Lysosomal proteolysis in skeletal muscles of bulls

The relationship between lysosomal proteolytic enzyme activities involved in skeletal muscle proteolysis of the longissimus lumborum et thoracis muscle (MLLT) of bulls was described. Samples from the same region were obtained post mortem from 7 Piemontese (P) and 54 Black-and-White bulls (B-W) about 18 months old fed 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 proteinase inhibitor) acid (LIA) autolytic activities were measured in the presence of 1 mM Mg++. MLLT was also analysed for RNA, DNA and protein content. The data were processed by analysis of variance and differences between sires were tested by the contrast procedure of general linear model. In the examined muscle RNA decreased by 16% in B-W compared to P, CPS by about 14% and FCS by about 39%. DNA content was higher by 64.5% in B-W compared to P bulls (P ≤ 0.01). Some differences were found between P bulls and B-W groups of sires in the percentage of proteins (P ≤ 0.01), CatD and PSCatD (P ≤ 0.01), but the most pronounced differences were determined in PIA and LIA (P ≤ 0.01), and in the percentage of inhibition by pepstatin and leupeptin (P ≤ 0.01) in AAA. In the Black-and-White group of sires the percentage of protein and percentage of inhibition by pepstatin and leupeptin in AAA were lowered by about 10, 17 and 22%, but PSCatD, PIA and LIA were higher by about 23.7, 41 and 57.7%, respectively, compared to Piemontese bulls. The level of aspartic and thiol proteinases was lower in the muscles of B-W compared to Piemontese. The activity was much higher in B-W compared to P. These results indicate the faster turnover of proteins in the groups after Black-and-White sires and higher anabolic increase in degradation in Piemontese bulls.