Uchino Keiichi, Saito Terumi
Laboratory of Molecular Microbiology, Department of Biological Sciences, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293.
J Biochem. 2006 Mar;139(3):615-21. doi: 10.1093/jb/mvj069.
Poly(3-hydroxybutyrate) (PHB) is synthesized from 3-hydroxybutyryl-CoA by polyhydroxyalkanoate synthase and hydrolyzed by PHB depolymerase. In this study, we focused on the reverse reaction of polyhydroxyalkanoate synthase, and propose the possibility that PHB can be degraded through a novel process, that is thiolysis of PHB with CoASH. Polyhydroxyalkanoate synthase of Ralstonia eutropha was incubated with 14C-labeled PHB and CoASH. The reaction mixture was fractionated by HPLC and then analyzed with a scintillation counter. The analysis revealed 3-hydroxybutyryl-CoA to be a product of the reaction. When NADP+ and acetoacetyl-CoA reductase were added to the reaction mixture, an increase in absorbance at 340 nm was observed. Native PHB inclusion bodies from R. eutropha also showed thiolytic activity. This is the first indication that polyhydroxyalkanoate synthase catalyzes both the synthesis and degradation of PHB, and that native PHB inclusion bodies has thiolytic activity.
聚（3-羟基丁酸酯）（PHB）由聚羟基脂肪酸酯合酶从3-羟基丁酰辅酶A合成，并由PHB解聚酶水解。在本研究中，我们关注聚羟基脂肪酸酯合酶的逆反应，并提出PHB可通过一种新过程降解的可能性，即PHB与辅酶A进行硫解反应。将真养产碱菌的聚羟基脂肪酸酯合酶与14C标记的PHB和辅酶A一起孵育。反应混合物通过高效液相色谱法进行分离，然后用闪烁计数器进行分析。分析表明3-羟基丁酰辅酶A是该反应的产物。当向反应混合物中加入NADP +和乙酰乙酰辅酶A还原酶时，在340nm处观察到吸光度增加。来自真养产碱菌的天然PHB包涵体也表现出硫解活性。这首次表明聚羟基脂肪酸酯合酶催化PHB的合成与降解，并且天然PHB包涵体具有硫解活性。
