Several nopaline degrading strains and one octopine degrading strain are shown to loose oncogenicity as well as the ability to utilize these guanidine compounds when they are cured of their TI plasmid. To investigate whether the specific genes involved in the utilization of one or the other compound are located on the plasmid, plasmid-transfer experiments have been performed. The plasmid from a nopaline degrading strain has been transferred to a naturally non oncogenic Agrobacterium namely A. radiobacter. Furthermore, the plasmid from an octopine degrading strain has been transferred to a plasmid-cured strain which originally had the capacity to utilize nopaline. Both kinds of experiments prove that the TI plasmid determines the strain specificity with regard to the utilization of either octopine or nopaline. They also demonstrate that the synthesis of either octopine or nopaline in crown gall cells is also determined by genes located on the TI plasmid harboured by the transforming A. tumefaciens strains.
In the course of our investigations on the PMR spectra of esters of pyrazoleacetic and pyrazolecarboxylic acids we became interested in the acidity of pyrazole acids. As far as we know ionisation constants are known of pyrazole-3(5)-carboxylic acid and of 3(5)-methylpyrazole-5(3)carboxylic acid only. Therefore, ionisation constants were determined for a few other pyrazolecarboxylic acids, pyrazole-1 -acetic acid and 3,5dimethvlpvrazole-1 -acetic acid (see Table).UV spectra of the last two acids and their ethyl esters were also determined (see experimental part). The absorption maxima of the pyrazole-1-acetic acids and their ethyl esters show similar changes going from neutral to aqueous acid solution as was found for alkylpyrazoles by Dal Monte et a1.3.From the ionisation constants of pyrazole-1-and 3,5-dimethylpyrazole-1acetic acids it follows that introduction of two methyl groups into the pyrazole nucleus results in a fairly large decrease in acidity. The pyrazolecarboxylic acids have the same acidity as the thiophene-and furan-carboxylic acids 4 . It appears that rather large difference in pK, value exists between 1,5-dimethylpyrazole-3-carboxylic acid and substituted-5-carboxylic acids, respectively (A pK, N 1). We hope to obtain more information concerning this difference in pK, values by investigating a number of other pyrazolecarboxylic and pyrazoleacetic acids.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.