Metabolic characteristics of semitendinosus and gluteus medius muscles in bullfighting bulls at enzymatic level

Abstract

Muscle metabolic characteristics can be determined by the ratios between key enzymes of the main energy-supplying pathways. It was shown that enzyme groups of constant proportions exit and represent no variable units within the enzyme activity. This study was aimed at comparing the enzy- matic level of two bovine locomotor muscles. Biopsies were extracted from 24 male bullfighting bulls, aged between 4 and 5 years and belonging to four different Spanish farms. Four samples were taken from each animal: 2 from the semitendinosus muscle (ST) and 2 from the gluteus medius mus- cle (GM) at absolute depths of 30 and 50 mm. The activities of the enzymes CS (Krebs cycle oxida- tive potential), HAD (β-oxidation), HK (glucose phosphorylation), PHOS (glycogenolysis) and LDH (glycolytic capacity) were analysed. The following enzyme ratios were considered: PHOS/LDH; HK/CS; HAD/CS; LDH/CS and PHOS/HK. Some metabolic characteristics between both muscles and depths were found. No significant differences were detected in the HK/CS ratio in the ST and in the GM, whereas the LDH/CS ratio was higher in the ST at 30 mm and in the GM at 50 mm. No dif- ferences were detected between both depths in the GM muscle, for the HK/CS ratio and LDH/CS ratio. In contrast, in the ST muscle, the LDH/CS and HK/CS ratios were statistically higher at 30 than at 50 mm depth. The most evident differences were observed when the four farms were compared. This study showed that the main metabolic differences between the bovine ST and GM muscles were the relationships between the capacities to use extracellular energy sources, to oxidise Acetyl CoA in the Krebs cycle and to reduce pyruvate to lactate.