATPase activity.

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