Schardinger enzyme

This enzyme, sometimes also called the Schardinger enzyme, occurs in milk. It is capable of " oxidising" acetaldehyde to acetic acid, and also the purine bases xanthine and hypoxanthine to uric acid. The former reaction is not a simple direct oxidation and is assumed to take place as follows. The enzyme activates the hydrated form of the aldehyde so that it readily parts w ith two hydrogen atoms in the presence of a suitable hydrogen acceptor such as methylene-blue the latter being reduced to the colourless leuco-compound. The oxidation of certain substrates will not take place in the absence of such a hydrogen acceptor. 

Dixon M. 1927. The effect of cyanide on the Schardinger enzyme. Biochem J 21 840. 

Kutase.—Dixon and Lutwak-Mann (1937) have shown that two distinct enzymes are capable of catalysing the oxidation of aldehydes (i.) Aldehyde oxidase (Schardinger enzyme), which... 

Note. The cyclic oligosaccharides arising from enzymic transglycosylation of starch have been referred to as Schardinger dextrins. These names (and those of the cyclohexaamylose type) are not recommended, but the abbreviation CD is tolerated. 

Prior to 1939, however, it was not known whether the cyclodextrins were products of the synthetic metabolism of Bacillus macerans, and therefore, perhaps, quite different from the components of starch, or whether they were formed by a single enzyme and therefore closely related to the starch structure. Then, Tilden and Hudson announced the discovery of a cell-free enzyme preparation from cultures of Bacillus macerans which had the ability to convert starch into the Schardinger dextrins without the production of maltose, glucose, or any other reducing sugars. They thus concluded that the Schardinger dextrins were either the true components of starch or closely related to such true components. 

Dr. French was a prolific contributor of research articles to professional chemical and biochemical journals. He published many reviews and methods articles in Annual Reviews of Biochemistry, Methods in Enzymology, Advances in Carbohydrate Chemistry and Biochemistry, Starch Chemistry and Technology, and The Enzymes. Two articles that were published in this Advances are The Raffinose Family of Oligosaccharides in Vol, 9 and The Schardinger Dextrins in Vol. 12. He was a member of the Editorial Advisory Boards of the Journal of Biological Chemistry and Carbohydrate Research, and of the Board of Advisors for Advances in Carbohydrate Chemistry and Biochemistry. 

The enzyme will also transfer glucose to other carbohydrate acceptors such as Schardinger dextrin, or mal-totetraose to form an a-(l- 6)-linked glucosyl Schardinger dextrin or a branched pentasaccharide, or even to free glucose to form isomaltose (15,33). In this respect the glucosidase (dextrin 6-... 

A schematic depiction of the mechanism at the active site of beta-amylase has been described in terms of an induced-fit concept. This scheme accounts qualitatively for the specificity of the enzyme (the exclusive formation of maltose) the failure to bypass branchpoints and the inhibition by maltose, interior parts of starch chains, and Schardinger dextrins. 

While the enzymic approach must be refined and rationalized, present evidence is completely in accord with the concept of linear and branched structures for the two starch components. The theory has been advanced that the individual alpha and beta Schardinger dextrins originate from specific starch fractions, but this appears to be untenable. No satisfactory mechanism has been proposed to account for the production of the several crystalline dextrins. 

Transglycosylase mechanism in enzymic synthesis of Schardinger dextrins... 

The ability of culture filtrates to produce Schardinger dextrins (identified as their crystalline iodine complexes) has been used " as a means for the identification of B. macerans. So far no other source, microbial or otherwise, has been foimd for this unique enzyme. 

The Schardinger dextrins have also been reported " to lie stable to alpha-type amylases. However, in a study of the action of salivary amylase, French and coworkers " found that while the a-dextrin is essentially completely resistant, the /3-dextrin is attacked very slowly indeed and the 7-dextrin is attacked about 1 % as rapidly as is starch. Here it is clear that the ring size exerts an effect possibly the smaller rings have greater rigidity and hence cannot adapt their shape to that inquired by the enzyme. 

Early reports of the partial hydrolj-sis of the Schardinger dextrins by paii-creatio amylase indicated that a-tetraamylose is more susceptible than /3-hexa-aniylose. This is most likely a reflection of the relative degree of purity of the/3-dex-trins the crude a-dextrin preparations probably contained starchy impurities which were attacked by the enzyme used. 

A common observation, which constitutes a practical nuisance in the laboratory, is the growth of molds on unprotected " Schardinger dextrin solutions hence certain molds at least must have the enzymic machinery for converting Schardinger dextrins into more conventional energy sources. 

It is the writer s expectation that the Schardinger dextrins, and the enzyme from B. macerans which produces them, will continue to serve, delight, teach, and intrigue the carbohydrate chemist for many years to come. 

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