Starch lyase

Because the reaction is degradative, it requires a starch chain, and the product of a single event is a-Glc 1-P and a starch chain that has had one or more glucosyl residues removed. It is, therefore, not surprising that the reaction in the reverse synthetic direction also requires a starch chain or so-called primer. The primer hypothesis for the synthesis of polysaccharide was, thus, developed from an enzyme that was actually a degradative enzyme and not a synthetic enzyme. Nevertheless, the primer-dependent mechanism has been incorrectly assumed for the biosynthesis of starch for over 60 years. 

Enzymes are used in the determination of polysaccharide structures. Because enzymes have specificity, i.e. they produce specific products of low molecular weight and can cleave specific kinds of bonds they can be used to determine the fine structure of starch. A first premise, however, is that the action patterns and specificity must need to be thoroughly investigated and elucidated before reliable information can be obtained about the structure of the polysaccharide or oligosaccharide being studied. 

The major enzymes that have been used for studying structures of starch polymers and fragments from them are the endo-acting a-amylases, the exo-acting glucoamylase and (3-amylases, and the debranching enzymes, isoamylases and pullulanases. These enzymes have varied and diverse specificities that have been extensively studied (see previous sections). 

Although partial acid-catalyzed hydrolysis had ascertained that the major linkage in starch was a-(l— 4), with lesser amounts of a-(l— -6) branch linkages, controversies developed over the possible presence of other types of linkages.243-245 a- (1 3), 

The doubly branched dextrins, 64,66-di-a-D-glucopyranosylmaltohexaose and 63,65-di -a-D-glucopyranosylmaltopentaose, isolated by Kainuma and French17 after action of porcine pancreatic a-amylase on waxy maize starch, established that the a-(l— -6) branch linkages could be as close as having one glucosyl unit between them. No saccharides were found that indicated that the branch linkages could be adjacent to each other. 

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Figure 7.20 Mechanism for the formation of 1,5-anhydro-D-fructose from starch by the exo-acting starch lyase.

The mechanism of cleavage of the a-(l—A) linkage by starch lyase involves removal of the proton on C-2, with subsequent formation of a double bond between C-2 and C-l, and simultaneous displacement of the protonated glycosidic oxygen atom. This results in the release of the starch chain with one less glucosyl unit and the formation of the enol of 1,5-anhydro-D-fructose (Figure 7.20). 

A new exo-acting enzyme, a starch lyase, has been discovered in red seaweeds and fungi. It removes glucose residues at the non-reducing-ends of starch chains and converts them into 1,5-anhydro-D-fructopyranose units. This product has been found to be an antioxidant and a new and versatile chiral building block for the formation of fine chemicals [98,99]. 

Lyases Acting on Neutral Polysaccharides Only one group of enzymes of this type is known, these are the amylolyases or (1 4)-o -glucan (starch) lyases [EC 4.2.2.13] that specifically... 

Lyases, which cleave various bonds by means other than hydrolysis and oxidation, such as starch to glucose. 

A-Acetyl neuraminic acid aldolase [from Clostridium perfringens, A-acetylneuraminic acid pyruvate lyase] [9027-60-5] [EC 4.1.3.3]. Purified by extraction with H20, protamine pptn, (NH4)2S04 pptn, Me2CO pptn, acid treatment at pH 5.7 and pptn at pH 4.5. The equilibrium constant for pyruvate + n-acetyl-D-mannosamine ++ /V-acetylneuraminidate at 37° is 0.64. The Km for A-acetylneuraminic acid is 3.9mM in phosphate at pH 7.2 and 37°. [Comb and Roseman Methods in Enzymology 5 391 1962). The enzyme from Hogg kidney (cortex) has been purified 1700 fold by extraction with H20, protamine sulphate pptn, (NH4)2S04 pptn, heat treatment between 60-80°, a second (NH4)2S04 pptn and starch gel electrophoresis. The Km for A-acetylneuraminic acid is 1.5mM. [Brunetti et al. JBC 237 2447 1962). 

Pineapple oil, peel-oil content and aldehyde composition, see also Citrus oils Pin milling, starch isolation, 673, 677 Pipetting technique, 754-755 PL. see Pectic lyase... 

S. Yu, T. Ahmad, L. Kenne, and M. Pedersen, a-1,4-Glucan lyase, a new class of starch glycogen degrading enzyme. 3. Substrate specificity, mode of action, and cleavage mechanism, BBA General Subjects, 1244 (1995) 1-9. 

S. Yu, K. Bojsen, B. Svensson, and J. Marcussen, a-l,4-Glucan lyases producing 1,5-anhydro-D-fructose from starch and glycogen have sequence similarity to a-glucosidases, BBA Protein Struct. Mol. Enzym., 1433 (1999) 1-15, review, 53 references. 

SCHEME 1. Action of a-(l 4)-glucan lyase on floridean starch (the monosaccharide derivatives, which are split from the nonreducing ends of the polysaccharide chains probably in the form of 2-hydroxyglucal, are tautomerized to the more stable 1,5-anhydro-D-fructose, 5). 

Red algae enzymes in the starch degradation pathway (e.g., a-1,4-glucan lyase and others)... 

Prod, by the action of a-l,4-glucan lyase on a-glucans such as starch. Exists in rat liver, fungi and algae. Precursor of 2-Hydroxy-2-(hydroxymethyl)-2//-pyran-3(6/T)-one in Morchella vulgaris (morel) and of Echinosporin in Peziza echinospora, Antioxidant. 

Dissolution of starch grains in endosperm observed Isocitrate lyase (see Sect. 6.4.5) present in scutellum Axis accumulates starch... 

In addition to the above findings there is nevertheless a body of evidence which raises doubts concerning the relationship between axis and cotyledons in food mobilization. We should recall, in this context, that a- and j8-amylase have been reported to reach higher levels in detached pea cotyledons [118], that starch and protein breakdown occur in detached pea cotyledons [10] and that a-amylase development in P. vulgaris cotyledons is unaffected by excision, at least over the first four days. Similarly, removing the axis has no deleterious effect on isocitrate lyase activity in cotyledons of Arachis hypogaea (peanut) and the enzyme reaches a level identical to that in intact seeds [80]. 

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