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Title: Enzymic synthesis of phenolic glycosides
Author: Hopkinson, Shirley Maureen
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1965
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An enzyme from the mould Aspergillus niger with maltose: dihydroxybenzene glucosyl transferase activity has been studied in vitro. The products from a crude enzyme digest with maltose as the glucosyl-donor and resorcinol as the acceptor were isolated and identified. These were m-hydroxyphenyl a-D-glucoside (MHPG) and the corresponding a-isomaltoside, (l),and a-maltoside, (Il).Analogous o-hydroxyphenyl compounds were isolated from digests using catechol as the acceptor. An assay procedure for the enzyme is described, using a vanillin reagent to determine the concentration of the MHPG formed. Preliminary fractionation procedures, examined in an attempt to purify the enzyme, included heat denaturation,(NH4)2SO4, acetone and pH precipitation. The latter proved to be the most efficient. As a second step, gel filtration on Sephadex proved less effective than ion exchange chromatography on DEAE-cellulose, using Cl gradient elution. This method resolved the maltose: dihydroxybenzeneglucosyltransferase activity into two components, X and Y.The pH values for optimum activity of X and Y were 4.5 and 5.1, respectively. At pH 5.1, the respective temperature optima were 380 and 24[degrees]C. X was thermolabile at 50[degrees]C, whereas Y was stableat this temperature. In time-course studies on enzymic formation of MHPG, X exhibited Michaelis-type kinetics, whereas Y did not. Donor and acceptor specificities for X and Y proved to be very similar, that for the acceptor being relatively low. Preliminary kinetic evidence suggested that X, and possibly Y also, has an acceptor site as well as a donor site. Inhibitor studies provided some evidence as to the possible nature of these active sites. 0-a-D-glucosyl-a-D-glucose derivatives (I) and (II) were formed enzymically by stepwise glucosylation of resorcinol with X. Y appeared to form (I), but not (II).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biochemistry