抄録
Our AFM studies revealed that the transverse stiffness and its distribution are different for cardiac and skeletal myofibrils and it was differently affected by proteolytic treatments for the two myofibrils. To give a molecular basis for these findings, in the present study, we investigated how differently molecular components of cardiac and skeletal myofibrils were digested by proteolytic treatments.
Single myofibrils were prepared by homogenizing glycerinated muscle fibers of the left ventricle of rat heart and the rabbit psoas muscle. Proteolytic digestions of myofibrils were made by calpain and trypsin. SDS-PAGE was performed on 2.5%~12% gradient gels.
By the calpain treatment, α-actinin in cardiac and skeletal myofibrils was degraded although its rate was slow for cardiac myofibrils and very fast for skeletal myofibrils. Connectins in both myofibrils and nebulin in skeletal myofibrils were also degraded while other muscle proteins were almost not degraded. By the trypsin treatment, connectin in both myofibrils and nebulin in skeletal myofibrils were degraded although their degradation products were different for cardiac and skeletal myofibrils. And α-actinin and other muscle proteins were almost not degraded. These results suggested that the difference in the mechanical characteristics between cardiac and skeletal myofibrils is based on the difference in the molecular structures of the two myofibrils. [Jpn J Physiol 54 Suppl:S120 (2004)]
