Inhibition of polyphenol oxidase (PPO) by sulfur dioxide (SO₂) was studied using three different sources of PPO (banana, mushroom, and pear). Several methods to detect PPO activity were tested due to SO₂, interference in some of the assays. The method using 2-nitro-5-thiobenzoic acid (TNB) to react with the quinones was found to be the most reliable for assaying PPO activity in the presence of SO₂ whereas, the oxygen electrode and spectrophotometric methods were not suitable. When PPO was exposed to SO₂ prior to the substrate addition, it was inhibited irreversibly. Trials to regenerate the PPO activity using extensive dialysis, column chromatography, and addition of copper salts were not successful. Experiments using Cu(II) and the TNB method to regenerate the activity of the pear PPO apoenzyme that was not exposed to SO₂, also showed the turnover between Cu(I) and Cu(II) during the enzyme oxidation of o -phenols. Increased concentrations of SO₂ and pH less than 5 enhanced the inhibition of PPO by SO₂. At pH 4 concentrations greater than 20 ppm completely inhibited 1,000 units of PPO activity almost instantaneously. This suggests SO₂ as such as the main form inhibiting PPO. Kinetic studies confirmed the irreversibility of the inhibition. Purified pear PPO was used to determine binding of ³⁵SO₂ to the enzyme. Column chromatography, extensive dialysis and gel electrophoresis did not show SO₂ bound to PPO protein. Formation of extra bands on gel electrophoresis in the SO₂ inhibited pear PPO fractions was demonstrated. This and other evidence suggests that there was a modification of the protein structure of PPO, with retention of protein integrity. Also it is suggested that this was the main mode of direct irreversible inhibition of PPO by SO₂. / Graduation date: 1984

xx, 108 leaves : tables, graphs ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Agricultural Biochemistry, 1977

Thesis (M.Ag.Sc. 1971) from the Dept. of Agricultural Biochemistry, University of Adelaide.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Agricultural Biochemistry, 1977.

This thesis is divided into three chapters. The first chapter is a review of the literature methods utilised to date in the synthesis of non-racemic chiral sulfoxides, including resolution, stereospecific nucleophilic substitution at sulfur, asymmetric oxidation and enzymatic methods Also, this first chapter introduces briefly the palladium-catalysed allylic nucleophilic substitution reaction. It covers the nature of different factors which can influence on the enantiomeric excess. The second section deals with our approaches to the synthesis of potentially chelating sulfoxides of high enantiomeric purity and their subsequent application, mainly in the process of palladium-catalysed allylic nucleophilic substitution reactions as chiral ligands, but also their application as chiral auxiliaries in the synthesis of chiral α-hydroxy or α-amino ketones. This second chapter also deals with the design of a new class of chiral ammo-sulfides as ligand in the palladium-catalysed allylic nucleophilic substitution reaction. The most successful ligand synthesised enantiomerically pure N-(1,1-dimethylethyl)-N-(1S,2S)-2-[(1,1-dimethylethyl)thio]-1-methyl-2-phenylethyl-N-methylamine was applied successfully to the palladium-catalysed allylic nucleophilic substitution reaction, furnishing the product in up to 89% ee. The third part of this thesis deals with the experimental procedures undertaken in this work.

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Among the insecticides, lime- sulphur is one of growing importance. Already it has found extensive use as a spray on all kinds of fruit trees, shrubs and vines and is also largely employed as an animal dip for scab diseases, and for the extermination of lice in hen houses. It is especially adapted for the destruction of soft-bodied scale insects on fruit trees, such as the San Jose Scale.

[Truncated abstract] The ‘elemental sulphur’ deposition problem is a fairly recent phenomenon for gas transmission pipelines. Although known for a number of decades to cause plugging in reservoir wellhead facilities, it is since about 1990 that ‘elemental sulphur’ deposition has openly been acknowledged as a problem in natural gas pipelines and other facilities downstream of gas processing plants. Within the past ten years this formation / deposition process has progressively been more widely observed. The increasing trend to have transmission pipeline systems operating at higher pressures is a significant contributing factor in the formation of “elemental sulphur”. This research project has been able to identify the principles and mechanisms associated with the formation and deposition ‘sulphur vapour map’ concept, that only sub ppm levels of sulphur vapour within the gas stream is required to initiate the “elemental sulphur” formation / deposition process. The ‘sulphur vapour map’ can be used in predicting the degree of sulphur vapour desublimation that will occur for given pipeline operating conditions of pressure, temperature and gas composition. This, in turn, will assist in the minimization of the deposition process through the ability to make simple, yet appropriate, modifications to the design of the required pipeline pressure regulation stage. A significant number of other potential contributing factors to this pipeline particle formation and deposition process have also been identified through this research work. From these findings a number of additional recommendations have been made that will assist pipeline operators in minimizing the impact of this deposition problem. These recommendations are based on the operation of the pipeline, and particularly the control of the entry of liquids and other contaminants into the pipeline system. Recommendations for further research into this complex problem are also made.

Thesis (M.S.)--Oregon State University, 2005. / Printout. Includes bibliographical references. Also available on the World Wide Web.

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