Electron microscopic filament lengths of connection and its fragments.

Connectin (titin) is an extraordinarily long filamentous protein of striated muscle. The particle lengths of alpha-connectin (titin 1) and its proteolytic products, beta-connectin (titin 2) and 1,200 kDa fragment, were measured with rotary-shadowed images of the filaments after orientation by centrifugation. It was observed that the 1,200 kDa fragment was frequently folded into a double strand, beta-connectin was partly folded, and alpha-connectin was easily split into beta-connectin and 1,200 kDa fragment. Taking these features into consideration, the average lengths of alpha- and beta-connectin and 1,200 kDa fragment were estimated to be approximately 1,250, 920, and 360 nm, respectively.