Rhie H G, Dennis D
Department of Biology, Kyung Hee University, Seoul, Korea.
Can J Microbiol. 1995;41 Suppl 1:200-6. doi: 10.1139/m95-188.
In Escherichia coli carrying the poly(3-hydroxyalkanoate) (PHA) biosynthesis pathway on a plasmid (pha+), the function of the ackA (acetate kinase) and pta (phosphotransacetylase) genes is necessary for efficient incorporation of 3-hydroxyvalerate (3-HV) into the copolymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)). Recombinant pha+ E. coli fadR atoC(Con) strains possessing mutations in ackA, pta, or both ackA and pta exhibited substantially reduced levels of 3-HV formation. Conversely, the same strains carrying the ackA gene on a multicopy plasmid exhibited an increase in 3-HV formation concomitant with a large increase in acetate kinase activity. However, if the strain possessing the multicopy ackA+ plasmid was mutant at the pta locus, it lost the ability to incorporate significant amounts of 3-HV into P(3HB-co-3HV). In addition to the ackA pta pathway, there is an inducible activity that can also mediate the incorporation of 3-HV into P(3HB-co-3HV). This pathway is repressed by glucose and is not normally operative in P(3HB-co-3HV) production in recombinant pha+ E. coli strains that are grown using glucose as the major carbon source. It appears likely that this activity is due to an inducible acetyl-CoA synthetase that converts propionate to propionyl-CoA.
在携带质粒上聚（3-羟基链烷酸酯）（PHA）生物合成途径（pha+）的大肠杆菌中，ackA（乙酸激酶）和pta（磷酸转乙酰酶）基因的功能对于将3-羟基戊酸（3-HV）有效掺入共聚物聚（3-羟基丁酸酯-co-3-羟基戊酸酯）（P（3HB-co-3HV））中是必需的。在ackA、pta或ackA和pta两者中具有突变的重组pha+大肠杆菌fadR atoC(Con)菌株表现出3-HV形成水平大幅降低。相反，在多拷贝质粒上携带ackA基因的相同菌株表现出3-HV形成增加，同时乙酸激酶活性大幅增加。然而，如果具有多拷贝ackA+质粒的菌株在pta位点发生突变，它就失去了将大量3-HV掺入P（3HB-co-3HV）的能力。除了ackA pta途径外，还有一种可诱导活性也能介导3-HV掺入P（3HB-co-3HV）。该途径受葡萄糖抑制，在以葡萄糖作为主要碳源生长的重组pha+大肠杆菌菌株的P（3HB-co-3HV）生产中通常不起作用。这种活性似乎是由于一种可诱导的乙酰辅酶A合成酶将丙酸转化为丙酰辅酶A所致。
