Graduate Thesis Or Dissertation
 

Biological oxidation of sorbitol

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  • The oxidation of sorbitol by soluble extracts of A. suboxydans proceeds by two pathways depending upon which pyridine nucleotide is present. In the presence of TPN, sorbose is formed. In the presence of DPN fructose is produced. Both products of the oxidation of sorbitol have been identified by paper chromatography, optical rotation, crystaline form and melting point of the phenylosazones. The fructose can then be phosphorylated and further oxidized by cell-free extracts by means of the Horecker pentose cycle. Both hexose and pentose were shown to accumulate in digestion mixtures, when TPP was removed from transketolase. The oxidation of a number of synthetic polyhydroxy compounds has been shown to be catalyzed by non-specific dehydrogenase systems of A. suboxydans. DPN-specific sorbitol dehydrogenase has been purified a minimum of 13 fold by a three step procedure. This enzyme has been shown to be sorbitol specific. Some of the mdoerhey dcroomgmeonna sseu gaacrt iavlictoyh owlesr ea nndo ta acfteiwv ec otmopwoaurndd st hseh ofwiinnagl high enzyme preparation. Mannitol dehydrogenase is TPN specific and may be the same enzyme as the TPN-sorbitol dehydrogenase. Both theseenzymes proportionately lose activity in the purification of the DPN sorbitol dehydrogenase. Mannitol is three times as active as sorbitol toward the preparations studied. All attempts to separate the TPN-activity from the DPN-activity failed. Both these enzymes have a pH optimum of 8.5 and are stimulated by Mg+ + and Mn+ +. However, the TPN enzyme is more fragile, and the DPN enzyme has a much broader range of activity with pH. A heat denaturation method involving protection of the enzyme by both the cofactor and substrate was used for the DPN linked sorbitol dehydrogenase. This effect has not previously been shown.
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