Includes bibliographical references (p. 77-86).

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

No description available.

A graphical method, based on a set of acid-base titrations, is presented for the determination of the carbon dioxide speciation in natural solutions. The application of this method, in conjunction with measurements of the partial pressure of carbon dioxide with which our solutions were in equilibrium permitted the calculation of the solubility of carbon dioxide. The results of these calculations in dilute solutions of 1.00 meq/l alkalinity gave a value of 0.070 for the solubility at 25° C. This value is considerably higher than that obtained by Harned and Davis (1943), 0.0345, for solutions of zero alkalinity. Our experimental method, with the conditions used by Harned and Davis, yielded a result which agreed well with theirs. It is concluded that the solubility of carbon dioxide within the alkalinity range found in many fresh waters, is greater than was previously believed. The reason for this higher solubility is not known. It is shown that it cannot be ascribed to a specific cation effect. / Graduation date: 1969

No description available.

No description available.

No description available.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2001. / Härtill 4 uppsatser.

Proefschrift-Technische Hoogeschool, Delft. / "Summary": p. [140]-141. "Stellingen": [2] p. inserted. "Literatuuroverzicht": p. [142]-144.

Proefschrift-Technische Hoogeschool, Delft. / "Summary": p. [140]-141. "Stellingen": [2] p. inserted. "Literatuuroverzicht": p. [142]-144.