Fig. 5. Effect of cysteine proteinase inhibitors E-64 and cystatin on the proteolytic activity of cathepsin L (left), as well as spicule extracts from S. domuncula (middle) and M. chuni (right). The activity of the samples was determined either directly (black columns), or following pretreatment with E-64 (dark grey columns) or cystatin (light grey columns). The proteolytic activity was measured with the synthetic substrate Z-Phe-Arg-AMC, and is given as nmol AMC released mg^–1 protein min^–1. Means (±s.d.) of five independent experiments are given.