Anderson A J, Dawes E A
Department of Applied Biology, University of Hull, United Kingdom.
Microbiol Rev. 1990 Dec;54(4):450-72. doi: 10.1128/mr.54.4.450-472.1990.
Polyhydroxyalkanoates (PHAs), of which polyhydroxybutyrate (PHB) is the most abundant, are bacterial carbon and energy reserve materials of widespread occurrence. They are composed of 3-hydroxyacid monomer units and exist as a small number of cytoplasmic granules per cell. The properties of the C4 homopolymer PHB as a biodegradable thermoplastic first attracted industrial attention more than 20 years ago. Copolymers of C4 (3-hydroxybutyrate [3HB]) and C5 (3-hydroxyvalerate [3HV]) monomer units have modified physical properties; e.g., the plastic is less brittle than PHB, whereas PHAs containing C8 to C12 monomers behave as elastomers. This family of materials is the centre of considerable commercial interest, and 3HB-co-3HV copolymers have been marketed by ICI plc as Biopol. The known polymers exist as 2(1) helices with the fiber repeat decreasing from 0.596 nm for PHB to about 0.45 nm for C8 to C10 polymers. Novel copolymers with a backbone of 3HB and 4HB have been obtained. The native granules contain noncrystalline polymer, and water may possibly act as a plasticizer. Although the biosynthesis and regulation of PHB are generally well understood, the corresponding information for the synthesis of long-side-chain PHAs from alkanes, alcohols, and organic acids is still incomplete. The precise mechanisms of action of the polymerizing and depolymerizing enzymes also remain to be established. The structural genes for the three key enzymes of PHB synthesis from acetyl coenzyme A in Alcaligenes eutrophus have been cloned, sequenced, and expressed in Escherichia coli. Polymer molecular weights appear to be species specific. The factors influencing the commercial choice of organism, substrate, and isolation process are discussed. The physiological functions of PHB as a reserve material and in symbiotic nitrogen fixation and its presence in bacterial plasma membranes and putative role in transformability and calcium signaling are also considered.
聚羟基脂肪酸酯（PHA）中，聚羟基丁酸酯（PHB）最为常见，是细菌广泛存在的碳和能量储备物质。它们由3-羟基酸单体单元组成，每个细胞中以少量细胞质颗粒的形式存在。20多年前，作为可生物降解热塑性塑料的C4均聚物PHB的特性首次引起了工业界的关注。C4（3-羟基丁酸[3HB]）和C5（3-羟基戊酸[3HV]）单体单元的共聚物具有改性的物理性能；例如，这种塑料比PHB脆性小，而含有C8至C12单体的PHA表现为弹性体。这类材料是相当大商业兴趣的核心，3HB- co - 3HV共聚物已由帝国化学工业公司（ICI plc）作为Biopol进行销售。已知的聚合物以2(1)螺旋形式存在，纤维重复距离从PHB的0.596 nm降至C8至C10聚合物的约0.45 nm。已经获得了具有3HB和4HB主链的新型共聚物。天然颗粒包含非晶态聚合物，水可能起到增塑剂的作用。虽然PHB的生物合成和调控一般已得到充分理解，但关于从烷烃、醇和有机酸合成长侧链PHA的相应信息仍然不完整。聚合酶和解聚酶的确切作用机制也有待确定。在真养产碱菌中，从乙酰辅酶A合成PHB的三种关键酶的结构基因已被克隆、测序并在大肠杆菌中表达。聚合物分子量似乎具有物种特异性。讨论了影响生物、底物和分离过程商业选择的因素。还考虑了PHB作为储备物质在共生固氮中的生理功能，以及它在细菌质膜中的存在及其在可转化性和钙信号传导中的假定作用。
