A kinetic study of glycogen phosphorylase b from the mantle tissue of Mytilus galloprovincialis,Lmk |
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| Affiliation: | 1. Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, China;2. Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi 214122, China;3. Shenzhen Key Laboratory of Steroid Drug Discovery and Development, Warshel Institute for Computational Biology, School of Life and Health Sciences, The Chinese University of Hong Kong (Shenzhen), Shenzhen 518172, China |
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| Abstract: | - 1.1. In order to assign a meaningful role to the phosphorolytic pathway in Mytilus glycogen metabolism the kinetic mechanism of phosphorylase b, and its allosteric control, were studied.
- 2.2. The kinetic parameters of phosphorylase b from the mussel Mytilus galloprovincialis were determined. Michaelis constants (Km or S0.5) were in the range of 0.32–2.49 mg/ml for glycogen, 7–16 mM for Pi and 114–423 μM for AMP. In the direction of glycogen synthesis, the Km value for glucose-1-P was approximately 180 mM.
- 3.3. The enzyme displayed homotropic co-operativity towards the binding of co-substrate and AMP (Hill coefficients of 2 and 1.4, respectively) and heterotropic co-operativity between substrates and AMP.
- 4.4. The concentration of glycogen in the Mytilus mantle is between 38- and 125-fold higher than the apparent Km of phosphorylase b; the concentration of AMP varies throughout the year from 10 to 175 μM, up to a value close to the apparent Km for the effector.
- 5.5. The apparent Km for Pi is close to the concentration found in the mantle. This ligand showed more important regulatory effects than the effector AMP.
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