Gel-filtration chromatography of the active fractions from the Mono-Q column marked by the horizontal bar in Fig. 1. Gel-filtration chromatography of the active fractions from the Mono-Q column marked by the horizontal bar in Fig. 1. Stiffening protein (H-tensilin) was eluted as the fourth small peak. The horizontal bar shows fractions with stiffening activity. Those with weak activity and with strong activity are indicated above the bar by `+' and `++', respectively. Masaki Tamori et al. J Exp Biol 2006;209:1594-1602 © The Company of Biologists Limited 2006