Post-mortem activity of the glycogen debranching enzyme and change in the glycogen pools in porcine M. longissimus dorsi from carriers and non-carriers of the RN(-) gene.

Glycogen debranching enzyme (GDE) is together with glycogen phosphorylase responsible for the degradation of glycogen. The present study compares the post-mortem activity of GDE and breakdown of the glycogen pools in M. longissimus dorsi of RN(-) carrier pigs and in wild type animals. The activity of GDE (n=14) and pH (n=20) was measured 0.5, 3, 5, 24 and 48h post-mortem. The change in pro-glycogen and in macro-glycogen content (n=20) was followed until 216h post-mortem and the transcription level of GDE, glycogenin and glycogen synthase m-RNA (n=19) were measured 0.5h post-mortem. Both the activity of GDE and the transcription level of GDE were found to be similar in RN(-) carriers and wild type animals shortly after slaughter. However, the activity declined faster in wild type animals compared with RN(-) carriers with increasing time post-mortem. The contents of both pro-glycogen and macro-glycogen were higher in RN(-) carriers compared with wild type animals, and further, the proportion of macro-glycogen was higher in RN(-) carriers compared with wild type animals. During the post-mortem period, only degradation of pro-glycogen was observed in both genotypes. The decrease in pH was faster and the ultimate pH lower in RN(-) carriers than in wild type animals. It was suggested that the higher GDE activity in the late phase of the post-mortem period in muscles from RN(-) carriers renders the extended pH decrease in these muscles.