Biological method for protection of 6-position of sucrose and its use in synthesis of disaccharide high-intensity sweetener.

A general method for protecting the 6 primary hydroxyl position of sucrose is described. It involves the production of glucose-6-acetate by fermentation of glucose using a strain of Bacillus megaterium followed by conversion to sucrose-6-acetate as a kinetic product using a specially selected fructosyl transferase producted by a newly isolated strain of Bacillus subtilis. The sucrose-6-acetate was found to be more lipophilic than expected, and this property aided its purification by chromatography. Pure sucrose-6-acetate may then be chlorinated and subsequently deacetylated to give the high-intensity sweetener 4,1',6'-trichlo-4,1',6'-trideoxygalactosucrose (sucralose) in high yields. This process involves fewer steps than are required for chemical synthesis using trityl chloride and acetic anhydride. Related intensely sweet molecules which were synthesized by similar methods included 4,1',6'-trichloro, 4,1',6'-trideoxy L-arabinosucrose, and 4,1',6'-trichloro-4,6,1',6'-tetradeoxy-galactosucrose. They were obtained from xylose and 6-deoxyglucose, respectively, via the intermediates xylsucrose and 6-deoxysucrose, formed by the reaction of the fructosyl transferase on the monosaccharide acceptors.

Biocatalytic synthesis of disaccharide high-intensity sweeterner sucralose via a tetrachlororaffinose intermediate.

A second high-yielding bioorganic synthesis of the highintensity sweetener sucralose (4,1',6'-trichloro-4,1',6'-trideoxygalactosucrose) is described. This procedure involves the chemical chlorination of raffinose to form a novel tetrachloroaffinose intermediate (6,4',1'',6''-tetrachloro-6,4',1'',6''-tetradeoxygalactoraffinose; TCR) followed by the enzymic hydrolysis of the alpha-1-6 glycosidic bond of TCR to give sucralose and 6-chlorogalactose. Commercial enzyme preparations and microorganisms were screened to select alpha-galactosidases which have high catalytic activity on this compound. The most active enzyme was produced by a strain of Mortierella vinacea and had a maximum rate of 118 mumol sucralose/g dry weight cells/h, which was approximately 5% of the activity toward raffinose, and a K(m) of 5.8 mM toward TCR. The enzyme could be used in the form of mycelial pellets in a continuous packed bed column reactor. The reaction was also studied in a water-immiscible hydrophilic organic solvent, such as methyl isobutyl ketone, to overcome the poor aqueous solubility of TCR and to increase volumetric productivity. Synthesis of raffinose was achieved from saturated aqueous solutions of galactose and sucrose using a selected alpha-galactosidase from Aspergillus niger. When raffinose is used as a starting material for sucralose synthesis, this route has fewer steps than either the preceeding method using glucose-6-acetate as an intermediate or the complete chemical synthesis from sucrose. The relative merits of the two bioorganic routes and the utility of such methods to synthesize new sugars are discussed.

The use of a hydrophobic resin as a product reservoir in steroid transformations.

Particles of the hydrophobic resin polydimethylsiloxane were found to preferentially accumulate steriods on the basis of their hydrophobicity. Thus, the resin selectively sorped the steroid products resulting from the transformation of diosgenin by Nocardia rhodochrous, with the result that higher yields of the later biotransformation product, 1-dehydrodiosgenone, and lower yields of the first product, diosgenone, were obtained than in the absence of resin. Furthermore, steroids accumulated by the resin were available for further biotransformation, so that a two-step reaction forming androstenes from a crude extract of furostanol glycosides (obtained from fenugreek seed) could be carried out. The first step involves deglycosylation and is catalyzed by Fusarium solani. In the presence of resin the water-insoluble diosgenin product becomes sorped to the resin and can be easily transferred to a second fermentation in which diosgenone, 1-dehydrodiosgenone, and androstenes were formed by Mycobacterium phlei. These compounds were completely accumulated by the resin at the end of the fermentation. This procedure is logistically more convenient than the conventional chemical process and illustrates the potential of biotechnological processes in which simultaneous reaction, product isolation, and product purification occur.

The extraction and mechanism of a novel isomaltulose-synthesizing enzyme from Erwinia rhapontici.

The single enzyme that mediates the bioconversion is demonstrated to be located in the cells' periplasmic space, a site that facilitates its use as an industrial biocatalyst, and to be a previously undescribed hexosyltransferase with four novel features. The enzyme is sucrose-specific, and has an intramolecular mechanism in which both glucose and fructose residues appear to be enzyme-bound. Thirdly, it is reaction-non-selective, forming simultaneously isomaltulose and a second hitherto uncharacterized alpha-(1----1)-linked disaccharide (trehalulose), by hydrolysis of sucrose followed by reaction of glucose with the C-6 and C-1 positions of the fructofuranose respectively. Finally, on extended incubation an unusual recycling mechanism caused the concentration of isomaltulose, the kinetically preferred product, to reach a transient maximum concentration and then fall, and the concentration of trehalulose, the thermodynamically favoured product, to rise slowly.

The characterization and interconversion of three forms of cholesterol oxidase extracted from Nocardia rhodochrous.

The physical properties and the methods used for interconversion of three forms of cholesterol oxidase extracted from Nocardia rhodochrous by treatment with Triton X-100, trypsin or buffer alone provide evidence that these forms differ chiefly in the possession or absence of a hydrophobic anchor region connected by a trypsin-sensitive region. The hydrophobic domain normally integrates the enzyme into the cell membrane and confers amphipathic properties on the solubilized enzyme, causing adsorption to hydrophobic resins, aggregation when detergent is removed and formation of mixed micelles with detergent and cholesterol resulting in surface-dilution kinetic behaviour and activation by relatively high concentrations of water-miscible solvents. By contrast, only the enzymic fragment is extracted with trypsin and it behaves as a conventional soluble enzyme and does not aggregate or interact with hydrophobic resins, detergents or water-miscible solvents. As no phospholipid could be detected in the enzyme extracts, the detergent appears to act as a substitute for the cell-membrane lipids that would normally interact with the hydrophobic region. This cholesterol oxidase is an example of a prokaryotic enzyme possessing two closely associated catalytic functions, dehydrogenase and isomerase activities, and an anchoring function.

A benign deficiency of typeB beta-galactosidase in human liver.

The type A or 'acid' and type B or 'neutral' beta-galactosidase activities have been measured in post-mortem liver samples from individuals dying of non-genetic diseases and patients dying of ganglioside storage disease other than GM1 gangliosidosis. The type A activities fell within the established normal range in all samples. The type B activities showed a biomodal distribution suggesting the occurrence of two distinct populations of human individuals. The greater proportion had activities within the range 11.67 pkat/mg of protein (+/- 3.33, S.D.), while others had lower activities in the range 0.48 pkat/mg of protein (+/- 0.38, S.D.). No clinical symptoms were associated with the much lower type B beta-galactosidase activities and it appears that this beta-galactosidase deficiency could be found in the original tissues. Methods of screening for type B beta-galactosidase deficiency are described and the significance of this enzyme deficiency is discussed.

The separation and characterization of the methylumbelliferyl beta-galactosidases of human liver.

1. A previously uncharacterized form of human liver acid beta-galactosidase (EC 3.2.1.23), possibly a dimer of molecular weight 160 000, was resolved by gel filtration. It has the same ability to hydrolyse GM1 ganglioside as the two other acid beta-galactosidase forms. 2. The low-molecular-weight forms of acid beta-galactosidase undergo salt-dependent aggregation. 3. The high-molecular-weight component may consist of the low-molecular-weight forms bound to membrane fragments. It can be converted completely into a mixture of these forms. 4. The neutral beta-galactosidase activity can be resolved into two forms by DEAE-cellulose chromatography. They differ in their response to Cl-ions. 5. A new nomenclature is suggested for the six beta-galactosidases so far found in human liver. 6. The enzymic constituents of the beta-galactosidase bands resolved by electrophoresis were re-examined. The A band contains three components. A two-dimensional electrophoretic procedure for resolving the A band is described. 7. The effect of neuraminidase treatment on the behaviour of beta-galactosidases in various separation systems is examined.