The pta gene encoding phosphotransacetylase was cloned on a high copy plasmid with or without the ackA gene encoding acetate kinase in Escherichia coli. The acetate kinase and phosphotransacetylase were overproduced in cells harboring the plasmid possessing both genes. Nucleotide sequencing of the pta gene revealed that it is able to produce a polypeptide comprising 714 amino acid residues, which starts at 70 base pairs downstream from the stop codon of the ackA gene. The 77-kDa protein band of overproduced phosphotransacetylase was observed on SDS-polyacrylamide gel electrophoresis, of which the amino terminal sequence corresponds to that of the deduced polypeptide without the amino terminal methionine. Two transcripts of pta of different sizes were found in the cells. A 3,700 nucleotide transcript, which covers the ackA and pta genes, seemed to be produced by the first promoter in the operon and a 2,300 nucleotide transcript, which covers just pta, seemed to be produced by the second promoter. In a synthetic medium containing acetate as the sole carbon source, the growth of an ackA-pta double mutant was greatly impaired. Complementation analyses revealed that both the acetate kinase and phosphotransacetylase were required for the rapid growth in the acetate medium.

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Escherichia coli grown in a rich medium excreted acetate and reused the acetate. Using cloned genes and a plasmid with a temperature-sensitive replication origin, three kinds of Pta-Ack pathway deletion mutants were constructed. Acetate production and reuse by wild-type cells grown in the rich medium was confirmed to largely occur through the Pta-Ack pathway. The deletion mutants of the gene encoding phosphotransacetylase secreted pyruvate before the secretion of acetate into the medium. A deletion mutant of the gene encoding acetate kinase grew at a slow rate, but its secretion and use of acetate were rapid. These results indicated that a pathway(s), other than the Pta-Ack pathway, functions in the control of excess carbon flow in the mutants.

To study the effectiveness of photosensitizers to accelerate the degradation of cellulose acetate (CA) under ambient environment, CA (degree of substitution ¼ 2.45) films containing benzophenone, which is one of the typical photosensitizers, were prepared and their degradative behavior by photoirradiation was examined. Decrease in molecular weight of CA and generation of carbon dioxide, carbon monoxide, and acetic acid from the CA films were observed by the irradiation of xenon arc lamp light, which was passed through a filter for cutting off the wavelength shorter than 275 nm. With increasing the concentration of benzophenone, the molecular weight of CA decreased and the generation of the degradation products from the CA films increased. These results may suggest that radical reactions of CA films proceed by photoirradiation and lead to oxidation and random cleavage of CA, and that benzophenone is an effective additive to accelerate the degradation of CA under ambient environment.