Fig. 6. Identification of the 27 kDa protein species in the total extract obtained from M. chuni giant basal spicules. (A) An extract from lamellae (la) of giant basal spicule was obtained and subjected to 10% SDS-PAGE. The 27 kDa protein is stained with Coomassie Brilliant Blue (lane a). M, size markers. (B) For the reaction with the labelled inhibitor (biotinylated E-64) the Monorhaphis spicule proteins were blot transferred and reacted with biotinylated E-64 as described under Materials and methods. The binding reaction with this reagent was performed either by direct addition of biotinylated E-64 to the blot (lane a, –; the 27 kDa protein is labelled) or after a pretreatment of the blot with a surplus of unlabelled E-64 (lane b, +).