Some aspects of riboflavin metabolism in the ruminant

Hart, Leigh I (1964) Some aspects of riboflavin metabolism in the ruminant. PhD thesis, University of Glasgow.

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1. The relationships between the xanthine oxidase activity, molybdenum content, and flavin-adenine dinucleotide (FAD) content of cow's milk, and between the xanthine oxidase activity and Molybdenum content of goat's milk, have been investigated. 2. A method for effecting quantitative release of the bound xanthine oxidase activity of cow's milk has been developed, and existing manometric and spectrophotometric methods for the determination of xanthine oxidase activity in milk have been modified and improved. With the aid of these improved methods it has been shown that, provided the diet of the cow is not supplemented with a soluble molybdate, a constant ratio of xanthine oxidase activity to molybdenum content is observed both in cow's milk and in purified xanthine oxidase isolated from cow's milk by the method of Gilbert & Bergel (1964). It follows from this observation that the inactive, molybdenum-containing "Xanthine oxidase" of Bray et al. (1961) must arise by inactivation of active xanthine oxidase during the isolation of this enzyme from cow's milk. It is shown that the estimated value of Bray et al. (1961) of 117 for the specific activity (activity/E1cm450) Or pure active bovine milk xanthine oxidase, is low. A nevi value of 150 is proposed for the specific activity of the pure enzyme. 3. The xanthine oxidase activity of goat's milk has been found to be very low compared with the activity of cow's milk. Molybdenum was found in all the samples of goat's milk that 'were examined, usually in concentrations slightly less than those found in normal cow's milk, but there was no correlation between the xanthine oxidase activities and molybdenum contents. in the goat's milks. 44 An inhibitor of bovine milk xanthine oxidase of unknown composition was found to be present in cow's milk. Neither the copper nor the orotic acid present in cow's milk were responsible for the inhibition. 5. The influence of dietary molybdenum intake on the xanthine oxidase activities of cow's and of goat's milks was investigated. It was found that with daily intakes of 5 mg. Mo/cow/day and 1.1 mg. Mo/goat/day, supplementary molybdenum (as sodium molybdate) was without effect on the xanthine oxidase activities of the milks of either cows or goats. 6. The manometric D-amino acid oxidase method for the determination of FAD has been modified and improved. It gave satisfactory results when applied to the determination of the FAD content of purified bovine milk xanthine ex1.46sa, but gave less satisfactory results when applied to the determination of the FAD content of cow's milk and of buttermilk. However, on the basis of the results obtained- by the use of this method, it is suggested that cow's milk contains an enzymically inactive ferroflavoprotein (the "xanthine oxidase" of Bray et al. 1961) which accompanies active xanthine oxidase throughout present procedures for the isolation of this enzyme from cow's milk. 7. In confirmation of earlier in the literature, a sample of purified bovine milk xanthine oxidase was found to possess some activity as coenzyme for the apo-protein of D-amino acid oxidase. The implications of this finding are discussed.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Animal sciences, Physiology
Date of Award: 1964
Depositing User: Enlighten Team
Unique ID: glathesis:1964-73230
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56

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