Mechanism of maltal hydration catalyzed by. beta. -amylase: Role of protein structure in controlling the steric outcome of reactions catalyzed by a glycosylase

Journal Article · Tue Jul 09 00:00:00 EDT 1991 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00241a020· OSTI ID:5046060

Kitahata, Sumio ^[1]; Chiba, S ^[2]; Brewer, C F; Hehre, E J ^[3]

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1. Osaka Municipal Technical Research Inst. (Japan)
2. Hokkaido Univ. (Japan)
3. Albert Einstein Coll. of Medicine, Bronx, NY (United States)

Crystalline (monomeric) soybean and (tetrameric) sweet potato {beta}-amylase were shown to catalyze the cis hydration of maltal ({alpha}-D-glucopyranosyl-2-deoxy-D-arabino-hex-1-enitol) to form {beta}-2-deoxymaltose. As reported earlier with the sweet potato enzyme, maltal hydration in D{sub 2}O by soybean {beta}-amylase was found to exhibit an unusually large solvent deuterium kinetic isotope effect (V{sub H}/V{sub D}=6.5), a reaction rate linearly dependent on the mole fraction of deuterium, and 2-deoxy-(2(a)-{sup 2}H)maltose as product. These results indicate (for each {beta}-amylase) that protonation is the rate-limiting step in a reaction involving a nearly symmetric one-proton transition state and that maltal is specifically protonated from above the double bond. That maltal undergoes cis hydration provides evidence in support of a general-acid-catalyzed, carbonium ion mediated reaction. Of fundamental significance is that {beta}-amylase protonates maltal from a direction opposite that assumed for protonating strach, yet creates products of the same anomeric configuration from both. Such stereochemical dichotomy argues for the overriding role of protein structures is dictating the steric outcome of reactions catalyzed by a glycosylase, by limiting the approach and orientation of water or other acceptors to the reaction center.

• OSTI ID: 5046060
• Journal Information: Biochemistry; (United States), Vol. 30:27; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
HEAVY WATER
ISOTOPE EFFECTS
MALTOSE
HYDRATION
AMYLASE
GAS CHROMATOGRAPHY
NMR SPECTRA
SOYBEANS
STEREOCHEMISTRY
CARBOHYDRATES
CHROMATOGRAPHY
DISACCHARIDES
ENZYMES
FOOD
GLYCOSYL HYDROLASES
HYDROGEN COMPOUNDS
HYDROLASES
O-GLYCOSYL HYDROLASES
OLIGOSACCHARIDES
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PLANTS
SACCHARIDES
SEPARATION PROCESSES
SOLVATION
SPECTRA
VEGETABLES
WATER
550201* - Biochemistry- Tracer Techniques