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Pantothenate kinase catalyzes the rate-controlling step in coenzyme A (CoA) biosynthesis and is regulated by feedback inhibition by CoA. Pantothenate kinase was purified to homogeneity from Escherichia coli and was shown to exist as a homodimer. Kinetic analysis indicated the presence of two ATP binding sites that exhibited positive cooperativity with a Hill coefficient of 1.46. Site-directed mutagenesis of lysine 101 to methionine (K101M) resulted in the inactivation of the enzyme, although dimer formation was not altered. The K101M mutant was unable to bind either adenosine 5'-O-(3-thiotriphosphate) or CoA, supporting the conclusion from kinetic analysis that both the substrate and inhibitor bind to the same site on the enzyme. CoA binding was not cooperative. Coexpression of the K101M mutant gene on a high copy number plasmid in the presence of a chromosomal copy of the wild-type gene resulted in the production of heterodimers between active and inactive subunits. Kinetic analysis of the chimeric heterodimers showed the absence of cooperative ATP interactions and indicated a sequential kinetic mechanism for pantothenate kinase with ATP binding first and pantothenate second. Thus, pantothenate kinase regulation involves the competitive binding of CoA to the ATP site, which blocks ATP binding at one site and prevents positive cooperative ATP binding to the second site on the dimer.

Pantothenate kinase catalyzes the rate-controlling step in coenzyme A (CoA) biosynthesis. The structural gene (coaA) located at 90 min of the Escherichia coli chromosome was cloned and sequenced. The coaA gene was transcribed in the opposite direction to the flanking genes birA and thrU and produced a single 1.1-kb transcript. Translation of the coaA gene produced two protein products (36.4 and 35.4 kDa) that differed by eight amino acids at the amino terminus. The poor homology of the coaA promoter region to consensus E. coli promoter sequences and the low frequency of optimal codon usage (0.565) were consistent with the low abundance of pantothenate kinase. Strains containing multiple copies of the coaA gene possessed 76-fold-higher specific activity of pantothenate kinase; however, there was only a 2.7-fold increase in the steady-state level of CoA. These data corroborate the conclusion that regulation of pantothenate kinase activity by feedback inhibition is the critical factor controlling the intracellular CoA concentration.

This study evaluated the efficacy of gamma irradiation to inactivate food‐borne pathogens on pistachios (Pistacia vera L.). Pistachios inoculated with Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes were subjected to gamma irradiation in the range of 0, 0·5, 1, 3 and 5 kGy, and colour change was evaluated after treatment and during storage at room temperature. Pathogen populations decreased with increasing treatment doses. A gamma irradiation dose of 5 kGy decreased the three pathogens on pistachios to under the detection limit (1·0 log CFU per g) without effecting colour change. During storage following treatment, pathogens were reduced due to the postirradiation effect. D‐values of pathogens on pistachios showed that L. monocytogenes was more resistant to gamma irradiation than was E. coli O157:H7 or S. Typhimurium. During gamma irradiation treatment, L, a and b values of pistachios did not significantly change but these values changed during storage. These results show that gamma irradiation has potential as a nonthermal process for inactivating food‐borne pathogens in pistachios without inducing colour changes. Significance and Impact of the Study: Generally, nuts have lower water activity which precludes the growth of food‐borne pathogens. But, food‐borne outbreaks due to pathogen‐contaminated nuts have been reported in the last few decades. Pistachios are one of the most popular nuts and have many health beneficial effects. However, many pasteurization interventions have been used to reduce pathogens on pistachios, but most of them are not effective. This study confirms the effectiveness of gamma irradiation on pasteurization of pistachios. This may be helpful in nut processing industries to ensure the microbial safety of nuts. Significance and Impact of the Study: Generally, nuts have lower water activity which precludes the growth of food‐borne pathogens. But, food‐borne outbreaks due to pathogen‐contaminated nuts have been reported in the last few decades. Pistachios are one of the most popular nuts and have many health beneficial effects. However, many pasteurization interventions have been used to reduce pathogens on pistachios, but most of them are not effective. This study confirms the effectiveness of gamma irradiation on pasteurization of pistachios. This may be helpful in nut processing industries to ensure the microbial safety of nuts. [ABSTRACT FROM AUTHOR]

Aims This study evaluated the combined effects of ozone and heat treatment to inactivate Escherichia coli O157:H7 and Salmonella Typhimurium in three types of apple juice of different soluble solids content. Methods and Results Three types of apple juice (18, 36, 72 °Brix) inoculated with pathogens were subjected to ozone (3·0 l min−1 flow rate and 2·0-3·0 g m−3 concentration) and heat treatment (25, 45, 50 and 55°C) simultaneously for 20, 40 and 60 s. Initial populations of pathogens in inoculated apple juice were approximately 105-106 CFU ml−1. Heat treatment alone (25, 45, 50 and 55°C) for 1 min reduced populations of E. coli O157:H7 by 0 to 4·75 log CFU ml−1 in three types of apple juice. The combination of ozone and heat treatment for 1 min at 25 and 45°C reduced E. coli O157:H7 by 0·93-3·87 log CFU ml−1 and below the detection limit (>1 log CFU ml−1) at 50 and 55°C. A similar tendency was observed for S. Typhimurium. In several instances, results showed a synergistic effect of ozone and heat treatment. Colour values were not changed during ozone and heat treatment. Conclusion These results show that the combination of ozone and heat treatment can be used as a potential inactivation intervention for E. coli O157:H7 and S. Typhimurium in apple juice. Significance and Impact of the Study The combination of ozone treatment and mild heat can be used as an alternative intervention for pasteurization of varying soluble solids content apple juice in food industries. [ABSTRACT FROM AUTHOR]