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Acetohydroxyacid synthase (AHAS) and acetolactate synthase (ALS) are thiamine diphosphate (ThDP)-dependent enzymes that catalyze the decarboxylation of pyruvate to give a cofactor-bound hydroxyethyl group, which is transferred to a second molecule of pyruvate to give 2-acetolactate. AHAS is found in plants, fungi, and bacteria, is involved in the(More)
Purpose. To develop a facile functional assay for quantitative determination of the apparent affinities of compounds that interact with the taxol binding site of P-glcoprotein (P-gp) in Caco-2 cell monolayers. Methods. A transport inhibition approach was taken to determine the inhibitory effects of compounds on the active transport of [3H]-taxol, a known(More)
This paper examines the effect of water content, water activity, and glass transition temperature (T(g)) on the deamidation of an asparagine-containing hexapeptide (VYPNGA; Asn-hexapeptide) in lyophilized poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) at 50 degrees C. The rate of Asn-hexapeptide deamidation increases with increasing water(More)
The deamidation reactions of asparagine residues in alpha-helical and beta-turn secondary structural environments of peptides and proteins are reviewed. Both kinds of secondary structure tend to stabilize asparagine residues against deamidation, although the effects are not large. The effect of beta-sheet structures on asparagine stability is unclear,(More)
The deamidation kinetics of four model peptides (AcGQNGG, AcGQNDG, AcGQNEG, and AcGQNQG) were studied in solution (70 degrees C, pH 5-10) and in lyophilized solids [70 degrees C, 50% relative humidity, "effective pH" ('pH') 5-10] containing polyvinyl pyrrolidone. AcGQNGG, AcGQNEG, and AcGQNQG degraded exclusively through Asn deamidation, whereas AcGQNDG(More)
The Asn residue in the pentapeptide Asn-Gln-Asn-Glu-Gly undergoes racemization at the Calpha center in the course of deamidation of this residue through a succinimide intermediate. The succinimide intermediate is known to racemize at the corresponding center, leading to racemized products of deamidation. Return of this intermediate to reactant Asn is very(More)
Domain motions of S-adenosyl-l-homocysteine (AdoHcy) hydrolase have been detected by time-resolved fluorescence anisotropy measurements. Time constants for reorientational motions in the native enzyme were compared with those for enzymes where key residues were altered by site-directed mutation. Mutations M351P, H353A, and P354A were selected in a hinge(More)