At least two transport systems serve for the entry of alanine, glycine, and serine into Escherichia coli. One of these systems serves mainly for glycine, D-alanine, and D-serine and to some extent for L-alanine, whereas the second serves for L-alanine and perhaps L-serine. These two transport systems have been characterized by kinetic studies and by inhibition analysis. Reciprocal plots for L-alanine entry are distinctly biphasic, giving rise to Km values of about 2 and 27 AM. The major route of glycine entry can be described by a single Km value of about 4 ,M. A higher Km value for glycine of around 70 to 100 uM shows that other routes of entry may serve at high concentrations of amino acid. The glycine, D-serine and D-alanine transport system is defective in a D-serine-resistant mutant, strain EM1302. The mutation, dagA, is recessive in dagA/dagA + merodiploids and is 7 to 12% linked by phage P1 transduction to the pyrB locus of E. coli. E. coli with the dagA mutation are unable to utilize D-alanine as a carbon source, providing an additional basis for selecting such mutants. The remaining L-alanine uptake in dagA mutants is subject to inhibition by L-serine, L-threonine, and L-leucine. It is also sensitive to osmotic shock treatment and repressed by growth of the cells on L-leucine. It appears from a comparison of the properties of the second L-alanine system with those of the leucine, isoleucine, and valine system (LIV system) that the LIV system also serves for the transport of L-alanine and L-threonine and perhaps L-serine. We previously reported that the amino acids alanine, serine, and glycine appeared to share a common transport system in Escherichia coli K-12 (17). An examination of the quantitative nature of the mutual inhibition among these amino acids in various strains of E. coli has revealed heterogeneity in the transport systems, particularly for the uptake of L-alanine (J. R.
The volatile plant sesquiterpenoids farnesene, nerolidol, and farnesol were tested to determine their effect on European corn borer,Ostrinia nubilalis, oviposition during the first six nights of the adult stage. Adult European corn borers were released into cages designed to encourage oviposition on eight glass plates randomly arranged on top of the cage: four coated with either 80µg/cm(2) farnesene, nerolidol, or farnesol, and four coated with the solvent methylene chloride. The setup was used as a binary choice test. Farnesene was preferred by females because they deposited significantly more egg masses on plates coated with the compound. Nerolidol had no effect. Farnesol, by contrast, deterred oviposition: the number of egg masses was significantly lower on plates covered with that compound. These data show that structural modification at a single terminal functional group in these compounds affects the ovipositional behavior of European corn borer females.
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