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A. N. Hall

Bio: A. N. Hall is an academic researcher. The author has contributed to research in topics: Glycoside & Alkaline hydrolysis (body disposal). The author has an hindex of 2, co-authored 2 publications receiving 29 citations.


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Book ChapterDOI
TL;DR: The chapter focuses on the mechanism of catalysis and uncompetitive inhibition and provides analyses of studies reporting distinctive immunochemical properties as well as physical properties of enzymes prepared from several organs as guidelines for working in this field.
Abstract: Publisher Summary Isoenzyme refers to a biochemically distinct class of catalytically active proteins with the same specificity of bond cleavage or alteration, which can occupy several zones following electrophoresis. The chapter focuses on the mechanism of catalysis and uncompetitive inhibition and provides analyses of studies reporting distinctive immunochemical properties as well as physical properties of enzymes prepared from several organs. In the case of alkaline phosphatase, the studies rely on a combination of organ source, biochemical properties, and electrophoretic distinctions as guidelines for working in this field. Placental alkaline phosphatase is an isoenzyme of alkaline phosphatase, which can be distinguished from other alkaline phosphatases by biochemical means. The different molecular forms of this isoenzyme, which can be produced and separated by physical means, are referred as variants of placental alkaline phosphatase. Hyperphosphatasemia in diseases of liver and bone has made the serum alkaline phosphatase determination the most frequently demanded enzyme assay.

187 citations

Journal ArticleDOI
TL;DR: The data presented here led to the suggestion of the main lines of a reaction mechanism for the two glucosidases: prptonation of the glycosidic oxygen is followed by the liberation of the "aglycone" with formation of an oxocarbonium ion, which is temporarily stabilized by a carboxylate group.

78 citations

Journal ArticleDOI
TL;DR: In this article, the authors evaluate the fundamental connections between the anomeric effect and a broad variety of O-functional groups and highlight the vast implications of AE for the structure and reactivity of organic O-functionalities.
Abstract: Although carbon is the central element of organic chemistry, oxygen is the central element of stereoelectronic control in organic chemistry. Generally, a molecule with a C–O bond has both a strong donor (a lone pair) and a strong acceptor (e.g., a σ*C–O orbital), a combination that provides opportunities to influence chemical transformations at both ends of the electron demand spectrum. Oxygen is a stereoelectronic chameleon that adapts to the varying situations in radical, cationic, anionic, and metal-mediated transformations. Arguably, the most historically important stereoelectronic effect is the anomeric effect (AE), i.e., the axial preference of acceptor groups at the anomeric position of sugars. Although AE is generally attributed to hyperconjugative interactions of σ-acceptors with a lone pair at oxygen (negative hyperconjugation), recent literature reports suggested alternative explanations. In this context, it is timely to evaluate the fundamental connections between the AE and a broad variety of O-functional groups. Such connections illustrate the general role of hyperconjugation with oxygen lone pairs in reactivity. Lessons from the AE can be used as the conceptual framework for organizing disjointed observations into a logical body of knowledge. In contrast, neglect of hyperconjugation can be deeply misleading as it removes the stereoelectronic cornerstone on which, as we show in this review, the chemistry of organic oxygen functionalities is largely based. As negative hyperconjugation releases the “underutilized” stereoelectronic power of unshared electrons (the lone pairs) for the stabilization of a developing positive charge, the role of orbital interactions increases when the electronic demand is high and molecules distort from their equilibrium geometries. From this perspective, hyperconjugative anomeric interactions play a unique role in guiding reaction design. In this manuscript, we discuss the reactivity of organic O-functionalities, outline variations in the possible hyperconjugative patterns, and showcase the vast implications of AE for the structure and reactivity. On our journey through a variety of O-containing organic functional groups, from textbook to exotic, we will illustrate how this knowledge can predict chemical reactivity and unlock new useful synthetic transformations.

60 citations

Book ChapterDOI
Giorgio Semenza1
01 Jan 1976
TL;DR: This chapter will first review the general knowledge about small intestinal oligo- and disaccharidases and then will cover in more detail what is known about the structure and catalytic mechanism of two of them, i.e., the sucrase-isomaltase complex.
Abstract: This chapter will first review our general knowledge about small intestinal oligo- and disaccharidases and then will cover in more detail what is known about the structure and catalytic mechanism of two of them, i.e., the sucrase-isomaltase complex. Finally, the role of sucrase-isomaltase as group translocator across natural and artificial membranes will be discussed.

49 citations

Journal ArticleDOI
TL;DR: Plots of log V m for each substrate versus the Hammett σ constants for the substituent suggest that a nucleophilic attack occurs and that a free carbonium ion form of the substrate is not involved at the rate-determining step in the mechanism.

45 citations