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MetaCyc Compound Class: α-amylose

Synonyms: an α-amylose

Superclasses: all carbohydratesa carbohydratea glycana polysaccharidea glucana linear alpha-D-glucana 1,4-alpha-D-glucan
all carbohydratesa carbohydratea glycana polysaccharidea glucanstarch

Starch is a mixture of the two polymeric carbohydrates (polysaccharides) α-amylose and amylopectin.

α-Amylose contains up to several thousand glucosyl units linked almost exclusively in linear α(1->4) linkages, with very few branches of α(1->6) linkages. In amylopectin, on the other hand, branching is common, and occurs approximately every 24-30 glucose units.

α-Amylose accounts for 30% of starch, while amylopectin accounts for the other 70%.

Glycan icon:

α-amylose compound structure

Reactions known to consume the compound:

starch biosynthesis :
ADP-α-D-glucose[chloroplast stroma] + n (1,4-α-D-glucosyl)(n)[chloroplast stroma] → ADP[chloroplast stroma] + n α-amylose[chloroplast stroma]
n α-amylose → n amylopectin + n H2O
n amylopectin + α-amylose → n starch

glycogen biosynthesis I (from ADP-D-Glucose) :
a 1,4-α-D-glucan → a glycogen

glycogen degradation III (via anhydrofructose) :
a 1,4-α-D-glucan → n 1,5-anhydro-D-fructose + D-glucopyranose

starch biosynthesis :
n a 1,4-α-D-glucan → a (1,6)-α-D-glucosyl-(1,4)-α-glucan highly branched + n H2O

Not in pathways:
(1,4-α-D-glucosyl)(n) + H2O → (1,4-α-D-glucosyl)(n-1) + D-glucopyranose
a 1,4-α-D-glucan + H2O → a 1,4-α-D-glucan + β-maltose
sucrose + (1,4-α-D-glucosyl)(n) → D-fructofuranose + (1,4-α-D-glucosyl)(n+1)
a 1,4-α-D-glucan + n H2O → n a 1,4-α-D-glucan
a 1,4-α-D-glucan + n H2O → a 1,4-α-D-glucan + n maltotetraose
a 1,4-α-D-glucan + H2O → a 1,4-α-D-glucan + maltotriose
a 1,4-α-D-glucan + H2O → a 1,4-α-D-glucan + maltohexaose
a 1,4-α-D-glucan[periplasm] + n H2O[periplasm]a 1,4-α-D-glucan[periplasm] + maltohexaose[periplasm]

starch degradation I :
starch → a linear malto-oligosaccharide

starch degradation II :
starch[chloroplast stroma] + n ATP[chloroplast stroma] + n H2O[chloroplast stroma] → a 6-phosphogluco-amylopectin[chloroplast stroma] + n AMP[chloroplast stroma] + n phosphate[chloroplast stroma]

starch degradation III , starch degradation IV :
starch[extracellular space] → a cyclodextrin[extracellular space]

starch degradation V :
starch[extracellular space] + H2O[extracellular space] → a maltodextrin(n)[extracellular space] + maltose[extracellular space] + D-glucopyranose[extracellular space]

Not in pathways:
starch + n H2O → n α-maltose
starch + n H2O → a long-linear glucan
starch + n H2O → a large-branched glucan
starch + H2O → maltose + glucose

starch degradation II :
a glucan[chloroplast stroma] + maltotriose[chloroplast stroma]a glucan[chloroplast stroma] + D-glucopyranose[chloroplast stroma]

Reactions known to produce the compound:

cellulose and hemicellulose degradation (cellulolosome) :
a feruloyl-polysaccharide + H2O → ferulate + a polysaccharide + H+

Reactions known to both consume and produce the compound:

glycogen biosynthesis I (from ADP-D-Glucose) , starch biosynthesis :
ADP-α-D-glucose + (1,4-α-D-glucosyl)(n) ↔ ADP + (1,4-α-D-glucosyl)(n+1)

Not in pathways:
(1,4-α-D-glucosyl)(n) + phosphate ↔ (1,4-α-D-glucosyl)(n-1) + α-D-glucopyranose 1-phosphate

In Reactions of unknown directionality:

Not in pathways:
a 1,4-α-D-glucan = a cyclodextrin
n a 1,4-α-D-glucan = n starch + n H2O
(1,4-α-D-glucosyl)(n) = (1,4-α-D-glucosyl)(n-1) + a (1,6)-α-D-glucosyl-(1,4)-α-glucan
a 1,4-α-D-glucan + a 1,4-α-D-glucan = a 1,4-α-D-glucan + a 1,4-α-D-glucan
α-maltose 1-phosphate + (1,4-α-D-glucosyl)(n-1) = (1,4-α-D-glucosyl)(n+1) + phosphate
a nucleoside diphosphate-glucose + a 1,4-α-D-glucan = a nucleoside diphosphate + a 1,4-α-D-glucan
(1,4-α-D-glucosyl)(n) + (1,6-α-D-glucosyl)(m) = (1,4-α-D-glucosyl)(n-1) + (1,6-α-D-glucosyl)(m+1)

Not in pathways:
n a 1,4-α-D-glucan = n starch + n H2O

Not in pathways:
a linear α-D-glucan + sucrose = an alternan
a linear α-D-glucan + ATP + H2O = [phospho-α-glucan] + AMP + phosphate + 2 H+

This compound has been characterized as an alternative substrate of the following enzymes: α-amylase

Revised 15-Mar-2013 by Caspi R, SRI International


Ball03: Ball SG, Morell MK (2003). "From bacterial glycogen to starch: understanding the biogenesis of the plant starch granule." Annu Rev Plant Biol 54;207-33. PMID: 14502990

Ball11: Ball S, Colleoni C, Cenci U, Raj JN, Tirtiaux C (2011). "The evolution of glycogen and starch metabolism in eukaryotes gives molecular clues to understand the establishment of plastid endosymbiosis." J Exp Bot 62(6);1775-801. PMID: 21220783

Buleon98: Buleon A, Colonna P, Planchot V, Ball S (1998). "Starch granules: structure and biosynthesis." Int J Biol Macromol 23(2);85-112. PMID: 9730163

Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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