Cathepsin involvement in muscle proteolysis in meat-type bulls

Abstract

Measurements were done of some lysosomal proteolytic enzyme activities involved in skeletal muscle proteolysis of the masculus longissimus lumborum et thoracis muscle (MLLT) of bulls. Samples from the same region between the 11th and 13th vertebra were taken after slaughter from Limousin (n = 10), Hereford (n = 10), Charolais (n = 10), Angus (n = 11) and Simmental (n = 11) bulls about 15 months old fed complete diet ad libitum. The activity of cathepsin D was determined as pepstatin (cathepsin D inhibitor) sensitive activity (PSCatD) towards 1% haemoglobin. Pepstatin-insensitive acid (PIA) and leupeptin-insensitive (thiol proteinases inhibitor) acid (LIA) autolytic activities were measured in the presence of 1mM Mg<sup>++</sup>. MLLT was also analysed for RNA, DNA and protein variables. The data were processed by analysis of variance. The highest activities in PSCatD (P ≤ 0.05), AAA (P ≤ 0.01) and LIA (P ≤ 0.05) as well as percentage of inhibition by pepstatin in cathepsin D (P ≤ 0.01) were estimated in Angus bulls, and the lowest in Limousin ones. These breeds differed in the above-mentioned activities by 20.3, 21.1, 31.1 and 13.1%, respectively. RNA/g of tissue was highest in Hereford and lowest in Limousin bulls (by about 15.3%, P ≤ 0.01). Similar differences (14.3%) were between Charolais and Limousin (P ≤ 0.01). CPS (10<sup>3 </sup>RNA/protein) was higher by 18.3% (P ≤ 0.01) in Charolais compared to the value in Simmental bulls; similar differences were between Hereford and Simmental (16.4%, P ≤ 0.01). The DNA concentration was highest in Hereford (by about 30%) compared to Charolais bulls. Protein/10<sup>3</sup>DNA ratio (mg/mg) – FCS – was higher by 33.4% in Charolais compared toHereford; RNA/DNA ratio was higher by 40.2% in Charolais compared toLimousin bulls. These results indicate the fast turnover of proteins in the groups of examined bulls and it can be concluded that in hypertrophic MLLT of bulls an anabolic decrease in degradation occurred.