Purification and partial characterization of ostrich skeletal muscle cathepsin D and its activity during meat maturation

Cathepsin D was purified from ostrich (Struthio camelus) skeletal muscle using pepstatin-A chromatography. The enzyme was comprised of two subunits (29.1 and 14 kDa). The N-terminal amino acid sequence of both subunits were determined and showed high amino acid sequence identity to other cathepsin D homologs. Ostrich cathepsin D was optimally active at pH 4 and at a temperature of 45 °C, and was strongly inhibited by pepstatin-A (Ki = 3.07 × 10− 9 M) and dithiothreitol. Cathepsin D activities from five ostriches were monitored over a 30-day period. Cathepsin D remained substantially active throughout the 30-day storage period with an average remaining activity of 112 ± 8.57% at day 30 (mean value from 5 ostriches).