The discovery of troponin by Professor Setsuro Ebashi opened a new era for research
into the regulation of striated muscle contraction. This volume is the proceedings of the symposium
held at Okazaki, Japan, in 2005 celebrating the 40th anniversary of that discovery.
Professor Ebashi started his work on muscle contraction when he was a young
researcher, immediately after World War II, having been inspired by the book Chemistry
of Muscular Contraction by Albert Szent-Györgyi. He was fascinated by the dynamic
features of the contractile processes performed by the two contractile proteins, myosin
and actin, in the presence of ATP. However, he wondered about the mechanism by which
muscle relaxes after contraction. He proceeded with biochemical studies of muscle relaxation
and found in 1952 that a factor present in the supernatant of the suspension of
minced frog skeletal muscle caused relaxation of glycerinated muscle fibers. Based on
this finding and succeeding work, he came to the conclusion that the relaxation of contracted
muscle was caused by the uptake of calcium ions from the cytosol into the relaxing
factor (sarcoplasmic reticulum). His work greatly contributed to elucidating the entire
processes of excitation–contraction coupling, particularly the role of calcium ions in triggering
the contractile response of myofibrils.
Then he found that superprecipitation of actomyosin, i.e., an in vitro contraction
model, became sensitive to calcium ion concentration in the presence of a protein factor
other than myosin and actin. This factor showed some similarity to tropomyosin, which
had been reported by Bailey, and thus was called native tropomyosin.
When I started working in Professor Ebashi’s laboratory in 1963 as a graduate
student, he was working very hard with his wife to characterize the biochemical properties
of native tropomyosin. Tropomyosin, reported by Bailey, was actually isolated by
isoelectric precipitation from native tropomyosin, but it did not confer any calcium sensitivity
to actomyosin. In 1965, Professor Ebashi succeeded in isolating a new protein
named “troponin” from native tropomyosin, which, in association with tropomyosin,
made actomyosin sensitive to calcium ions. With a series of studies in the 1960s, the
molecular basis for the regulation of muscle contraction was established. Since that time,
troponin has been the central object in research on the regulation of striated muscle contraction.
Properties of troponin, which consists of three different components, have been
extensively investigated as revealing insights into a representative calcium-receptive and
Professor Ebashi and I sincerely hoped that this volume would become a milestone
for future developments in the study of the regulation of muscle contraction and related
biomedical sciences. I would like to express my profound gratitude to all contributors for
their heartfelt cooperation.