Does the newly discovered calpain 10 play a role in meat tenderization during post-mortem storage? Mohammad A. Ilian*, Alaa El-Din A. Bekhit, Roy Bickerstaffe Molecular Biotechnology Group, Animal and Food Sciences Division, PO Box 84, Lincoln University, Canterbury, New Zealand Received 19 December 2002; received in revised form 22 April 2003; accepted 22 April 2003 Abstract The objective was to study calpain 10 during meat tenderization. Western assays were developed and changes in calpain 10, tenderization level and desmin were determined in Longissimui (LTL) during post-mortem storage. A comparison between some characteristics of calpains 1, 2 and 10 indicated differences in the pI and sub-cellular distribution. Tenderness improved gradually during post-mortem storage and was accompanied by a decline in intact desmin level. Western analysis indicated that calpain 10 is present in sheep LTL probably as two proteins (MW 73.6 and 70.7 kDa). Post-mortem storage caused a decline in the level of the 73.6 and 70.7 kDa proteins in the sarcoplasmic fraction and a concomitant increase in these proteins in the myofibrillar fraction. Changes in the myofibrillar calpain 10 proteins were strongly correlated with the rate of tenderization. To conclude, calpain 10 proteins are present in sheep LTL and the sub-cellular distribution is dynamic during post-mortem storage. # 2003 Elsevier Ltd. All rights reserved. Keywords: Skeletal muscle; Tenderness; Desmin; Calpain 10 1. Introduction The variability in meat tenderness has been identified as a major consumer issue in New Zealand (Fraser, 1997) and this bears an economic penalty. From the meat industry’s point of view, tenderness is a function of production and processing. Solving this problem requires the determination of the critical points that regulate tenderness at the molecular level during pro- duction and processing of meat animals. The calpains (a family of intracellular Ca 2+ -dependent proteinases, EC 3.4.22.17, clan CA, family C02) are responsible for remodelling proteins that maintain the structure of ske- letal muscle (myofibrillar linkage proteins, MLP) such as titin, nebulin and desmin (Huff-Lonergan, Mitsuha- shi, Beekman, Parrish, Olson, & Robson, 1996; Pous- sard et al., 1996). It is the early post-mortem cleavage of these proteins that ultimately lead to the tenderization of meat (Taylor, Geesink, Thompson, Koohmaraie, & Goll, 1995). Calpains are classified on the basis of tissue distribu- tion into ubiquitous and tissue-specific. At the last count, the calpain proteolytic system in mammalian skeletal muscle is composed of eight ubiquitous (cal- pains 1, 2, 5, 7, 10, 12, 14 and 15) and one tissue-specific (calpain 3) isoenzymes. Calpains 5, 7, 10, 12, 14 and 15 were recently discovered (Dear & Boehm, 1999; Dear, Meier, Hunn, & Boehm, 2000; Franz, Vingron, Boehm, & Dear, 1999; Horikawa et al. 2000; Kamei, Webb, Young, & Campbell, 1998) but their biochemical role in skeletal muscle and meat tenderization is unknown. The function of the ubiquitous calpains 1 and 2 and the tis- sue-specific calpain 3 in meat tenderization has been the subject of many investigations (a comprehensive review was recently published by Hopkins & Thompson, 2002). A complete understanding of the mechanism of meat tenderization by the calpain proteolytic system requires the identification of the calpain isoenzymes catalyzing this process and their MLP substrates. Experimental evidence indicating a role for calpain 1 in post-mortem tenderization of meat is strong. Calpain 1 is terminally activated during post-mortem aging (Koohmaraie, 1992). The proteolysis of specific MLP by calpain 1 occurs at low pH and temperature and is similar to the 0309-1740/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0309-1740(03)00106-2 Meat Science 66 (2004) 317–327 www.elsevier.com/locate/meatsci * Corresponding author. Tel.: +64-3-3252-811x8137; fax: +64-3- 3253-851. E-mail address: alayanm@lincoln.ac.nz (M.A. Ilian).