Schwägele F, Buesa P L, Honikel K O
Institut für Chemie und Physik, Bundesanstalt für Fleischforschung, E.-C.-Baumann-Strasse 20, D-95326 Kulmbach, Germany.
Meat Sci. 1996 Sep;44(1-2):41-53. doi: 10.1016/s0309-1740(96)00045-9.
In order to investigate the cell biological causes for the fast breakdown of glycogen which is observed during the development of the PSE (pale, soft, exudative) syndrome in muscles of stress-susceptible pigs, muscle glycogen phosphorylase (GP) as a key enzyme in two isoforms, a and b, of the energy turnover was isolated from M. longissimus dorsi of normal and PSE-prone pigs of the German Landrace. GP b as well as GP a from normal and PSE-muscles exist in a dimeric form with a molecular weight of 97 000 D per subunit. The tendency for tetramerization of GP b increases in the presence of ATP, whereas the enzyme activity is simultaneously inhibited. The catalytic activities of GP a and GP b from both groups of animals show an optimum at pH 7.0. GP b can be activated to GP a by phosphorylation with the result of a 25% higher optimum specific activity in the case of normal and PSE-muscles. In interaction with glycogen and glucose-1-phosphate GP b follows the characteristics of a Michaelis-Menten kinetic, whereas the binding of AMP and phosphate proves to be allosteric. In comparison of the structural and kinetic characteristics of GP from normal as well as PSE-muscles no significant differences could be determined, indicating that GP does not belong to those factors which are triggering an accelerated energy turnover of ATP in muscles of stress-susceptible pigs.
为了探究应激敏感型猪肌肉中出现PSE（苍白、柔软、渗出）综合征时糖原快速分解的细胞生物学原因，从德国长白猪正常和易患PSE的猪的背最长肌中分离出肌肉糖原磷酸化酶（GP），它是能量代谢两种同工型a和b中的关键酶。正常肌肉和PSE肌肉中的GP b以及GP a均以二聚体形式存在，每个亚基的分子量为97 000 D。在ATP存在的情况下，GP b的四聚化趋势增加，而酶活性同时受到抑制。两组动物的GP a和GP b的催化活性在pH 7.0时表现出最佳值。GP b可通过磷酸化激活为GP a，正常肌肉和PSE肌肉的最佳比活性提高25%。在与糖原和葡萄糖-1-磷酸相互作用时，GP b遵循米氏动力学特征，而AMP和磷酸盐的结合被证明是变构的。比较正常肌肉和PSE肌肉中GP的结构和动力学特征，未发现显著差异，这表明GP不属于引发应激敏感型猪肌肉中ATP加速能量代谢的因素。
